Article

Normal-eye Zernike coefficients and root-mean-square wavefront errors

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Abstract

To compare aberrometry measurements from multiple sites and compute mean Zernike coefficients and root-mean-square (RMS) values for the entire data pool to serve as a reference set for normal, healthy adult eyes. Northeastern State University, Tahlequah, Oklahoma, USA. Data were collected from 10 laboratories that measured higher-order aberrations (HOAs) in normal, healthy adult eyes using Shack-Hartmann aberrometry (2560 eyes of 1433 subjects). Signed Zernike coefficients were scaled to pupil diameters of 6.0 mm, 5.0 mm, 4.0 mm, and 3.0 mm and corrected to a common wavelength of 550 nm. The mean signed and absolute Zernike coefficients across data sets were compared. Then, the following were computed: overall mean values for signed and absolute Zernike coefficients; polar Zernike magnitudes and RMS values for coma-like aberrations (Z(3)(+/-1) and Z(5)(+/-1) combined); spherical-like aberrations (Z(4)(0) and Z(6)(0) combined); and 3rd-, 4th-, 5th-, and 6th-order, and higher-order aberrations (orders 3 to 6). The different data sets showed good agreement for Zernike coefficients values across most higher-order modes, with greater variability for Z(4)(0) and Z(3)(-1). The most prominent modes and their mean absolute values (6.0-mm pupil) were, respectively, Z(3)(-1) and 0.14 microm, Z(4)(0) and 0.13 microm, and Z(3)(-3) and 0.11 microm. The mean total higher-order RMS was 0.33 microm. There was a general consensus for the magnitude of HOAs expected in normal adult human eyes. At least 90% of the sample had aberrations less than double the mean values reported here. These values can serve as a set of reference norms.

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... associated variable conditions such as refractive error, age, pupil size and other tissue factors related to the tear film, cornea, lens, aqueous and vitreous. Most existing studies control certain factors such as pupil size by categorizing pupil diameters when analyzing HOA in order to avoid confounding effects [11]. However, pupil size is a continuous measure and the arbitrary grouping of pupil size into discreet categories may cause biased inferences and loss of statistical power due to possible misclassification [12][13][14][15]. ...
... Zernike polynomials in the analyses will be adjusted for pupil sizes. Previous studies adjust for pupil sizes by stratification (dividing patients into different groups according to their pupil sizes) [11,19], such as rescaling pupil sizes into different groups, 6.00 mm, 5.00 mm, etc [8]. Individual pupil sizes are thus not used in the analysis, which potentially result in information loss. ...
... As indicated by the horizontal zero line, most Zernike polynomials are centered at zero, except for Z 310 (horizontal coma), Z 330 (oblique trefoil) and Z 400 (spherical). The mean of oblique trefoil aberrations is negative and the mean of spherical aberrations is positive, which is consistent with the literature [9,11,23,24]. Furthermore, except for Z 400 , the variations in coma and trefoil aberrations are much higher than in the aberrations at higher levels. ...
... The variation in aberration magnitude with temporal frequency follows a power law with an exponent of −17/3 (reFS 44,45 ). In vision science, the aberrations increase with pupil size and typically the higher the Zernike radial order, the lower the magnitude of the aberration 46 . The pupil of the eye is often dilated when imaging the retina to increase resolution. ...
... Diffraction can be minimized by dilating the pupil with mydriatic drops. However, this benefit comes at the cost of additional aberrations exposed by dilation 40,46 . AO increases lateral resolution by a factor of up to five over commercial ophthalmoscopes, permitting resolution of retinal details as small as 2-3 µm after pupil dilation, sufficient to resolve most major cell types in the retina including the densely packed cone photoreceptor cells in the fovea. ...
... There has been extensive reproducibility of ocular aberration measurements and retinal imaging results across different AO ophthalmoscopes and laboratories. Population studies involving thousands of individuals using SH aberrometry have been compared and have demonstrated good agreement 46 . Practically every AO ophthalmoscope built has been used to image cone photoreceptors at different locations in the retina, the density and spacing of which are routinely compared with widely accepted measurements obtained in in vivo imaging [193][194][195] and histological 196 studies. ...
Article
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Adaptive optics (AO) is a technique that corrects for optical aberrations. It was originally proposed to correct for the blurring effect of atmospheric turbulence on images in ground-based telescopes and was instrumental in the work that resulted in the Nobel prize-winning discovery of a supermassive compact object at the centre of our galaxy. When AO is used to correct for the eye’s imperfect optics, retinal changes at the cellular level can be detected, allowing us to study the operation of the visual system and to assess ocular health in the microscopic domain. By correcting for sample-induced blur in microscopy, AO has pushed the boundaries of imaging in thick tissue specimens, such as when observing neuronal processes in the brain. In this primer, we focus on the application of AO for high-resolution imaging in astronomy, vision science and microscopy. We begin with an overview of the general principles of AO and its main components, which include methods to measure the aberrations, devices for aberration correction, and how these components are linked in operation. We present results and applications from each field along with reproducibility considerations and limitations. Finally, we discuss future directions. This Primer provides an overview of the general principles of adaptive optics and explores the different ways in which adaptive optics can correct optical aberrations for high-resolution imaging in the fields of astronomy, vision science and microscopy.
... However, image quality-based predictions in normal eyes range within the here reported limits of agreements towards the subjective refraction [32]. Since the current investigation enrolled only normally sighted participants, the amount of HOAs in the cohort is low and comparable to already reported values [33], as shown in Figure 4. Furthermore, the objective aberrometry measurements that were evaluated for a pupil diameter of 3 mm reduce the impact even further. polychromatic metrics were used to compute refractive correction or by taking into account the Stiles-Crawford effect [28]. ...
... However, image quality-based predictions in normal eyes range within the here reported limits of agreements towards the subjective refraction [32]. Since the current investigation enrolled only normally sighted participants, the amount of HOAs in the cohort is low and comparable to already reported values [33], as shown in Figure 4. Furthermore, the objective aberrometry measurements that were evaluated for a pupil diameter of 3 mm reduce the impact even further. ...
... This small increase in visual acuity can be explained by the fact that the spherical refractive error was around 0.3 D too negative with the objective method. The fact that visual acuity increased only slightly, when the refractive error was adjusted with both of the two subjective methods, is a good indicator for the fact that autorefraction measurement of Figure 4. Comparison of the absolute Zernike coefficient (µm) for the higher order aberrations until fifth order from the current study to normal human subjects for a 3 mm pupil diameter (data from Salmon et al. [33]). ...
Article
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Advancements in clinical measurement of refractive errors should lead to faster and more reliable measurements of such errors. The study investigated different aspects of advancements and the agreement of the spherocylindrical prescriptions obtained with an objective method of measurement (“Aberrometry” (AR)) and two methods of subjective refinements (“Wavefront Refraction” (WR) and “Standard Refraction” (StdR)). One hundred adults aged 20–78 years participated in the course of the study. Bland–Altman analysis of the right eye measurement of the spherocylindrical refractive error (M) identified mean differences (±95% limits of agreement) between the different types of measurements of +0.36 D (±0.76 D) for WR vs. AR (t-test: p < 0.001), +0.35 D (± 0.84 D) for StdR vs. AR (t-test: p < 0.001), and 0.0 D (± 0.65 D) for StdR vs. WR (t-test: p < 0.001). Monocular visual acuity was 0.0 logMAR in 96% of the tested eyes, when refractive errors were corrected with measurements from AR, indicating that only small differences between the different types of prescriptions are present.
... the horizontal coma exhibited a slight negative shift without significant difference in both groups following LOA correction. These changes were in accordance with Salmon's study, which showed horizontal coma was relatively stable [24]. Vertical coma and spherical aberration showed a positive shift in both groups. ...
... Most myopic eyes (mean SD is −1.579D 0.141) in this study were at low to moderate level; therefore, the spherical aberration presented here was slightly shifted to negative compared to that in high myopic eyes. The mean x-axis coma of the right eye was positive in this study and that was in accordance with previous investigations [24]. ...
Article
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This study investigated the instantaneous changes of higher-order aberrations (HOAs) following lower-order aberrations (LOAs) correction with a closed-loop adaptive optics (AO) system in myopic and emmetropic eyes. Data were analyzed using generalized additive mixed models. Time-related changes in HOAs were modeled with two-piecewise linear regressions and were compared between myopic and emmetropic eyes. Both vertical coma and spherical aberrations shifted to the positive direction immediately after LOA correction. The fluctuations of the above values were significantly faster in myopic than in emmetropic eyes. Understanding these changes in HOAs following LOA correction may help in achieving better visual outcomes.
... The application of fs-lasers in the posterior eye segment still lacks the necessary accuracy, safety and effectiveness. 8 Because of the relatively large aberrations in the human eye, 9 adaptive optics (AO) is indispensable to reduce the laser power for fs-laser treatments close to the light sensitive posterior retina. 10 In traditional AO systems, originally invented for astronomical purposes, a wavefront sensor (e.g. ...
Conference Paper
Surgery with fs-laser in the posterior part of the eye could be useful for separation of tractional epiretinal membrane and vitreous floaters treatment. However, focus degradation occurs near the retina due to induced aberrations by cornea and lens. To overcome this issue, adaptive optics with wavefront sensor and wavefront modulator can be utilized. We demonstrate an alternative concept for image guided femto second laser (fs-laser) surgery in the posterior eye with wavefront sensorless adaptive optics (WFSLAO). Our laboratory setup consists of an 800 nm fs-laser and a superluminescent diode (SLD) with 897.2 nm central wavelength. The SLD is used for optical coherence tomography (OCT) whereby the light for the OCT sample arm and the fs-laser share the same optical path which contains a deformable mirror, scanner and focusing optics. Energy calibrated photodiodes are used to measure the threshold energy for a laser induced optical breakdown inside a water filled chamber that acts as simple eye model. OCT image based metrics were used to determine a set of Zernike polynomials that describe a near optimal deformable mirror state. Such a mirror state improved OCT resolution and at the same time lowered the required fs-laser energy for a laser induced optical breakdown inside the eye model substantially.
... Zernike modes and their common names[12,13] ...
Article
Aim This study investigated the correlation between chalazion, regarding its size, site and location, and different types of refractive errors, as well as high-order aberrations in Egyptian patients. Patients and methods This is a cross-sectional study which compared 53 eyes from 48 patients having eyelid chalazion with 43 eyes of age-matched control group. Chalazion was classified according to size, site, and location. Refraction was done using an autorefractokeratometer. Corneal topography and aberrations were done using a Scheimpflug topographer. Results The third-order aberration (coma Z31) and fourth-order aberration (secondary astigmatism Z42) were higher in the chalazion group compared with the control group (P=0.035 and 0.035, respectively). Lower lid chalazia showed higher Esafoil aberration Z66 than both upper lid and control group (P=0.015 and 0.001, respectively). In addition, the large-sized chalazion group showed a significant increase in Esafoil aberration Z66 than the small-sized group and the control group (P=0.004 and 0.003, respectively). No difference was observed between the chalazion group and the control group regarding autorefractokeratometer data or topographic data. Conclusion Although the presence of chalazion may not be associated with changes in refraction or corneal astigmatism, it still can cause increase in some high-order aberrations and hence, in the quality of vision. Besides, it is a threat as a source of infection before any surgical procedure. Therefore, it is important to exclude and treat any chalazion before proceeding with any refractive surgery especially wave-front-guided and wave-front-optimized corneal refractive procedures.
... [1] The visual function can be measured basically in two ways: quantitatively by visual acuity and qualitatively by aberrometry, through high-order aberrations in Root Mean Square (RMS). [2][3][4][5][6][7][8][9][10] There are many other tests that contribute to the assessment of visual function, such as visual field (which indicates whether the athlete has peripheral vision), Titmus test (which indicates whether there is binocular vision and a sense of depth), and spherical equivalent (equal to the algebraic sum of the value of the sphere + half of the patient's ametropia cylindrical value). Judo is a sport of physical contact and depends on the speed, reflexes, strength, and technique. ...
Article
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Descriptive case series of visual function of high performance judokas.
... Among the different optical and image quality functions, wavefront aberration W is the most extensive way to objectively characterize the optical performance of the human eye. The robustness and reliability of ocular aberrometers, as well as the popularization of commercial systems [1], caused the publication of a high number of both basic [2,3] and clinical studies [4][5][6][7][8]. A number of researchers studied the relationship between W and the most relevant magnitudes used in the clinical practice, such as visual acuity VA [9,10] or refractive error Rx [11]. ...
Article
This work presents a compact statistical model of the retinal image quality in a large population of human eyes following two objectives. The first was to develop a general modal representation of the optical transfer function (OTF) in terms of orthogonal functions and construct a basis composed of cross-correlations between pairs of complex Zernike polynomials. That basis was not orthogonal and highly redundant, requiring the application of singular value decomposition (SVD) to obtain an orthogonal basis with a significantly lower dimensionality. The first mode is the OTF of the perfect system, and hence the modal representation, is highly compact for well-corrected optical systems, and vice-versa. The second objective is to apply this modal representation to the OTFs of a large population of human eyes for a pupil diameter of 5 mm. This permits an initial strong data compression. Next, principal component analysis (PCA) is applied to obtain further data compression, leading to a compact statistical model of the initial population. In this model each OTF is approximated by the sum of the population mean plus a linear combination of orthogonal eigenfunctions (eigen-OTF) accounting for a selected percentage (90%) of the population variance. This type of models can be useful for Monte Carlo simulations among other applications.
... [1][2][3] In addition to the well-documented ocular chromatic aberrations, 4,5 the human eye has many higher-order monochromatic aberrations, with spherical aberration, coma, and trefoil being the largest in most eyes. 6,7 Measurement and correction of these higher-order aberrations are now an important component of many refractive corrections; for example, both intraocular lenses and contact lenses now specifically include aspheric surfaces to control spherical aberration, [8][9][10] aberration reducing corrections offer great advantages for eyes with keratoconus, [11][12][13][14] and refractive surgery has attempted to correct the full suite of aberrations. 15,16 Recently, zonal 17 and aspheric 18 soft contact lenses have also been used with the aim to slow the progression of myopia, where measures of onaxis 10 or off-axis 19 optics are necessary. ...
Article
Significance: Measurement of ocular aberrations is a critical component of many optical corrections. Purpose: This study examines the accuracy and repeatability of a newly available high-resolution pyramidal wavefront sensor-based aberrometer (Osiris by Costruzione Strumenti Oftalmici, Firenze, Italy). Methods: An engineered model eye and a dilated presbyopic eye were used to assess accuracy and repeatability of aberration measurements after systematic introduction of lower- and higher-order aberrations with calibrated trial lenses (sphere +10.00 to -10.00 D, and astigmatic -4.00 and -2.00 D with axis 180, 90, and 45°) and phase plates (-0.57 to 0.60 μm of Seidel spherical aberration defined over a 6-mm pupil diameter). Osiris aberration measurements were compared with those acquired on a previously calibrated COAS-HD aberrometer for foveal and peripheral optics both with and without multizone dual-focus contact lenses. The impact of simulated axial and lateral misalignment was evaluated. Results: Root-mean-square errors for paraxial sphere (corneal plane), cylinder, and axis were, respectively, 0.07, 0.11 D, and 1.8° for the engineered model and 0.15, 0.26 D, and 2.7° for the presbyopic eye. Repeatability estimates (i.e., standard deviation of 10 repeat measures) for the model and presbyopic eyes were 0.026 and 0.039 D for spherical error. Root-mean-square errors of 0.01 and 0.02 μm, respectively, were observed for primary spherical aberration and horizontal coma (model eye). Foveal and peripheral measures of higher- and lower-order aberrations measured with the Osiris closely matched parallel data collected with the COAS-HD aberrometer both with and without dual-focus zonal bifocal contact lenses. Operator errors of focus and alignment introduced changes of 0.018 and 0.02 D/mm in sphere estimates. Conclusions: The newly available clinical pyramidal aberrometer provided accurate and repeatable measures of lower- and higher-order aberrations, even in the challenging but clinically important cases of peripheral retina and multifocal optics.
... Chia et al. 152 reported a change in photopic pupil size with 0.01%, 0.1% and 0.5% atropine from a baseline of~4.7 mm to 5.8, 7.4 and 7.9 mm, respectively. Based on the polynomial regression reported by Salmon and van de Pol, 153 HOA RMS would have increased by~0.14, 0.43 and 0.54 μm due to the pupil dilation associated with 0.01%, 0.1% and 0.5% atropine, respectively. Therefore, the change in HOA RMS resulting from pupil mydriasis is significantly greater than the change in HOAs resulting from the cycloplegic hyperopic shift. ...
Article
Evidence from animal and human studies suggests that ocular growth is influenced by visual experience. Reduced retinal image quality and imposed optical defocus result in predictable changes in axial eye growth. Higher order aberrations are optical imperfections of the eye that alter retinal image quality despite optimal correction of spherical defocus and astigmatism. Since higher order aberrations reduce retinal image quality and produce variations in optical vergence across the entrance pupil of the eye, they may provide optical signals that contribute to the regulation and modulation of eye growth and refractive error development. The magnitude and type of higher order aberrations vary with age, refractive error, and during near work and accommodation. Furthermore, distinctive changes in higher order aberrations occur with various myopia control treatments, including atropine, near addition spectacle lenses, orthokeratology and soft multifocal and dual‐focus contact lenses. Several plausible mechanisms have been proposed by which higher order aberrations may influence axial eye growth, the development of refractive error, and the treatment effect of myopia control interventions. Future studies of higher order aberrations, particularly during childhood, accommodation, and treatment with myopia control interventions are required to further our understanding of their potential role in refractive error development and eye growth.
... These tissues are made up of cells that grow into place during development, and since such biological processes cannot always form perfectly, the lens and cornea do not mature with an optically ideal shape. Indeed, human eyes manifest particular lower and higher order monochromatic aberrations caused by irregularities in shape and refractive power of these structures [38]. Rays of light traversing the eye will thus be refracted irregularly, causing optical distortions that ultimately limit the quality of the retinal image. ...
Chapter
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Photoreceptors in the retina constitute the cellular building blocks of the initial stage of vision. To isolate the contribution of a single cell to any percept is quite challenging because normal ocular optics and motion distributes light from small stimuli over many photoreceptors. Recent microstimulation techniques coupled with adaptive optics scanning laser ophthalmoscopy can produce stimuli as small as single photoreceptors that can be directed to precise locations on the retina. This enables direct in vivo study of cone activity and how it relates to visual perception. We provide an overview of the technology and recent results obtained with cone-targeted psychophysics.
... Despite high inter-subject variability, average values reported here about Fabry patient's CRF were found similar to those of a non-Fabry population (NFP = 10.5 mmHg) [73,74]. [75]. This cohort of patients showed lower values, then not generating visual symptoms. ...
Preprint
Full-text available
Purpose This study aims to assess the evolution of ocular manifestations in a cohort of Fabry patients. METHODS This is a prospective observational study conducted from 2013 to 2017 (5 consecutive exams). All subjects underwent a comprehensive ocular examination including oriented case history, refraction, corneal topography, biomechanical corneal properties and pachometry assessments, aberrometry, anterior segment evaluation, double-frequency visual field (FDT), intra-ocular pressure, and ocular fundus. At baseline, 41 subjects enrolled but 9 dropped-out and 4 files were not kept for analysis (missing data). Remaining 28 subjects were classified into: Group 1 -hemizygotes (HMZ), all on enzyme replacement therapy (ERT) (N=10); Group 2 -heterozygotes (HTZ) actively ERT-treated (N=8), and Group 3 -HTZ not treated (N=10). RESULTS There is a high intra and inter-subjects variability. At baseline, prevalence of the ocular manifestations found is similar to published data: cornea verticillata (89.2%), conjunctival vessels tortuosity (85.7%), corneal haze (67.8%), retinal vessels tortuosity (64.2%), anterior cataract (39.2%) and posterior cataract (28.5%). Prevalence for new elements are found: upper lid vessels toricity (96.4%) and micro-aneurysms (42.8%). At the end, micro-aneurysms (+82%), posterior cataract (+75%) corneal haze (+21%) anterior cataract (+17%) and retinal vessels tortuosities (+4%) evolved in prevalence and severity despite the fact that 68% of the patients were on ERT. Treated heterozygotes evolved more than other groups (p>0.05) CONCLUSION ERT does not halt the clinical evolution of several ocular manifestations. Longer observational time may be required to fully confirm these findings.
... Despite high inter-subject variability, average values reported here about Fabry patient's CRF were found similar to those of a non-Fabry population (NFP = 10.5 mmHg) [73,74]. [75]. This cohort of patients showed lower values, then not generating visual symptoms. ...
Article
Full-text available
Purpose: This study aims to assess the evolution of ocular manifestations in a cohort of Fabry patients. Methods: This is a prospective observational study conducted from 2013 to 2017 (5 consecutive exams). All subjects underwent a comprehensive ocular examination including oriented case history, refraction, corneal topography, biomechanical corneal properties and pachometry assessments, aberrometry, anterior segment evaluation, double-frequency visual field (FDT), intra-ocular pressure, and ocular fundus. At baseline, 41 subjects enrolled but 9 dropped-out and 4 files were not kept for analysis (missing data). Remaining 28 subjects were classified into: Group 1 -hemizygotes (HMZ), all on enzyme replacement therapy (ERT) (N = 10); Group 2 -heterozygotes (HTZ) actively ERT-treated (N = 8), and Group 3 -HTZ not treated (N = 10). Results: There is a high intra and inter-subjects variability. At baseline, prevalence of the ocular manifestations found is similar to published data: cornea verticillata (89.2%), conjunctival vessels tortuosity (85.7%), corneal haze (67.8%), retinal vessels tortuosity (64.2%), anterior cataract (39.2%) and posterior cataract (28.5%). Prevalence for new elements are found: upper lid vessels toricity (96.4%) and micro-aneurysms (42.8%). At the end, micro-aneurysms (+82%), posterior cataract (+75%) corneal haze (+21%) anterior cataract (+17%) and retinal vessels tortuosities (+4%) evolved in prevalence and severity despite the fact that 68% of the patients were on ERT. Treated heterozygotes evolved more than other groups (p>0.05). Conclusion: ERT does not seem to halt the clinical evolution of several ocular manifestations. Longer observational time and objective grading systems may be required to fully confirm these findings.
... We provide a comprehensive analysis of the optical properties of the tree shrew eye and some comparison with other species but note that there are limitations in the current study that may guide future (Geng et al., 2011), tree shrew and human (Salmon and van de Pol, 2006). (B) Radially-averaged MTF for tree shrews (n = 11 eyes) and humans (n = 74 eyes (Cheng et al., 2004)) for a 4 mm pupil. ...
Article
Tree shrews are small mammals with excellent vision and are closely related to primates. They have been used extensively as a model for studying refractive development, myopia, and central visual processing and are becoming an important model for vision research. Their cone dominant retina (∼95% cones) provides a potential avenue to create new damage/disease models of human macular pathology and to monitor progression or treatment response. To continue the development of the tree shrew as an animal model, we provide here the first measurements of higher order aberrations along with adaptive optics scanning light ophthalmoscopy (AOSLO) images of the photoreceptor mosaic in the tree shrew retina. To compare intra-animal in vivo and ex vivo cone density measurements, the AOSLO images were matched to whole-mount immunofluorescence microscopy. Analysis of the tree shrew wavefront indicated that the optics are well-matched to the sampling of the cone mosaic and is consistent with the suggestion that juvenile tree shrews are nearly emmetropic (slightly hyperopic). Compared with in vivo measurements, consistently higher cone density was measured ex vivo, likely due to tissue shrinkage during histological processing. Tree shrews also possess massive mitochondria ("megamitochondria") in their cone inner segments, providing a natural model to assess how mitochondrial size affects in vivo retinal imagery. Intra-animal in vivo and ex vivo axial distance measurements were made in the outer retina with optical coherence tomography (OCT) and transmission electron microscopy (TEM), respectively, to determine the origin of sub-cellular cone reflectivity seen on OCT. These results demonstrate that these megamitochondria create an additional hyper-reflective outer retinal reflective band in OCT images. The ability to use noninvasive retinal imaging in tree shrews supports development of this species as a model of cone disorders.
... Manifest refraction can correct for most of the low-order aberrations, leaving behind the high-order optical aberrations [20][21][22]. Normal eyes have on average a root-mean-square (RMS) error of 0.33 μm for high-order aberrations at a pupil size of 6 mm [23]. This is equivalent to 0.25D of defocus. ...
Article
Full-text available
Background Many patients voice concerns regarding poor night vision, even when they see 20/20 or better in the exam room. During mesopic and scotopic conditions the pupil size increases, increasing the effects on visual performance of uncorrected (residual) refractive errors. The i.Scription refraction method claims to optimize traditional refractions for mesopic and scotopic conditions, by using the information that the Zeiss i.Profilerplus gathers of ocular aberrations (low and high order). The aim of this study was to investigate any differences between habitual and i.Scription refractions and their relationship to night vision complaints. Methods Habitual, subjective, and i.Scription refractions were obtained from both eyes of eighteen subjects. Low and high order aberrations of the subjects were recorded with the Zeiss i.Profilerplus. The root mean square (RMS) metric was calculated for small (3 mm) and maximum pupil sizes. Subjects rated their difficulty with driving at night on a scale of 1–10. Results There was a statistically significant difference between the habitual and i.Scription refractions on both the sphere and cylinder values [(t = 3.12, p < 0.01), (t = 5.39, p < 0.01)]. The same was found when comparing the subjective and i.Scription refractions [(t = 2.31, p = 0.03), (t = 2.54, p = 0.02)]. There were no significant differences found when comparing the sphere and cylinder values between the habitual and subjective refractions or on any combination of spherical equivalent refraction. The maximum pupil size of the subject population on this study, measured with the i.Profilerplus, was 4.8 ± 1.04 mm. Ten out of the eighteen subjects had discomfort at night with an average magnitude of 4 ± 2.7. Ratings of difficulty with night vision correlated with the change in spherical equivalent correction between the habitual and i.Scription refractions (p = 0.01). A sub-analysis of myopic subjects (n = 15) showed an increase in the significance of this relationship (p = 0.002). Conclusions The i.Scription method improves night vision by correcting the sphere and cylinder more precisely. There was a correlation between the amount of change in the cylinder value between habitual and i.Scription prescriptions and the magnitude of the reported visual discomfort at night. Electronic supplementary material The online version of this article (10.1186/s12886-019-1053-x) contains supplementary material, which is available to authorized users.
... Despite high inter-subject variability, average values reported here about Fabry patient's CRF were found similar to those of a non-Fabry population (NFP = 10.5 mmHg) [73,74]. [75]. This cohort of patients showed lower values, then not generating visual symptoms. ...
Article
Full-text available
Purpose: This study aims to assess the evolution of ocular manifestations in a cohort of Fabry patients. Methods: This is a prospective observational study conducted from 2013 to 2017 (5 consecutive exams). All subjects underwent a comprehensive ocular examination including oriented case history, refraction, corneal topography, biomechanical corneal properties and pachometry assessments, aberrometry, anterior segment evaluation, double-frequency visual field (FDT), intra-ocular pressure, and ocular fundus. At baseline, 41 subjects enrolled but 9 dropped-out and 4 files were not kept for analysis (missing data). Remaining 28 subjects were classified into: Group 1 -hemizygotes (HMZ), all on enzyme replacement therapy (ERT) (N=10); Group 2 -heterozygotes (HTZ) actively ERT-treated (N=8), and Group 3 -HTZ not treated (N=10). Results: There is a high intra and inter-subjects variability. At baseline, prevalence of the ocular manifestations found is similar to published data: cornea verticillata (89.2%), conjunctival vessels tortuosity (85.7%), corneal haze (67.8%), retinal vessels tortuosity (64.2%), anterior cataract (39.2%) and posterior cataract (28.5%). Prevalence for new elements are found: upper lid vessels toricity (96.4%) and micro-aneurysms (42.8%). At the end, micro-aneurysms (+82%), posterior cataract (+75%) corneal haze (+21%) anterior cataract (+17%) and retinal vessels tortuosities (+4%) evolved in prevalence and severity despite the fact that 68% of the patients were on ERT. Treated heterozygotes evolved more than other groups (p>0.05) Conclusion: ERT does not seem to halt the clinical evolution of several ocular manifestations. Longer observational time and objective grading systems may be required to fully confirm these findings.
... [1][2][3] In addition to the well-documented ocular chromatic aberrations, 4,5 the human eye has many higher-order monochromatic aberrations, with spherical aberration, coma, and trefoil being the largest in most eyes. 6,7 Measurement and correction of these higher-order aberrations are now an important component of many refractive corrections; for example, both intraocular lenses and contact lenses now specifically include aspheric surfaces to control spherical aberration, [8][9][10] aberration reducing corrections offer great advantages for eyes with keratoconus, [11][12][13][14] and refractive surgery has attempted to correct the full suite of aberrations. 15,16 Recently, zonal 17 and aspheric 18 soft contact lenses have also been used with the aim to slow the progression of myopia, where measures of onaxis 10 or off-axis 19 optics are necessary. ...
Conference Paper
Purpose: Aberrometry is a key tool for evaluating technological advances in eye care, e.g. wavefront-guided refractive surgery. However, the widely used high sampling density COAS HD aberrometer (Wavefront Sciences Inc.) is no longer available. We examined the accuracy and repeatability of a newly developed high sampling density (41μm lens diameter) clinical aberrometer (Osiris, CSO, Italy). Methods: Using the Osiris model eye and a dilated presbyopic eye, trial lenses were introduced (sphere +12 to -10 D, and astigmatic -4 and -2 D with axis 180, 90 and 45) to calibrate assessment of lower order aberrations. Simulated operator errors of axial and lateral alignment and patient errors of fixation were evaluated. Repeatability of lower and higher order aberrations (LOA & HOA) was assessed (n = 10) for the model eye without realignment, with the presbyopic model eye with realignment between each measure. Five young patient eyes were tested with both Osiris and COAS HD without any correction, with their spectacle correction, and when fit with a single vision and a multifocal contact lens. Results: Observed spherical Rx of model and presbyopic eye viewing through a series of spherical trial lenses were on average (Root Mean Square Error, RMSE) within 0.17D of expected. Linear models fit to the observed vs. expected plots reveal slopes of 0.985 and 0.97, with intercepts of -0.13D and -0.01D for the model and presbyopic eyes, respectively. In each case R2 exceeded 0.99. Measured RMSE for the cylindrical lens series was 0.011D of power and 0.18 deg of axis error. Repeatability estimates (SD of 10 repeat measures) for the model and presbyopic eyes were 0.026D and 0.039D for spherical Rx. Repeat measures of HOAs were identical for the model eye, and SDs for primary spherical aberration, vertical and horizontal coma, and overall higher order aberration RMS were 0.013 μm, 0.019 μm, 0.03 μm, and 0.018 μm, respectively. Operator errors of focus introduced Rx changes of 0.018 D/mm, while maximum (1.5 mm) alignment errors introduced 0.11D change in sphere estimate. Observer fixation errors (range +/- 6 deg) introduced modest changes in LOA & HOA, most significantly, horizontal fixation errors systematically modified horizontal coma. When testing young adult eyes with a range of refractive corrections Osiris and COAS measurements analyzed over a 5mm pupil diameter produced highly correlated results with R2 = 0.91, 0.84 and 0.83, and regression slopes of 0.97, 0.98, and 0.89, respectively, for C4,0, C3,-1, and C3,1. Conclusion: The Osiris clinical aberrometer provided accurate and repeatable measures of spherical refractive error over the -10 to +5 D range and astigmatism up to 4D. Operator-initiated alignment errors were <0.1D for LOA and 0.01μm for HOAs. Patient fixation errors introduced modest (<0.25 D) errors in Rx but systematic changes in coma. The COAS and Osiris produced very similar measured aberrations with several types of correcting lens.
... The optical quality of the eye has been studied in increasing detail and complexity from geometric schematic eyes [1,2] and dioptric refractive error [3,4], to optical metrics such as line spread functions [5][6][7], point spread functions (PSFs) [8,9], modulation transfer functions (MTFs) [10][11][12][13][14], root mean square (RMS) wavefront error (WFE) [14][15][16], and metrics of retinal image quality [17][18][19][20]. ...
Article
The visual image quality metric the visual Strehl ratio (VSX) combines a comprehensive description of the optics of an eye (wavefront error) with an estimate of the photopic neural processing of the visual system, and has been shown to be predictive of subjective best focus and well correlated with change in visual performance. Best-corrected visual image quality was determined for 146 eyes, and the quantitative relation of VSX, age, and pupil size is presented, including 95% confidence interval norms for age groups between 20 and 80 years and pupil diameters from 3 to 7 mm. These norms were validated using an independently collected population of wavefront error measurements. The best visual image quality was found in young eyes at smaller pupil sizes. Increasing pupil size caused a more rapid decrease in VSX than increasing age. These objectively determined benchmarks represent the best theoretical levels of visual image quality achievable with a sphere, cylinder, and axis correction in normal eyes and can be used to evaluate both traditional and wavefront-guided optical corrections provided by refractive surgery, contact lenses, and spectacles.
... Indeed, we identified that a horizontal motion, in conjunction with the presence of spherical aberration, produces a fluctuation of a 8 (see Fig. 6). It turns out that average static spherical aberration measured on our population is slightly positive (a st at 11 = 0.06µm ± 0.05µm), which was also observed by Salmon et al. [23]. We then conclude that a moderate part of a 8 dynamics is due to pupil motion; ...
Article
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To evaluate the contribution of fixational eye movements to dynamic aberration, 50 healthy eyes were examined with an original custom-built Shack-Hartmann aberrometer, running at a temporal frequency of 236Hz, with 22 lenslets across a 5mm pupil, synchronized with a 236Hz pupil tracker. A comparison of the dynamic behavior of the first 21 Zernike modes (starting from defocus) with and without digital pupil stabilization, on a 3.4s sequence between blinks, showed that the contribution of fixational eye movements to dynamic aberration is negligible. Therefore we highlighted the fact that a pupil tracker coupled to an Adaptive Optics Ophthalmoscope is not essential to achieve diffraction-limited resolution.
... In previous research, reference values for adult eyes have been established by either directly measuring a large population of normal vision adults 3,4 or by collecting data from multiple sites and using this information to calculate the reference values. 6 However, these values could not be used as references for children because higher-order aberrations vary with age. 12,13 For example, Bisneto 19 measured higherorder aberrations of 312 eyes of people whose ages ranged from 7 to 62 years, and the results revealed that there was a positive relationship between age and higher-order aberrations. ...
Article
Full-text available
Significance: This study provides a descriptive characterization of higher-order optical aberrations for the eyes of a larger number of Chinese children and adolescents. Purpose: To determine the distribution of higher-order aberrations (HOAs) of Han Chinese young subjects with normal vision and their relationship to age. Methods: Children and adolescents, aged from 3 to 17 years, with normal visual acuity were enrolled, and their wavefront aberrations for a 6-mm pupil were evaluated by the Zywave II aberrometer. Their correlations with age were analyzed, and the 95% statistical reference ranges were computed for each Zernike term. Results: A total of 1634 eyes (287 for preschool-age children, 897 for school-age children, and 450 for adolescents) were analyzed. There was a significant correlation with age and the root mean square (RMS) of total HOAs (r = 0.256, P < .0001), third-order aberrations (r = 0.062, P = .029), fourth-order aberrations (r = 0.197, P < .0001), fifth-order aberrations (r = 0.067, P = .017), and trefoil-like aberrations (r = 0.100, P < .0001) in the myopic group. There were significant differences in RMS values (except coma-like aberrations, χ = 4.179, P = .124) as well as the Zernike coefficients among three different age groups. Therefore, the 95% statistical normal reference values were calculated separately for three age groups. Conclusions: The RMS value of total HOAs, coma-like, trefoil-like, third-order, fourth-order, and fifth-order aberrations are correlated with age, and the RMS values and Zernike coefficients of aberrations were different in different age stages of the subjects. This study described the distribution of HOAs in children and adolescents and established 95% statistical normal values of HOAs for different ages of children and adolescents by analyzing the HOAs in a large number of the Han Chinese clinical population.
... (To quantify them, the decomposition according to Zernike is widely used in ophthalmic optics, using terms like coma, trefoil, spherical aberration, and astigmatism II.) They are important to consider, since human eyes show significant amounts of higher order aberrations, that differ among individuals 11 and can be dealt with. ...
... However, when preoperative HOA RMS was >0.3 µm, the WFG treatment had a greater advantage in reducing preexisting HOA RMS. This cutoff value of 0.3 µm was based on several reports that concluded that the average HOA RMS value in a normal population was around 0.3 µm [15,22,23]. In contrast, other researchers have insisted that HOA RMS differs according to ethnicity [24][25][26]. ...
Article
Full-text available
Purpose: To compare the visual outcomes and corneal aberrations between wavefront-optimized (WFO) and corneal wavefront-guided (WFG) photorefractive keratectomy (PRK) in low to moderate myopia. Methods: Twenty-seven eyes treated with WFO and 29 eyes treated with WFG PRK using a Schwind Amaris 750S Excimer laser were included after 6 months of postoperative follow-up. Uncorrected distance visual acuity, corrected distance visual acuity, refractive errors, corneal higher-order aberrations (HOA) and corneal thickness obtained using a Scheimpflug system, and central ablation depth and volume were evaluated during the preoperative period and again at the postoperative 6-month visits. Results: Postoperatively, uncorrected distance visual acuity, corrected distance visual acuity, manifest spherical equivalent, and refractive astigmatism were improved in both groups, and there was no statistically significant difference between the two groups. There was no significant difference in safety, efficacy, or predictability of the refractive outcome. Postoperative total corneal HOA root mean square (RMS), coma RMS, and spherical aberration were significantly increased in both groups. Among these, only spherical aberration showed a significant difference between the two groups, with greater increase in the WFO group at 6 months postoperatively. The changes in corneal HOA RMS and spherical aberration were smaller in the WFG group, and this benefit was marked in eyes with high HOA RMS (≥0.4 μm) and spherical aberration (≥0.2 μm). Even though ablation volume in the WFG group was much larger than that of the WFO group, there was no significant difference in postoperative central and peripheral corneal thickness between the two groups. Conclusions: Both WFO and WFG PRK using a Schwind Amaris 750S laser for low to moderate myopia were safe and effective at improving visual and refractive outcomes. However, WFG PRK induced fewer spherical aberrations than WFO PRK and may be more advantageous for eyes with high HOA root mean square or spherical aberration.
... Several methods have been developed to analyze the quality of human cornea in the ophthalmology research, such as optical coherence tomography [18][19][20][21] and Shack-Hartmann wavefront sensor [22,23]. The mathematical results from the Shack-Hartmann wavefront sensor measurements can be expanded by the Zernike polynomials [24,25] and used to describe the aberrations. ...
Article
Full-text available
The blindness caused by cornea diseases has exacerbated many patients all over the world. The disadvantages of using donor corneas may cause challenges to recovering eye sight. Developing artificial corneas with biocompatibility may provide another option to recover blindness. The techniques of making individual artificial corneas that fit the biometric parameters for each person can be used to help these patients effectively. In this study, artificial corneas with different shapes (spherical, aspherical, and biconic shapes) are designed and they could be made by two different hydrogel polymers that form an interpenetrating polymer network for their excellent mechanical strength. Two designed cases for the artificial corneas are considered in the simulations: to optimize the artificial cornea for patients who still wear glasses and to assume that the patient does not wear glasses after transplanting with the optimized artificial cornea. The results show that the artificial corneas can efficiently decrease the imaging blur. Increasing asphericity of the current designed artificial corneas can be helpful for the imaging corrections. The differences in the optical performance of the optimized artificial corneas by using different materials are small. It is found that the optimized artificial cornea can reduce the high order aberrations for the second case.
... For example, compiled statistics from one study of 2560 human eyes show that, of all high-order aberration terms, only spherical aberration was found to be non-zero. 28 The small positive spherical aberration reported in the aforementioned study was similar to our finding in the guinea pig eye (0.0481 ± 0.077). Although none of our data reached statistical significance, this may reflect the small number of guinea pig eyes included in the current study. ...
Article
Full-text available
Purpose: The guinea pig is widely used in studies of refractive error development and myopia which often involve experimental optical manipulations. The study described here investigated the optical quality of the guinea pig eye, for which there are limited data, despite its fundamental importance to understanding visually guided eye growth. Methods: The ocular aberrations of eight adolescent New Zealand pigmented guinea pigs (6-11 weeks old) were measured after cycloplegia using a custom-built Shack-Hartmann aberrometer and fit with a Zernike polynomial function to the 10th order (65 terms). The optical quality of their eyes was assessed in terms of individual Zernike coefficients, and data were further analyzed to derive root-mean-square (RMS) wavefront errors, modulation transfer functions (MTFs), point spread functions (PSFs), Strehl ratios, and depth of focus. A 4-mm pupil was used in all computations. The derived data are compared with equivalent data from normal young adult human eyes. Results: The guinea pigs exhibited low hyperopia and a small amount of positive spherical aberration, with other aberration terms decreasing with increasing order. Their average depth of focus, estimated from through-focus modulation, was 3.75 diopters. The RMS wavefront error of the guinea pig eye was found to be larger than that of the human eye for the same pupil size, reflecting a higher degree of aberrations, although the PSF (area) on the retina was smaller and sharper due to its shorter focal length. The radial average best-focus MTF derived for the guinea pig eye showed good performance at very low spatial frequencies, with a steeper decline with increasing frequency than for the human eye, dropping below 0.3 at 9 cpd. When converted to linear units (cycles/mm), the guinea pig eye had a higher spatial frequency cutoff and a slight contrast advantage for low spatial frequencies compared to the human eye. Conclusions: The optical quality of the guinea pig eye is far superior to their reported behavioral visual acuity. This implies a neuroanatomical limit to their vision, which contrasts with the close match of optical and neural limits to spatial resolution in human eyes. The significance for eye growth regulation of the relative optical advantages exhibited by guinea pig eyes, when optical quality is expressed in linear rather than angular retinal units, warrants further consideration.
... Nonetheless, because the onset and progression of such large differences in refraction between the two eyes is not clearly known, the choice of the age at surgery and accurate interpretation of the refractive stability after refractive surgery is always biased by the possible age-related refractive changes in that particular age group. Orthokeratology (OK) lenses are rigid contact lenses with a reverse geometry on the posterior surface [30,31]. Overnight wear of the lens flattens the central cornea zone and increases the relative corneal refractive power in the periphery. ...
Article
Full-text available
Introduction: This study aimed to investigate the therapeutic effects of overnight orthokeratology (OK) lenses on anisometropes. Methods: We enrolled 178 anisometropes from August 2015 to August 2017. We then divided these patients into 2 parts depending on them wearing either monocular or binocular OK lenses. In part one, 47 monocular myopic subjects (25 males and 22 females) were treated with OK lenses in the myopic eyes only. We also labeled the myopic eyes as the OK group and the contralateral nonmyopic eyes as the control group. The initial average wearing age of the subjects was 12.35 ± 2.37 years (8-16 years). The mean follow-up duration was 15.43 ± 4.88 months (7-25 months). The average spherical equivalent refraction (SER) was -2.31 ± 1.16 diopter (D) in the OK group and 0.15 ± 0.49 D in the control group (p < 0.001). In part 2, 131 binocular myopic anisometropes (56 males and 75 females) were involved in the study. The eyes with more severe myopia were assigned to the G group and the contralateral eyes to the L group. The initial average wearing age of the subjects was 12.92 ± 2.60 years ( 8-16 years). The mean follow-up duration was 17.83 ± 5.02 months (7-26 months). The average SER was -4.79 ± 1.90 D in the G group and -3.14 ± 1.88 D in the L group (p < 0.001). We calculated the axial length (AL) difference and AL elongation as our primary outcome measures. Results: In part one, the AL elongation in the OK group (0.21 ± 0.09 mm) was significantly lower than that in the control group (0.70 ± 0.17 mm) at 24 months (p < 0.001). Meanwhile, the AL difference exhibited a decrease of 0.50 ± 0.29 mm from a baseline of 1.08 ± 0.35 to 0.58 ± 0.25 mm at 24 months (F = 24.539, p < 0.001). In part 2, the AL had increased by 0.17 ± 0.13 mm in the G group and 0.24 ± 0.18 mm in the L group after 24-month follow-up, respectively (p < 0.001). While the AL difference decreased from 0.55 ± 0.11 mm at the baseline, to 0.48 ± 0.08 mm at 24 months, eliciting a decrement in AL difference of 0.07 ± 0.09 mm (F = 3.884, p = 0.030). Conclusions: OK lenses can slow down AL growth in anisometropes and has a greater effect on reducing AL elongation in the more severely affected myopic eyes of anisometropic patients.
... An orthokeratology lens is a rigid contact lens with a reverse geometry on its back surface [15,16] . ...
Preprint
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Background: To Investigate the efficacy of overnight orthokeratology (Ortho-k) for myopia control and the relationship between axial length (AL) changes and different baseline factors. Methods: This is a retrospective study of 675 myopic patients (Affiliated Eye Hospital of Shandong University of TCM) who received Ortho-k correction between August 2015 and July 2017. These subjects were followed up at least for 12 months. Genders, age, parental refractive status, manifest refractions, cycloplegic refractions, uncorrected and best-corrected visual acuities, power vector of astigmatism, corneal curvature, age at initiation of Ortho-k wear (year), intraocular pressuren (IOP), anterior chamber depth (ACD), pupil size (PL), corneal diameter (CD) and AL were obtained for analysis. Correlation and multivariate logistic regression analyses were used to screen for the factors that can improve treatment outcome. Results: The baseline 675 patients’ AL of was 25.12±1.00 mm, and after 12 months of treatment, the AL was 25.30±0.94 mm, and the axial elongation was 0.18±0.22 mm. Univariate analysis of the right-eye independent variable of 675 patients showed a statistically significant association between age at initiation of Ortho-k wear, spherical equivalent refractive (SER), and changes in AL. Regression analysis results show that age at initiation of Ortho-k wear and SER are independent factors with effects on the treatment outcome. Conclusion: Ortho-k was effective in slowing myopia progression over a one-year follow-up period. Age at initiation of Ortho-k wear, and SER were found to be associated with increased change of AL during follow-up.
Article
Purpose In order to better understand the optical consequence of residual aberrations during conventional rigid contact lens wear in keratoconus, this study aimed to quantify the visual interaction between positive vertical coma (C(3, −1)) and other individual 2nd to 5th radial order Zernike aberration terms. Methods The experiment proceeded in two parts. First, two levels of C(3, −1) (target term) were simulated. Individual Zernike aberration terms from the 2nd to 5th radial orders (test terms) were combined in 0.05‐µm steps a) from −2.00 µm to +2.00 µm with +1.00 µm of C(3, −1) and b) from −1.00 µm to +1.00 µm with +0.50 µm of C(3, −1). The resulting combinations were used to calculate the logarithm of the visual Strehl ratio (logVSX) and predict the relative beneficial or deleterious impact of the interaction. Second, for test terms where an interaction was predicted to provide more than a 0.25 logVSX benefit compared to C(3, −1) alone, high contrast logMAR acuity charts were constructed (simulating the manner in which the test + target term combinations would impact the retinal image of the chart), and randomly read by three well‐corrected, typically‐sighted individuals through a 3.0‐mm diameter artificial pupil. Results When combined with positive C(3, −1), C(3, −3), C(4, −4), C(5, −5), C(5, −3), and C(5, −1) exhibited better visual image quality compared with C(3, −1) alone. Ratios of the test terms to target term providing maximal benefit remained constant for both +0.50 µm and +1.00 µm of C(3, −1). C(3, −3) and C(5, −1) had the largest predicted beneficial effect, with the maximal effect for +1.00 µm of C(3, −1) occurring with +0.35 µm of C(5, −1) and −1.00 µm of C(3, −3). When individuals read letter charts convolved with the point spread function derived from C(3, −1) combined with C(3, −3) and C(3, −1) combined with C(5, −1), the maximal beneficial effect was 0.27 logMAR (13.5 letters) for C(3, −3) and 0.36 logMAR (18 letters) for C(5, −1). Conclusions While most interactions reduced visual image quality, combinations of C(3, −3) (vertical trefoil) and C(5, −1) (vertical secondary coma) provided a clinically relevant beneficial effect in the presence of C(3, −1) (vertical coma) which was demonstrated in both through‐focus simulation and chart reading tests. Future work will examine whether these effects persist in the presence of the entire spectrum of residual aberrations seen in the eyes of individuals with keratoconus.
Article
An adaptive optics visual simulator (AOVS) with an extended dioptric range was developed, allowing measuring and correcting aberrations in a majority of highly ametropic eyes. In the instrument, a tunable lens is used for defocus correction, while a liquid-crystal-on-silicon spatial light modulator is used for compensating or inducing any other aberration. The instrument incorporates a digital projector, which uses a micromirror array to display the stimuli. A motorized diaphragm enables operation for any physiological pupil size. A full description of the instrument and its calibration are provided, together with the results obtained in seven highly myopic subjects with refraction of −7.2 1.8 D (mean SD). Refraction obtained with the instrument was compared to the standard refraction prescribed by trial lenses. When using the refraction obtained by the AOVS, the visual acuity (VA) exhibited an average increase of 0.21 (decimal scale). The visual impact of correcting high-order aberrations is presented in three subjects, whose VAs slightly improved with the correction. High myopes are able to benefit from the improved refraction assessment. The new instrument creates a possibility for a wide number of new experiments, especially for eyes exhibiting large refractive errors, where previous AO instruments failed to operate.
Article
Significance: A base-down prism was incorporated on the anterior surface of rigid-gas-permeable (RGP) contact lenses to explore potential effects on the residual ocular aberrations after contact lens fitting in keratoconic eyes. Purpose: To evaluate the correction of ocular aberrations with corneal prismatic RGP contact lenses in keratoconic eyes and their impact on visual function. Methods: A cross-sectional and randomized study was performed. Seventeen eyes of 17 keratoconus patients (34.6 ± 11.1 years) were evaluated. Two designs (standard and prismatic) of a corneal RGP contact lens (KAKC) were fitted to the same eye of each patient in erandom order: a standard rigid-gas-permeable contact lens as control and a prismatic RGP contact lens with a base-down prism of 1.6 prism diopters. Ocular aberrations were measured for a pupil diameter of 3 mm with and without both contact lenses, while high-contrast distance visual acuity, low-contrast distance visual acuity, and contrast sensitivity were measured under photopic and mesopic conditions. Results: Both contact lenses improved oblique primary astigmatism, defocus, vertical coma, coma-like, and RMS higher-order aberrations compared with the unaided eyes (P < .05). Besides, the prismatic RGP contact lenses offered lower values of vertical coma and RMS higher-order aberrations than the standard rigid-gas-permeable contact lenses (P < .05). Both designs (standard and prismatic) produced a positive vertical coma of lower magnitude than the negative vertical coma of the unaided eyes. On the other hand, the improvement achieved in all visual function variables was the same for both contact lens designs (P ≥ .05). Conclusions: The prismatic RGP contact lenses corrected higher levels of higher-order aberrations compared with the standard rigid-gas-permeable contact lenses. However, both contact lens designs with the same refractive power were equally efficient at improving visual function.
Article
Purpose Contrast sensitivity (CS) has been proposed as a potential method for patients to assess their vision at home. The CamBlobs2 contrast sensitivity test is meant to be performed easily in the clinic or at home. The purpose of this study was to determine the intra-visit coefficient of repeatability of the CamBlobs2 compared with the near Pelli-Robson test, and the limits of agreement between these two tests on normally-sighted subjects. Methods Twenty-two normally-sighted subjects (mean age 28 ± 4 years) completed two trials of the near Pelli-Robson and CamBlobs2 contrast sensitivity tests within a single visit. Tests were performed monocularly on each eye in random order. Pelli-Robson tests were scored as 0.05 logCS for each letter read correctly after deducting the first triplet. CamBlob2 tests were scored as the highest line where two or fewer blobs were marked correctly. The coefficient of repeatability was determined as 1.96 times the standard deviation of the difference between the two measurements using the same type of chart on the same eye. The limits of agreement between the two tests were evaluated using Bland-Altman analysis. Results The mean difference between intra-visit measurements for both the near Pelli-Robson and CamBlobs2 was less than 0.05 logCS and the coefficient of repeatability was within ±0.20 log CS for both left and right eyes. The mean ± standard deviation differences between near Pelli-Robson and CamBlobs2 scores was −0.08 ± 0.08 (limits of agreement: −0.24 to 0.09) for right eyes and −0.05 ± 0.10 (limits of agreement: −0.23 to 0.14) logCS for left eyes based on average measurements. Conclusions The intra-visit repeatability of CamBlobs2 was consistent with the near Pelli-Robson contrast sensitivity test (±0.20 logCS). With a 0.05 correction, the CamBlobs2 scores showed excellent agreement with the near Pelli-Robson contrast sensitivity test.
Article
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The focusing response of the human eye - accommodation - exhibits errors known as lags and leads. Lags occur when the stimulus is near and the eye appears to focus farther than the stimulus. Leads occur with far stimuli where the eye appears to focus nearer than the stimulus. We used objective and subjective measures simultaneously to determine where the eye is best focused. The objective measures were made with a wavefront sensor and an autorefractor, both of which analyze light reflected from the retina. These measures exhibited typical accommodative errors, mostly lags. The subjective measure was visual acuity, which of course depends not only on the eye's optics but also on photoreception and neural processing of the retinal image. The subjective measure revealed much smaller errors. Acuity was maximized at or very close to the distance of the accommodative stimulus. Thus, accommodation is accurate in terms of maximizing visual performance.
Article
Purpose: To compare corneal higher-order aberrations (HOA) following ultrathin Descemet stripping automated endothelial keratoplasty (UT-DSAEK) and Descemet membrane endothelial keratoplasty (DMEK). Design: Patient and outcome-masked, randomized controlled clinical trial. Participants: Patients with damaged or diseased endothelium from Fuchs endothelial dystrophy or pseudophakic bullous keratopathy who were considered good candidates for DMEK or UT-DSAEK. Methods: Corneal anterior and posterior surface HOA were measured with Scheimpflug imaging before surgery and at 3, 6, and 12 months post-operatively. Zernike orders 3-8 were calculated at 4.0- and 6.0-mm-diameter optical zones (OZ). HOA after UT-DSAEK and DMEK were compared and correlation was performed between best spectacle-corrected visual acuity (BSCVA) and HOA at each time point. Main outcome measures: Higher-order aberrations of the anterior and posterior cornea, expressed as the root mean square deviation from a best fit sphere reference surface. Results: At 3, 6, and 12 months after surgery, the posterior corneal surface had significantly less coma (P≤0.003) and total HOA (P≤0.001) in DMEK compared to UT-DSAEK (4.0- and 6.0-mm OZ). Posterior trefoil (P≤0.034), secondary astigmatism (P≤0.042), and tetrafoil (P≤0.045) were lower in DMEK than UT-DSAEK at 3, 6, or 12 months (either 4.0- or 6.0-mm OZ). There were no significant differences in anterior surface HOA between DMEK and UT-DSAEK at any time point. Compared to baseline, total posterior HOA was significantly increased (P≤0.036) in UT-DSAEK at 3, 6, and 12 months, in contrast to DMEK where it was significantly decreased (P≤0.044) at 6 and 12 months (4.0- and/or 6.0-mm OZ). At 6 and 12 months, posterior corneal total HOA correlated moderately with BSCVA (ρ≤0.635, P≤0.001) (4.0- and 6.0-mm OZ). There were no moderate or strong correlations between anterior or combined corneal surface HOA at any time point after surgery. Conclusions: DMEK results in less posterior corneal HOA compared to UT-DSAEK. DMEK decreases and UT-DSAEK increases posterior corneal HOA compared to pre-surgical values. Total posterior corneal HOA correlates moderately with 6- and 12-month post-operative visual acuity and may partially account for the better visual acuity observed after DMEK.
Article
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Purpose To investigate which baseline factors are predictive for success in controlling myopia progression in a group of children wearing MiSight Contact Lens (CLs). Methods Myopic patients (n = 41) fitted with MiSight CLs and followed up two years were included in this study. Bivariate analysis, a logistic regression analysis (LG) and a decision tree (DT) approach were used to screen for the factors influencing the success of the treatment. To assess the response, axial length (AL) changes were considered as main variable. Patients were classified based on a specific range of change of axial length at the end of each year of treatment as “responders” (R) (AL change <0.11 mm/per year) and “non-responders” (NR) (AL change ≥0.11 mm/per year). Results Of a total of forty-one Caucasian patients treated with MiSight CLs, 21 and 16 were considered responders in the first and the second year of follow-up, respectively. LG analysis showed that the only factor associated with smaller axial length growth was more time spent outdoors (p = 0.0079) in the first year of treatment. The decision tree analysis showed that in the responding group spending more than 3 and 4 h outdoors per week was associated with the best response in the first year and in the second year of treatment respectively. Conclusions The LR and the DT approach of this pilot study identifies time spent outdoors as a main factor in controlling axial eye growth in children treated with MiSight CLs.
Article
Significance: Visual performance with wavefront-guided (WFG) contact lenses has only been reported immediately after manufacture without time for habituation, and comparison has only been made with clinically unrefined predicate conventional lenses. We present comparisons of habitual corrections, best conventional scleral lenses, and WFG scleral lenses after habituation to all corrections. Purpose: The purpose of this study was to compare, in a crossover design, optical and visual performance of eyes with corneal ectasias wearing dispensed best conventional scleral lens corrections and dispensed individualized WFG scleral lens corrections. Methods: Ten subjects (20 eyes) participated in a randomized crossover study where best conventional scleral lenses and WFG scleral lenses (customized through the fifth radial order) were worn for 8 weeks each. These corrections, as well as each subject's habitual correction and normative data for normal eyes, were compared using (1) residual higher-order aberrations (HORMS), (2) visual acuity (VA), (3) letter contrast sensitivity (CS), and (4) visual image quality (logarithm of the visual Strehl ratio, or logVSX). Correlations were performed between Pentacam biometric measures and gains provided by WFG lenses. Results: Mean HORMS was reduced by 48% from habitual to conventional and 43% from conventional to WFG. Mean logMAR VA improved from habitual (+0.12) to conventional (-0.03) and further with WFG (-0.09); six eyes gained greater than one line with WFG over conventional. Area under the CS curve improved by 26% from habitual to conventional and 14% from conventional to WFG. The percentage of the eyes achieving normal levels were as follows: HORMS, 40% for conventional and 85% for WFG; VA, 50% for conventional and 85% for WFG; and CS, 60% for conventional and 90% for WFG. logVSX improved by 16% from habitual to conventional and 25% further with WFG. Reduction in aberrations with WFG lenses best correlated with posterior cornea radius of curvature. Conclusions: Visual performance was superior to that reported with nonhabituated WFG lens wear. With WFG lenses, HORMS and logVSX significantly improved, allowing more eyes to reach normal levels of optical and visual performance compared with conventional lenses.
Article
Purpose: To compare the refractive, visual, and aberrometric results with a new extended depth-of-focus intraocular lens (EDOF IOL) based on alternating positive and negative spherical aberration in the central 3.0 mm optical zone and an aspheric monofocal IOL of the same platform. Setting: Ophthalmology, University Hospital of Verona, Italy. Design: Prospective case series. Methods: Cataract patients free from other ocular disease had bilateral implantation of the EDOF Mini Well IOL or the monofocal Mini IOL. Four to 6 weeks after second-eye surgery, the refraction, visual acuity, defocus curve, contrast sensitivity, and photic symptoms were assessed. Wavefront analysis was performed. The primary endpoint of was the amplitude of the dioptric interval for 0.1 logarithm of the minimum angle of resolution (logMAR) visual acuity. The secondary endpoint was an aberration comparison between the two IOLs. Results: The study comprised two groups of 25 patients each. The corrected distance visual acuity was better with the monofocal IOL by 0.02 logMAR (P = .03). The 0.1 logMAR dioptric interval was 2.0 diopters (D) for the EDOF IOL and 1.0 D for the monofocal IOL (P < .001). The mean CDVA at -2.0 defocus was 0.15 logMAR ± 0.08 (SD) and 0.52 ± 0.14 logMAR, respectively (P < .001). There was no difference in contrast sensitivity or photic symptoms. The optical aberrations at 4.0 mm and 6.0 mm aperture diameters were similar in the two groups. Conclusion: The EDOF IOL based on spherical aberration provided greater depth of focus than the aspheric monofocal IOL without increasing optical aberrations and with few photic symptoms.
Chapter
The understanding of the role of higher order aberrations of the visual system has explained multiple optical phenomena to the researchers and clinicians alike. Many disorders are better understood now due to application of wavefront optics in ophthalmology. In this chapter, we first summarize the current basic understanding of higher order aberrations and then review the literature on the differences in the normative data from various demographic populations in the higher order aberrations noted. A pooled analysis of the data suggested that in most of the demographic databases, at a 6-mm wavefront diameter, the adult human eye tends to have anywhere between 0.3 and 0.4 μm of higher order aberrations root mean square (HOARMS). However, there were variations noted in sub-analysis of the Zernike modes between different populations. The role of normative data for a given population is that of a guideline. It gives base information on which individual wavefront profile of an eye can be evaluated for the differences between normal and abnormal.
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Presbyopia, an age-related ocular disorder, is characterized by the loss in the accommodative abilities of the human ocular system and afflicts more than 1.8 billion people world-wide. Conventional methods of correcting presbyopia fragment the field of vision, inherently resulting in significant vision impairment. We demonstrate the development, assembly and evaluation of autofocusing eyeglasses for restoration of accommodation without vision field loss. The adaptive optics eyeglasses consist of two variable-focus piezoelectric liquid lenses, a time-of-flight range sensor and low-power, dual microprocessor control electronics housed within an ergonomic frame. Patient-specific accommodation deficiency models were utilized to demonstrate a high-fidelity accommodative correction. Each accommodation correction calculation was performed in ~67 ms requiring 4.86 mJ of energy. The optical resolution of the system was 10.5 cycles/degree, featuring a restorative accommodative range of 4.3 D. This system can run for up to 19 hours between charge cycles and weighs ~132 g, allowing comfortable restoration of accommodative function
Article
Significance: It is difficult to determine the most efficacious refractive correction for individuals with Down syndrome using routine clinical techniques. New objective methods that optimize spectacle corrections for this population may reduce limitations on daily living by improving visual quality. Purpose: This article describes the methods and baseline characteristics of study participants in a National Eye Institute-sponsored clinical trial to evaluate objectively derived spectacle corrections in adults with Down syndrome. Intersession repeatability of the primary outcome measure (distance visual acuity) is also reported. Methods: Adults with Down syndrome were enrolled into a nine-visit study to compare clinically derived spectacle corrections and two different objective spectacle corrections derived from wavefront aberration data. Spectacle corrections were randomized and dispensed for 2 months each. Distance visual acuity was measured with a Bailey-Lovie-style chart. Intersession repeatability of acuity was established by performing difference versus mean analysis from binocular acuity measures obtained through habitual corrections at visits 1 and 2. Results: Thirty adults (mean ± standard deviation age, 29 ± 10 years) with a large range of refractive errors were enrolled. Presenting visual acuity at visit 1 was reduced (right eye, 0.47 ± 0.20 logMAR; left eye, 0.42 ± 0.17 logMAR). The mean difference between visits 1 and 2 was 0.02 ± 0.06 logMAR, with a coefficient of repeatability (1.96 × within-subject standard deviation) of 0.12 logMAR. Conclusions: This study seeks to investigate new strategies to determine optical corrections that may reduce commonly observed visual deficits in individuals with Down syndrome. The good intersession repeatability of acuity found in this study (six letters) indicates that, despite the presence of reduced acuity, adults with Down syndrome performed the outcome measure for this clinical trial reliably.
Article
Purpose: To assess the influence of small-incision lenticule extraction (SMILE) for high myopia on the visual image quality assessed by the logarithm of the Visual Strehl Ratio (logVSX), and put this into a clinical context by pairwise comparing the logVSX of postoperative eyes with those of myopic controls wearing spectacles and/or contact lenses. Setting: University Hospital DESIGN:: Prospective & cross-sectional clinical study METHODS:: Patients with a myopic spherical equivalent of at least 6 diopters treated with SMILE aimed at emmetropia and correspondingly myopic controls corrected with spectacles and/or contact lenses were included. The logVSX calculation was divided into habitual logVSX based on the wavefront aberration measurement directly, and optimal logVSX calculated in a theoretical through-focus experiment to obtain the best-achievable logVSX. Results: 117 eyes of 61 patients and 64 eyes of 34 myopic controls were included. SMILE did not affect the habitual logVSX, but worsened the optimal logVSX (P<0.001). The postoperative habitual logVSX was significantly worse compared to contact lenses (P=0.002). The postoperative optimal logVSX was significantly worse compared to both spectacles (P<0.01) and contact lenses (P=0.003). There was no difference in habitual or optimal logVSX between spectacles and contact lenses. Conclusions: SMILE for high myopia does not affect the habitual logVSX but decreases the optimal logVSX slightly. The postoperative habitual logVSX is worse than for contact lenses but not spectacles, and the postoperative optimal logVSX is worse than for both contact lenses and spectacles. There is no difference in either habitual or optimal logVSX between spectacles and contact lenses.
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Purpose: Assessment of pupil diameter in various light conditions and the corresponding corneal spherical aberrations in a cohort of Indian eyes with bilateral senile cataracts and the possible use of this data in aberrometric customization of intraocular lenses (IOLs). Methods: In this prospective observational study done at a tertiary eye care centre in India, the selected patients were subjected to measurement of their pupil diameters in scotopic, mesopic, and photopic conditions as well as the corresponding corneal spherical aberrations, using the Sirius Topographer (Costruzione Strumenti Oftalmici, Florence, Italy). Shapiro-Wilk test, Independent t-test, ANOVA with Bonferroni correction on post-hoc testing were used for statistical analysis. Results: 104 eyes of 52 patients were enrolled for the study. The mean age was 53 ± 11.88 years. The mean scotopic, mesopic, and photopic pupil sizes were 4.37 mm (4.11-4.63 mm), 3.92 mm (3.71 mm-4.15 mm), and 3.37 mm (3.18-3.67 mm), respectively. There was a statistically significant difference (P = <0.001) in the mean corneal spherical aberration measured at the 6 mm zone (0.23 ± 0.02 microns) and at the 4 mm zone (0.06 ± 0.01 microns). Conclusion: The mean corneal spherical aberration corresponding to the average mesopic pupil size of our patient population was substantially lower than that of the scotopic pupil size and also less than the amount corrected by most of the negative aspheric IOLs. This perhaps indicates the need for customising IOLs based on the spherical aberrations of cornea at the zone corresponding to the mesopic pupil diameter for optimal residual total postoperative spherical aberrations.
Article
Significance: To achieve maximum visual benefit, wavefront-guided scleral lens corrections (WGCs) are aligned with the underlying wavefront error of each individual eye. This requirement adds complexity to the fitting process. With a view toward simplification in lens fitting, this study quantified the consequences of placing WGCs at two pre-defined locations. Purpose: This study aimed to quantify performance reduction accompanying the placement of the WGC at two locations: (1) the average decentered location (ADL; average decentration observed across individuals wearing scleral lenses) and (2) the geometric center (GC) of the lens. Methods: Deidentified residual aberration and lens translation data from 36 conventional scleral lens-wearing eyes with corneal ectasia were used to simulate WGC correction in silico. The WGCs were decentered from the eye-specific pupil position to both the ADL and GC locations. The impact of these misalignments was assessed in terms of change (from the aligned, eye-specific pupil position) in higher-order root mean square (HORMS) wavefront error, change in log of the visual Strehl ratio (logVSX), and predicted change in logMAR visual acuity (VA). Results: As expected, HORMS increased, logVSX decreased, and predicted VA was poorer at both ADL and GC compared with the aligned condition (P < .001). Thirty-four of 36 eyes had greater residual HORMS, and 33 of 36 eyes had worse logVSX values at the GC than at the ADL. In clinical terms, 19 of 36 eyes at the ADL and 35 of 36 eyes at the GC had a predicted loss in VA of three letters or greater. Conclusions: The placement of the WGC at either ADL or GC is predicted to lead to a noticeable reduction in VA for more than half of the eyes studied, suggesting the simplification of the fitting process is not worth the cost in performance.
Article
Clinical relevance: Diagnosis and monitoring of keratoconus is increasingly being conducted with the aid of imaging equipment such as corneal aberrometry. There is a need to also know the confidence with which ocular aberration measurements can be made. Background: To assess the repeatability of lower- and higher-order aberration measurements in patients with keratoconus using the irx3 wavefront aberrometer (Imagine Eyes, Orsay, France) and evaluate correlations with corneal curvature. Methods: The irx3 wavefront aberrometer was used to measure bilateral lower- and higher-order ocular aberrations on 33 participants with keratoconus. Three measurements were taken from each eye to determine the repeatability of lower-order aberrations (quantified as sphere and cylinder in dioptres) and higher-order aberration co-efficients (up to eighth order in micrometres), coma, trefoil and total higher-order aberration root mean square (in micrometres). Corneal curvature was measured using the Pentacam HR system (OCULUS, Wetzlar, Germany). Results: Repeat measurements for lower-order aberrations resulted in larger co-efficients of repeatability than higher-order aberrations. Similarly, larger co-efficients of repeatability between repeated measures across all Zernike co-efficients were observed in eyes with severe keratoconus (that is, corneal curvature > 52 D) compared to eyes with flatter corneas. The difference between repeated measures tended to be significant for the lower-order aberrations regardless of corneal curvature. The highest correlations with corneal curvature for right and left eyes respectively, were identified for total higher-order aberration root mean square (r = 0.92, p < 0.001 and r = 0.91, p < 0.001), followed closely by coma (r = -0.93, p < 0.001 and r = -0.86, p < 0.001) and the Z (3, -1) co-efficient (r = -0.92, p < 0.001 and r = -0.86, p < 0.001 for right and left eyes, respectively). Conclusions: Lower-order aberrations tended to be less repeatable, indicating that instrument variability must be considered when monitoring progression. Total higher-order aberration root mean square and third-order aberrations, in particular the vertical coma Z (3, -1) co-efficient, demonstrated a stronger correlation with corneal curvature than the lower-order aberrations.
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Combined probe beam deflection (PBD) and wavefront sensor (WFS) technique are used to investigate the thermal distribution of gold nanourchins (GNU) in physiological saline (PS) using a low-power continuous NIR diode laser. Three different samples were prepared for the experiment: (S1) 0.5 mg/mL GNU only, (S2) 0.5 mL PS and 0.3 mL GNU, and (S3) 0.5 mL PS and 0.1 mL GNU. The laser transmission initially increases linearly as S3 > S2 > S1, but reaches a plateau and remains constant. The probe beam response in an adjective statistics process exhibited a stochastic behaviour at different positions and constant power in x- and y-directions. The beam view profiles showed a non-uniform intensity distribution and the addition of PS dramatically caused a blue shift indicating its cooling effect, S1 (20) warmer > S1(10) medium > S2 (20) cooler. S1 (10), S1 (20), and S2 (20) correspond to the samples irradiated with the laser power (mW) shown in the bracket. The peak-to-valley (PV) and root-mean-square (RMS) values demonstrated a non-linear intensity distribution during the scanning process. The greater PV values in deeper positions may well due to agglomeration, hence the sedimentation process. The Zernike coefficients with high absolute values represent the aberrations that cause the greatest distortion of the wavefront and found in the order of S2(20) > S1(10) > S1(20). This is consistent with PV wavefront slope and spatial period aberration relation. The opto-thermal coefficients were obtained as S2 (− 7.86 × 10⁻⁴⁾ > S3: 0.5 mL PS and 0.1 ml GNU (− 6.3 × 10⁻⁴), respectively.
Article
Clinical relevance: That myopic defocus, even if restricted to the peripheral retina, inhibits eye growth in young monkey eyes has motivated the therapy of myopia control through multifocal contact lens wear in children. Background: To understand how eye-length regulating mechanisms are triggered by light requires knowledge of retinal light spread. That is largely lacking for the multifocal contact lenses used in the therapy because empirical methods identifying just the defocus in dioptres are inadequate. Methods: "Through-focus" diffraction computations in contact lens/eye models with typical normal eye parameters, including polychromatic light, the chromatic aberrations and an M-cone phototransduction layer, offer estimates of retinal image spread for a range of viewing distances. Results: Point- and edge-spread distributions of activation of phototransduction in the central retina show that the addition of multifocal zones produces some veiling for in-focus viewing and substantial improvement of image quality for near targets in the unaccommodated eye. These effects are much reduced in the retinal periphery. Conclusion: Whatever therapeutic value there is in prescribing multifocal contact lenses for myopia control, it is not particularly dependent on the precise configuration of the multifocal zones, nor can it be ascribed to changes in image quality specific to the retinal periphery; its origin is more likely less blur for near targets, reducing the stimulus to accommodation.
Thesis
Retinal laser photocoagulation is commonly used to treat Diabetic Macular Edema. However, it is impossible with current laser systems to prevent some degree of damage to healthy neighboring tissues, due to the lack of control of the 3D confinement and position of the laser impact. These limitations are mostly caused by ocular aberrations and the constant eye movement. Adaptive Optics (AO) is a technology used since 1997 which enables ocular aberrations compensation in real-time, providing images of the retina with an unbeaten resolution. Laser photocoagulation systems could benefit from the AO capacity to control the 3D confinement of the therapeutic laser and to generate high- resolution retinal images that could be used to guide the surgeon and to control the 3D position of the laser impact in the retina. However, a great effort still has to be made to meet laser photocoagulation requirements. This thesis consists of the design and realization of the first 3D high-resolution AO-assisted Laser Photocoagulation system. For this end, we first present a high spatiotemporal resolution characterization of the 3D PSF evolution within the eye, enabling the design of a high-performance AO system, adapted to a therapeutic application, i.e. 3D control of the laser confinement. Then, I used the high-resolution retinal imaging system ECURoeil to validate these results and develop new methods enabling the 4D exploration of the retina (volume + temporal evolution) in real-time, for 3D control of the laser impact position. Finally, all the developments have been brought together in the CLOVIS3D bench, a compact instrument to perform clinically the first therapeutic application of Adaptive Optics.
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The retinal image quality characterized by the modulation-transfer function of the eye was measured for two groups of subjects aged in the late twenties and mid sixties, respectively. In both groups, we obtained modulation transfer functions by using a double-pass method under the same experimental conditions: 4-mm artificial pupil, paralyzed accommodation, and objective control of the refractive state and centering. Results showed lower values of modulation in the retinal image for older subjects compared with the younger subjects. The modulation transfer function ratio is similar to that previously found for contrast-sensitivity measurements with subjects in the same age groups. These results suggest that a significant fraction of the loss in spatial vision with age has an optical origin. Apart from the well-known increase in intraocular scattering, there also appears to be an increment in ocular aberration that causes an additional reduction in the contrast of retinal images.
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To determine the average optical performance of the human eye, in terms of the modulation transfer function (MTF), as a function of age. An apparatus was constructed to measure the ocular MTF, based on the recording of images of a green, 543-nm laser-point source after reflection in the retina and double pass through the ocular media. MTFs were computed from the average of three 4-second-exposure double-pass images recorded by a slow-scan, cooled charge-coupled device camera. The ocular MTF was measured for three artificial pupil diameters (3 mm, 4 mm, and 6 mm) with paralyzed accommodation under the best refractive correction in 20 subjects for each of three age categories: young subjects aged 20 to 30 years, middle-aged subjects aged 40 to 50 years, and older subjects aged 60 to 70 years. The selected subjects passed an ophthalmologic examination, excluding subjects with any form of ocular or retinal disease, spherical or cylindrical refractive errors exceeding 2 D, and corrected visual acuity lower than 1 (0.8 in the older age group). The average MTF was determined for each age group and pupil diameter. A two-parameter analytical expression was proposed to represent the average MTF in each age group for every pupil diameter. The ocular MTFs declined as age increased from young to older groups. The SD of the MTF results within age groups was lower than the differences between the mean for each group. The average optical performance of the human eye progressively declines with age. These MTF results can serve as a reference for determining mean ocular optics according to age.
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From both a fundamental and a clinical point of view, it is necessary to know the distribution of the eye's aberrations in the normal population and to be able to describe them as efficiently as possible. We used a modified Hartmann-Shack wave-front sensor to measure the monochromatic wave aberration of both eyes for 109 normal human subjects across a 5.7-mm pupil. We analyzed the distribution of the eye's aberrations in the population and found that most Zernike modes are relatively uncorrelated with each other across the population. A principal components analysis was applied to our wave-aberration measurements with the resulting principal components providing only a slightly more compact description of the population data than Zernike modes. This indicates that Zernike modes are efficient basis functions for describing the eye's wave aberration. Even though there appears to be a random variation in the eye's aberrations from subject to subject, many aberrations in the left eye were found to be significantly correlated with their counterparts in the right eye.
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We studied the age dependence of the relative contributions of the aberrations of the cornea and the internal ocular surfaces to the total aberrations of the eye. We measured the wave-front aberration of the eye with a Hartmann-Shack sensor and the aberrations of the anterior corneal surface from the elevation data provided by a corneal topography system. The aberrations of the internal surfaces were obtained by direct subtraction of the ocular and corneal wave-front data. Measurements were obtained for normal healthy subjects with ages ranging from 20 to 70 years. The magnitude of the RMS wave-front aberration (excluding defocus and astigmatism) of the eye increases more than threefold within the age range considered. However, the aberrations of the anterior corneal surface increase only slightly with age. In most of the younger subjects, total ocular aberrations are lower than corneal aberrations, while in the older subjects the reverse condition occurs. Astigmatism, coma, and spherical aberration of the cornea are larger than in the complete eye in younger subjects, whereas the contrary is true for the older subjects. The internal ocular surfaces compensate, at least in part, for the aberrations associated with the cornea in most younger subjects, but this compensation is not present in the older subjects. These results suggest that the degradation of the ocular optics with age can be explained largely by the loss of the balance between the aberrations of the corneal and the internal surfaces.
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The standard Zernike polynomial functions are reformulated in a way so that the number of functions (or terms) needed to describe an arbitrary wavefront surface to a given Zernike radial order is reduced by a factor of approximately two, and the terms are described in a fashion quite similar to that used to describe common sphero-cylindrical errors of the eye. A wavefront is represented using these terms by assigning a pair of values, a magnitude and an axis, to all terms that are radially symmetric so that the individual aberrations are presented in a way similar to the way common astigmatism is currently given in terms of cylinder power and axis. The root mean square of these magnitudes gives the root mean square wavefront error just as does the root mean square of the standard Zernike coefficients. Formulas are given to convert standard Zernike coefficients to the magnitude and axis values.
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A matrix method is developed that allows a new set of Zernike coefficients that describe a surface or wave front appropriate for a new aperture size to be found from an original set of Zernike coefficients that describe the same surface or wave front but use a different aperture size. The new set of coefficients, arranged as elements of a vector, is formed by multiplying the original set of coefficients, also arranged as elements of a vector, by a conversion matrix formed from powers of the ratio of the new to the original aperture and elements of a matrix that forms the weighting coefficients of the radial Zernike polynomial functions. In developing the method, a new matrix method for expressing Zernike polynomial functions is introduced and used. An algorithm is given for creating the conversion matrix along with computer code to implement the algorithm.
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To describe monochromatic optical aberrations of the eye as a function of age. One hundred fourteen subjects with a spherical equivalent within +/-3.50 D from emmetropia, corrected visual acuity of 20/40 or better, and normal findings in an ophthalmic examination were enrolled. The mean age was 43.2 +/- 24.5 years (range, 5.7-82.3). Monochromatic optical aberrations were measured with a Hartmann-Shack wavefront sensor after pharmacological dilation and cycloplegia. For a 5-mm pupil and for third- to seventh-, third-, fourth-, and fifth- to seventh-order aberrations, as well as for coma and spherical aberrations, the root mean square (RMS) error as a function of age was modeled by a second-order polynomial regression. It decreased progressively through childhood, adolescence, and early adulthood; reached a minimum level during the fourth decade of life, then increased progressively with age, to age 82. For a 5-mm pupil, the mean modulation transfer function (MTF) was reduced in both the child-teenage (5-20 years; n = 29) and the elderly (61-82 years; n = 37) groups versus the middle-aged adult group (41-60 years; n = 24; P < 0.05). In young adults (21-40 years; n = 23) and elderly subjects, the MTF curves were very close and almost superimposed at spatial frequencies higher than 38 cyc/deg. Aberrations of the whole eye were objectively measured from early childhood to an advanced age, and the relationship between monochromatic aberrations and age has been shown to fit a quadratic model. The results suggest that the definition of emmetropization should be broadened to include the reduction of higher order aberrations.
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Recently, instruments for the measurement of wavefront aberration in the living human eye have been widely available for clinical applications. Despite the extensive background experience on wavefront sensing for research purposes, the information derived from such instrumentation in a clinical setting should not be considered a priori precise. We report on the variability of such an instrument at two different pupil sizes. A clinical aberrometer (COAS Wavefront Scienses, Ltd) based on the Shack-Hartmann principle was employed in this study. Fifty consecutive measurements were performed on each right eye of four subjects. We compared the variance of individual Zernike expansion coefficients as determined by the aberrometer with the variance of coefficients calculated using a mathematical method for scaling the expansion coefficients to reconstruct wavefront aberration for a reduced-size pupil. Wavefront aberration exhibits a marked variance of the order of 0.45 microns near the edge of the pupil whereas the central part appears to be measured more consistently. Dispersion of Zernike expansion coefficients was lower when calculated by the scaling method for a pupil diameter of 3 mm as compared to the one introduced when only the central 3 mm of the Shack - Hartmann image was evaluated. Signal-to-noise ratio was lower for higher order aberrations than for low order coefficients corresponding to the sphero-cylindrical error. For each subject a number of Zernike expansion coefficients was below noise level and should not be considered trustworthy. Wavefront aberration data used in clinical care should not be extracted from a single measurement, which represents only a static snapshot of a dynamically changing aberration pattern. This observation must be taken into account in order to prevent ambiguous conclusions in clinical practice and especially in refractive surgery.
Article
We explain the nature of optical aberrations and how they may be represented mathematically. We describe the use of Zernike polynomials in a way that will aid understanding and provide potential tools for manipulating the wavefront aberration expressions given in this form.
Article
Purpose: To test the accuracy, tolerance and repeatability of the COAS aberrometer (Wavefront Sciences, Inc.) with model eyes and normal human eyes. Methods: Model eyes were constructed from six PMMA, single-surface lenses with known characteristics. Accuracy was evaluated by comparing theoretical predictions with measured spherical aberration, coma, defocus, and astigmatism. Tolerance to axial and lateral misalignment was measured by controlled displacements of the model eye relative to the aberrometer. Repeatability was tested with measurements taken within seconds or across several days on the same model eye. The same tolerance and repeatability experiments were then repeated on human eyes. Results: Accuracy of spherical aberration and coma agreed closely with theoretical predictions (e.g. for all six aspheric models, the mean difference between predicted and measured Z4\0 was 0.006 microns). Defocus and astigmatism were accurately measured (e.g. measured defocus was within +/- 0.25 diopters over a +/-3 D range of refractive error). Axial displacements over the range +/- 2.5 cm had little effect on measurements for myopic and emmetropic model eyes. Also, lateral displacements over the range +/-1.5 mm did not produce significant coma. The standard deviations of repeated measurements of higher order RMS were less than 1% of the mean over seconds and less than 8% over days for model eyes. Tolerance to small lateral displacements was also observed for human eyes. Rotational (fixation) errors over a 3° range increased measurement variability, but not enough to fully account for long-term variations in human eyes. Conclusion: The COAS aberrometer can measure 2nd, 3rd, and 4th order aberrations accurately and repeatably on model eyes. Variability in human eye measurements is mostly due to fixational error and other physiological factors, rather than instrument fluctuations or errors of alignment.
Article
Orthogonal polynomials are routinely used to represent complex surfaces over a specified domain. In optics, Zernike polynomials have found wide application in optical testing, wavefront sensing, and aberration theory. This set is orthogonal over the continuous unit circle matching the typical shape of optical components and pupils. A variety of techniques has been developed to scale Zernike expansion coefficients to concentric circular subregions to mimic, for example, stopping down the aperture size of an optical system. Here, similar techniques are used to rescale the expansion coefficients to new pupil sizes for a related orthogonal set: the pseudo-Zernike polynomials.
Article
New measurements of the chromatic difference of focus of the human eye were obtained with a two-color, vernier-alignment technique. The results were used to redefine the variation of refractive index of the reduced eye over the visible spectrum. The reduced eye was further modified by changing the refracting surface to an aspherical shape to reduce the amount of spherical aberration. The resulting chromatic-eye model provides an improved account of both the longitudinal and transverse forms of ocular chromatic aberration.
Article
The Shack-Hartmann wave-front sensor offers many theoretical advantages over other methods for measuring aberrations of the eye; therefore it is essential that its accuracy be thoroughly tested. We assessed the accuracy of a Shack-Hartmann sensor by directly comparing its measured wave-front aberration function with that obtained by the Smirnov psychophysical method for the same eyes. Wave-front profiles measured by the two methods agreed closely in terms of shape and magnitude with rms differences of approximately lambda/2 and approximately lambda/6 (5.6-mm pupil) for two eyes. Primary spherical aberration was dominant in these profiles, and, in one subject, secondary coma was opposite in sign to primary coma, thereby canceling its effect. Discovery of an unusual, subtle wave-front anomaly in one individual further demonstrated the accuracy and sensitivity of the Shack-Hartmann wave-front sensor for measuring the optical quality of the human eye.
Article
We measured the contrast sensitivity (CS) of a group of older subjects through natural pupils and compared the results with those from a group of younger subjects. We also measured each subject's monochromatic ocular wave-front aberrations using a crossed-cylinder aberroscope and calculated their modulation transfer functions (MTF's) and root-mean-squared (RMS) wave-front aberrations for fixed pupil diameters of 4 mm and 6 mm and for a natural pupil diameter. The CS at a natural pupil diameter and the MTF computed for a fixed pupil diameter were found to be significantly poorer for the older group than for the younger group. However, the older group showed very similar MTF's and significantly smaller RMS wave-front aberrations compared with the younger group at their natural pupil diameters, owing to the effects of age-related miosis. These results suggest that although monochromatic ocular wave-front aberrations for a given pupil size increase with age, the reduction in CS with age is not due to this increase.
Article
To compare quantitatively three techniques to measure the optical aberrations of the human eye: laser ray tracing (LRT), the Hartmann-Shack wavefront sensor (H-S), and the spatially resolved refractometer (SRR). LRT and H-S are objective imaging techniques, whereas SRR is psychophysical. Wave aberrations were measured in two normal subjects with all three techniques implemented in two different laboratories. We compared the experimental variability of the results obtained with each technique with the overall variability across the three methods. For the two subjects measured (RMS wavefront error 0.5 microm and 0.9 microm, respectively), we found a close agreement; the average standard deviation of the Zernike coefficients within a given method was 0.07 microm, whereas the average global standard deviation across techniques was 0.09 microm, which is only slightly higher. There is a close match between the Zernike coefficients obtained by LRT, H-S, and SRR. Thus, all three techniques provide similar information concerning wave aberration when applied to normal human eyes. However, the methods are operationally different, and each has advantages and disadvantages depending on the particular application.
Article
To investigate the relations between age and the optical aberrations of the whole eye. The eye's optical quality, as measured by the modulation transfer function (MTF), degrades with age, but the MTF does not provide a means to assess the contributions of individual aberrations, such as coma, spherical aberration, and other higher order aberrations to changes in optical quality. The method used in this study provides measures of individual aberrations and overall optical quality. Wave aberrations in 38 subjects were measured psychophysically using a spatially resolved refractometer. Data were fit with Zernike polynomials up to the seventh order to provide estimates of 35 individual aberration terms. MTFs and root mean square (RMS) wavefront errors were calculated. Subjects ranged in age from 22.9 to 64.5 years, with spherical equivalent corrections ranging from +0.5 to -6.0 D. Overall RMS wavefront error (excluding tilts, astigmatism, and defocus) was significantly positively correlated with age (r = 0.33, P = 0.042). RMS error for the highest order aberrations measured (fifth through seventh order) showed a strong positive correlation with age (r = 0.57, P = 0.0002). Image quality, as quantified by the MTF, also degraded with age. Wave aberrations of the eye increase with age. This increase is consistent with the loss of contrast sensitivity with age observed by other investigators.
Article
Wavefront aberrations were measured using a psychophysical ray-tracing technique in both eyes of 316 emmetropic and moderately myopic school children and young adults. Myopic subjects were found to have greater mean root mean square (RMS) value of wavefront aberrations than emmetropic subjects. Emmetropic adults had the smallest mean RMS, which remained smaller than the values for myopic adults and children and for emmetropic children both when second order Zernike aberrations (astigmatism) and third order Zernike aberrations were removed. Twenty percent of myopic adults had RMS values greater than values for all of the emmetropic adults, with significantly greater values for Zernike aberrations from second to seventh orders. High amounts of wavefront aberrations, which degrade the retinal image, may play a role in the development of myopia.
Article
Monochromatic ocular aberrations in 108 eyes of a normal young population (n=59) were studied. The wave-front aberration were obtained under natural conditions using a near-infrared Shack-Hartmann wave-front sensor. For this population and a 5 mm pupil, more than 99% of the root-mean square wave-front error is contained in the first four orders of a Zernike expansion and about 91% corresponds only to the second order. Comparison of wave-fronts aberrations from right and left eye in 35 subjects, showed a good correlation between most of the second- and third-order terms and a slight (but not clear) tendency for mirror symmetry between eyes.
Article
A statistical model of the wavefront aberration function of the normal, well-corrected eye was constructed based on normative data from 200 eyes which show that, apart from spherical aberration, the higher-order aberrations of the human eye tend to be randomly distributed about a mean value of zero. The vector of Zernike aberration coefficients describing the aberration function for any individual eye was modelled as a multivariate, Gaussian, random variable with known mean, variance and covariance. The model was verified by analysing the statistical properties of 1000 virtual eyes generated by the model. Potential applications of the model include computer simulation of individual variation in aberration structure, retinal image quality, visual performance, benefit of novel designs of ophthalmic lenses, or outcome of refractive surgery.
Article
Recent developments in technologies to correct aberrations in the eye have fostered extensive research in wave-front sensing of the eye, resulting in many reports of Zernike expansions of wave-front errors of the eye. For different reports of Zernike expansions, to be compared, the same pupil diameter is required. Since no standard pupil size has been established for reporting these results, a technique for converting Zernike expansion coefficients from one pupil size to another is needed. This investigation derives relationships between the Zernike expansion coefficients for two different pupil sizes.
Article
A Shack-Hartmann aberrometer was used to measure the monochromatic aberration structure along the primary line of sight of 200 cyclopleged, normal, healthy eyes from 100 individuals. Sphero-cylindrical refractive errors were corrected with ophthalmic spectacle lenses based on the results of a subjective refraction performed immediately prior to experimentation. Zernike expansions of the experimental wave-front aberration functions were used to determine aberration coefficients for a series of pupil diameters. The residual Zernike coefficients for defocus were not zero but varied systematically with pupil diameter and with the Zernike coefficient for spherical aberration in a way that maximizes visual acuity. We infer from these results that subjective best focus occurs when the area of the central, aberration-free region of the pupil is maximized. We found that the population averages of Zernike coefficients were nearly zero for all of the higher-order modes except spherical aberration. This result indicates that a hypothetical average eye representing the central tendency of the population is nearly free of aberrations, suggesting the possible influence of an emmetropization process or evolutionary pressure. However, for any individual eye the aberration coefficients were rarely zero for any Zernike mode. To first approximation, wave-front error fell exponentially with Zernike order and increased linearly with pupil area. On average, the total wave-front variance produced by higher-order aberrations was less than the wave-front variance of residual defocus and astigmatism. For example, the average amount of higher-order aberrations present for a 7.5-mm pupil was equivalent to the wave-front error produced by less than 1/4 diopter (D) of defocus. The largest pupil for which an eye may be considered diffraction-limited was 1.22 mm on average. Correlation of aberrations from the left and right eyes indicated the presence of significant bilateral symmetry. No evidence was found of a universal anatomical feature responsible for third-order optical aberrations. Using the Marechal criterion, we conclude that correction of the 12 largest principal components, or 14 largest Zernike modes, would be required to achieve diffraction-limited performance on average for a 6-mm pupil. Different methods of computing population averages provided upper and lower limits to the mean optical transfer function and mean point-spread function for our population of eyes.
Article
To evaluate the Complete Ophthalmic Analysis System (COAS; WaveFront Science) for accuracy, repeatability, and instrument myopia when measuring myopic refractive errors. We measured the refractive errors of 20 myopic subjects (+0.25 to -10 D sphere; 0 to -1.75 D cylinder) with a COAS, a phoropter, and a Nidek ARK-2000 autorefractor. Measurements were made for right and left eyes, with and without cycloplegia, and data were analyzed for large and small pupils. We used the phoropter refraction as our estimate of the true refractive error, so accuracy was defined as the difference between phoropter refraction and that of the COAS and autorefractor. Differences and means were computed using power vectors, and accuracy was summarized in terms of mean vector and mean spherocylindrical power errors. To assess repeatability, we computed the mean vector deviation for each of five measurements from the mean power vector and computed a coefficient of repeatability. Instrument myopia was defined as the difference between cycloplegic and noncycloplegic refractions for the same eyes. Without cycloplegia, both the COAS and autorefractor had mean power vector errors of 0.3 to 0.4 D. Cycloplegia improved autorefractor accuracy by 0.1 D, but COAS accuracy remained the same. For large pupils, COAS accuracy was best when Zernike mode Z4(0) (primary spherical aberration) was included in the computation of sphere power. COAS repeatability was slightly better than autorefraction repeatability. Mean instrument myopia for the COAS was not significantly different from zero. When measuring myopes, COAS accuracy, repeatability, and instrument myopia were similar to those of the autorefractor. Error margins for both were better than the accuracy of subjective refraction. We conclude that in addition to its capability to measure higher-order aberrations, the COAS can be used as a reliable, accurate autorefractor.
Article
To validate the accuracy, tolerance, and repeatability of the complete ophthalmic analysis system aberrometer (COAS, Wavefront Sciences Inc.) with model eyes and normal human eyes. Model eyes were constructed from six polymethyl methacrylate, single-surface lenses with known characteristics. Accuracy of second-order aberrations was verified by measuring defocus and astigmatism induced by series of spherical and cylindrical trial lenses. Accuracy of higher-order aberrations was evaluated by comparing ray-tracing predictions with measured spherical aberration and coma of the aspheric model eyes. Tolerance to axial and lateral misalignment was measured by controlled displacements of the model eye relative to the aberrometer. Repeatability was tested on the same model eyes with repeated measurements taken within 1 s or within half an hour with realignment between each trial. Analyses were based on a 5-mm pupil diameter. Defocus and astigmatism were accurately measured within the working range of the instrument automatic focus adjustment (e.g., measured defocus was within +/-0.25 diopters over a -6.50 to +3.00 D range of refractive error). Accuracy of spherical aberration and coma agreed closely with theoretical predictions (e.g., for all six aspheric models, the mean absolute difference between predicted and measured Z(4)0 was 0.007 microm). Axial displacements over the range +/-2.5 mm had little effect on measurements for myopic and emmetropic model eyes. Also, lateral displacements over the range +/-1.5 mm did not produce significant coma. The standard deviations of repeated measurements of higher-order root mean square on model eyes were <1% of the mean with repeated measures within 1 s and 10% of the mean for five individual measurements with realignment in between each. Tolerance to small lateral displacements was also observed for human eyes. The complete ophthalmic analysis system aberrometer can measure second-, third-, and fourth-order aberrations accurately and repeatedly on model eyes.
Article
To explore the distribution of ocular higher-order aberrations (HOAs, 3rd to 6th orders) in the population, evaluate the symmetry of ocular aberrations between right and left eyes in each subject using a Hartmann-Shack wavefront sensor, and study the differences in aberration as a function of age. Cullen Eye Institute, Baylor College of Medicine, Houston, Texas, USA. Ocular HOAs were examined across a 6.0 mm pupil in 532 eyes of 306 subjects (mean age 41 years +/- 10 [SD] [range 20 to 71 years]; mean WaveScan spherical equivalent -3.39 +/- 2.84 diopters [D] [range -11.56 to 7.60 D]) using the WaveScan system (Visx, Inc.). Zernike coefficients and root-mean-square (RMS) values of HOAs, spherical aberration (SA, Z(4)(0) and Z(6)(0)), and coma (Z(3)(-1), Z(3)(1), Z(5)(-1), and Z(5)(1)) were analyzed. Correlation analysis was performed to assess the association between ocular HOAs and age and investigate the aberration symmetry between right and left eyes. For individual terms, the highest mean absolute values were for 4th-order SA (Z(4)(0)), 3rd-order coma, and trefoil terms. The mean RMS values of HOA, SA, and coma were 0.305 +/- 0.095 microm, 0.128 +/- 0.074 microm, and 0.170 +/- 0.089 microm, respectively. Moderate to high correlations were found between the right and left eyes for HOA, SA, and coma (Pearson correlation coefficient = 0.601, 0.776, and 0.511, respectively; all P<.001). Thirteen of the 22 Zernike terms (59%) were significantly correlated across eyes (Bonferroni correction, P'<.05/22). Higher-order aberrations, SA, and coma were weakly correlated with age (r = 0.317, 0.273, and 0.176, respectively; all P<.002). Wavefront aberrations varied widely among subjects and increased slightly with age. A moderate to high degree of mirror symmetry existed between right and left eyes.
Article
Wave aberrations were measured with a Shack-Hartmann wavefront sensor (SHWS) in the right eye of a large young adult population when accommodative demands of 0, 3, and 6 D were presented to the tested eye through a Badal system. Three SHWS images were recorded at each accommodative demand and wave aberrations were computed over a 5-mm pupil (through 6th order Zernike polynomials). The accommodative response was calculated from the Zernike defocus over the central 3-mm diameter zone. Among all individual Zernike terms, spherical aberration showed the greatest change with accommodation. The change of spherical aberration was always negative, and was proportional to the change in accommodative response. Coma and astigmatism also changed with accommodation, but the direction of the change was variable. Despite the large inter-subject variability, the population average of the root mean square for all aberrations (excluding defocus) remained constant for accommodative levels up to 3.0 D. Even though aberrations change with accommodation, the magnitude of the aberration change remains less than the magnitude of the uncorrected aberrations, even at high accommodative levels. Therefore, a typical eye will benefit over the entire accommodative range (0-6 D) if aberrations are corrected for distance viewing.
Article
To investigate age-related changes in ocular and corneal higher-order wavefront aberrations and elucidate relative contributions of the cornea and the lens in the age-related changes. Observational case series. Corneal and ocular higher-order wavefront aberrations in the central 6 mm diameter were measured with videokeratography and the Hartmann-Shack wavefront aberrometer in 75 normal eyes of 75 patients with a mean age of 43.5 +/- 11.7 years (range, 18-69 years). Higher-order wavefront aberrations were calculated with Zernike polynomials up to sixth order. From the Zernike coefficients, we calculated root mean square (RMS) of coma and spherical aberration. To examine age-related changes of the polarity of spherical aberration, the changes of the Zernike coefficient Z(4)(0) was also investigated. Both corneal (r =.307, P =.007) and ocular (r =.334, P =.0033) coma RMS showed positive correlations with age. There was a positive correlation between corneal and ocular coma RMS (r =.468, P <.0001). The RMS of corneal spherical aberration did not change with aging (r =.153, P =.1895), whereas the RMS of ocular spherical aberration had a positive correlation with aging (r =.308, P =.0068). These results suggest that the ocular coma increases with age, mainly because of the increase in the corneal coma, and the ocular spherical aberration increases with age, mainly because of the increase in the spherical aberration in the internal optics.
Article
To compare the accuracy and verify the reliability of different commercial and experimental prototypes of aberrometers using a small group of normal subjects with low myopia. Three different devices were used to measure the wavefront aberration of five normal myopic eyes: 1) Zywave--commercial aberrometer based on a Hartmann-Shack wavefront sensor; 2) Tracey--commercial system based on the laser ray tracing principle; and 3) an experimental laboratory laser ray tracing instrument working at two different wavelengths (532 and 786 nm). A series of five measurements were taken for each subject. Pupil diameter and alignment were controlled. All wave aberration maps were reduced to a common 6.5-mm pupil diameter, and then the mean and standard deviation were computed for the series, as well as the global average and standard deviation for each subject. Despite several important differences among devices and sessions, the results obtained with the different devices were equivalent. The main difference found between aberrometers was due to the longitudinal chromatic aberration caused by the use of different wavelengths. The signal-to-noise ratio estimated from the raw data was moderate, 12, but could be improved by a factor of 2 by discarding those measurements with a higher deviation from the mean and averaging the remaining data, which was the approach implemented in the Zywave instrument. The aberrometers tested were reliable in normal eyes with low myopia. Aberrometry is a robust but noisy technique. Accuracy is limited by noise and other sources of variability, including the size and alignment of the pupil. These conclusions might not apply to eyes with large aberrations.
Article
To quantify ocular higher-order aberrations (HOAs) in eyes with supernormal vision, that is, natural uncorrected visual acuity (UCVA) > or = 20/15, to analyze the correlation between ocular HOAs and age in these eyes, and to investigate the correlation of HOAs between right and left eyes. Observational case series. Ocular HOAs were examined across a naturally dilated pupil with a diameter > or = 6.0 mm in 70 eyes of 35 subjects with > or = 20/15 UCVA (mean age 24.3 years +/- 7.7 [SD]) using the Nidek OPD scan wavefront aberrometer. Root-mean-square (RMS) values of HOA, total spherical aberration (TSA), total coma (TC), and total trefoil (TT) were analyzed. Correlation analysis was performed to assess the association between ocular HOAs and age and the correlation of HOAs between right and left eyes. Mean RMS values were 0.334 +/- 0.192 microm for HOA, 0.110 +/- 0.077 microm for TSA, 0.136 +/- 0.081 microm for TC, and 0.268 +/- 0.220 microm for TT. There were no significant differences in the mean values of HOA, TSA, TC, and TT between right and left eyes. The Pearson correlation coefficient between right and left eyes for TSA was 0.764 (P<.0001). No significant correlation was found between right and left eyes for HOA, TC, and TT. No significant correlation was found between each of the ocular aberrations and age. The amount of ocular HOAs in eyes with natural supernormal vision is not negligible, and is comparable to the reported amount of HOAs in myopic eyes.
Article
To study the distribution of ocular higher-order aberrations (HOAs) in a myopic population and to assess the repeatability of HOA measurements determined by a commercially available skiascopic wavefront sensor. Department of Ophthalmology, Assaf Harofeh Medical Center, Zerifin, Israel. Ocular HOAs were examined 3 times across a 6.0 mm naturally dilated pupil in 61 eyes using the Optical Path Difference (OPD)-scan wavefront aberrometer. Root-mean-square (RMS) values of HOAs, total spherical aberration (TSA), total coma (TC), and total trefoil (TT) were analyzed. Correlation analysis was performed to assess the aberration symmetry between right and left eyes. The repeatability of the OPD-scan measurements was assessed by calculating Pearson r correlation coefficients between each pair of measurements and the interclass correlation coefficients between the 3 measurements of each score. The mean RMS values of HOAs, TSA, TC, and TT were 0.347 microm +/- 0.252 (SD), 0.120 +/- 0.174 microm, 0.165 +/- 0.168 microm, and 0.252 +/- 0.157 microm, respectively. The HOAs, TSA, TC, and TT changed slightly and not significantly with increasing refractive error (all P>.05). The RMS level of HOAs and TTR of the 3rd measurement was significantly different from the 1st and 2nd measurements (P<.05), with overall low correlation between the 3 measurements for the HOAs, TSA, TC, and TT. The ocular wavefront aberrations varied greatly from subject to subject. Ocular HOAs were not correlated with refractive error. The repeatability of HOAs measurements with the OPD-aberrometry was low.
Article
To quantify the higher order aberrations of refractive surgery candidates and compare the wavefront-determined refractions with manifest refractions refined with a +/- 0.25 Jackson cross cylinder. Results of 226 consecutive patients (418 eyes) were analyzed with the WaveScan WavePrint system (VISX, Santa Clara, Calif). Only patients with normal eyes without previous surgery were included. The mean spherical equivalent refraction determined with wavefront analysis was -3.40 +/- 3.14 diopters (D) (range: -10.72 to +5.41 D). The largest amount of higher order aberrations was detected with : a 6-mm pupil diameter (coma 0.14 +/- 0.08 microm; trefoil 0.10 +/- 0.07 microm; spherical aberrations 0.09 +/- 0.07 microm). The mean root-mean-square of higher order aberrations and total aberrations were 0.23 +/- 0.11 microm and 4.00 +/- 2.45 microm, respectively. No statistically significant correlation was noted between higher order aberrations and gender (P = 0.7) or between higher order aberration and refractive level (P > .59). The mean differences in spherical equivalent refraction, sphere, and cylinder between WaveScan measurements and manifest refraction were 0.36 +/- 0.41 D, 0.40 +/- 0.44 D, and 0.28 +/- 0.32 D, respectively. This study provides reference values for higher order aberrations in normal refractive surgery candidates. Wavefront analysis also proved to be a valuable tool for objectively measuring preoperative refractive error.
Article
To analyze the distribution of human higher-order wavefront aberrations (3rd- to 6th-order) from the internal optics (WA(internal)) and the variations with age and to evaluate the degree of compensation that the internal optics provide for anterior corneal aberrations (WA(cornea)). Cullen Eye Institute, Baylor College of Medicine, Houston, Texas, USA. With assumption of a simple model for the eye, the WA(internal) were obtained by direct subtraction of the WA(cornea) from the ocular aberrations (WA(eye)). The WA(eye) were measured using the WaveScan system (Visx, Inc.), and the WA(cornea) were computed from the topographic data (Humphrey Atlas) using the CTView program (Sarver and Associates, Inc.). In 144 eyes of 114 normal patients (age 20 to 69 years), WA(internal) were calculated for a 6.0 mm pupil and a compensation factor (CF) was computed, with positive values representing compensation of WA(cornea) by WA(internal) and negative values indicating that the internal surfaces add aberrations to those of the cornea. There was wide individual variation in WA(internal). The mean coefficient for 4th-order spherical aberration (Z(4)(0)) was -0.145 microm +/-0.094 (SD) (95% confidence interval [CI], -0.160 to -0.130 microm); 95.1% of eyes had negative values. The mean root-mean-square value for HOAs was 0.334 +/- 0.096 microm (95% CI, 0.319 to 0.350 microm). Moderate to high correlations were found between the right and left eyes in HOAs, 4th-order and 6th-order spherical aberration coefficients (Z(4)(0) and Z(6)(0)). With increasing age, the HOAs did not change, whereas the negative coefficients for Z(4)(0) tended to become less negative. Only the term Z(4)(0) had a CF significantly correlated with increasing age (r=-0.338, P<.05 with Bonferroni correction). WA(internal) varied widely among patients, and a moderate to high degree of mirror symmetry existed between the right and left eyes. Internal surfaces compensated at least partially for the HOA and Z(4)(0) in most eyes, and this compensation decreased only mildly with increasing age.
Article
Refractive surgery has stimulated the development of aberrometers, which are instruments that measure higher-order aberrations. The purpose of this study was to test one clinical aberrometer, the Complete Ophthalmic Analysis System (COAS), for its accuracy, repeatability, and instrument myopia for measuring sphere and astigmatism and its repeatability for measuring higher-order aberrations. Aberrations of 56 normal eyes (28 subjects) were measured with and without cycloplegia using a COAS, a conventional autorefractor and by subjective refraction. We evaluated lower-order accuracy (sphere and astigmatism) of the COAS and autorefractor by comparing that data with that of subjective refraction. We also tested COAS lower- and higher-order repeatability for 5 measurements taken in less than 1 minute. We evaluated instrument myopia by comparing cycloplegic and noncycloplegic measurements of the same eye. Data were analyzed for a 5.0-mm-diameter pupil. Mean COAS spherical error was between -0.1 and +0.4 diopters (D), depending on cycloplegia and the kind of sphere power computation selected. Cylinder power errors were less than 0.1 D. COAS repeatability coefficients were better than 0.25 D, and instrument myopia was less than 0.4 D. These were comparable with those of autorefraction. Higher-order repeatability was sufficient to allow reliable measurement of normal third-order aberrations and spherical aberration. Accuracy, repeatability, and instrument myopia of the COAS are similar to those of a conventional autorefractor. Accuracy and repeatability are also similar to those of subjective refraction. Like an autorefractor, the COAS provides instantaneous, objective measurements of sphere and astigmatism, but it also measures higher-order aberrations. We found that it is capable of reliably measuring problematic higher-order aberrations and is therefore a valuable asset for modern clinical eye care.
Monochromatic aberrations as afunctionofage,fromchildhoodtoadvancedage
  • I Brunette
  • Jm Bueno
  • M Parent
Brunette I, Bueno JM, Parent M, et al. Monochromatic aberrations as afunctionofage,fromchildhoodtoadvancedage.InvestOphthalmol Vis Sci 2003; 44:5438–544
Wavefront analysis in normal refractive surgery candidates
  • M V Netto
  • Jr
  • T T Shen
  • S E Wilson
Netto MV, Ambró sio R Jr, Shen TT, Wilson SE. Wavefront analysis in normal refractive surgery candidates. J Refract Surg 2005; 21:332-338
Effect of aging on the monochromatic aberrations of the human eye
  • Ri Calver
  • Mj Cox
  • Db Elliot
Calver RI, Cox MJ, Elliot DB. Effect of aging on the monochromatic aberrations of the human eye. J Opt Soc Am A Opt Image Vis Sci 1999; 16:2069-2078
  • Zernike
  • Rms
  • Errors
ZERNIKE COEFFICIENTS AND RMS WAVEFRONT ERRORS IN NORMAL EYES J CATARACT REFRACT SURG -VOL 32, DECEMBER 2006