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The optical system of the human eye consists of three main components, i.e., the cornea, the crystalline lens and the iris. The iris controls the amount of light coming into the retina by regulating the diameter of the pupil. Therefore, the pupil of the eye acts as the aperture of the system. The optical axis of the eye (dotted grey line) is defined as the line joining the centers of curvature of all the optical surfaces. However, the appropriate and convenient axis that should be used for describing the optical system of the eye is the line of sight (dashed black line), which is defined as the ray that passes through the center of the entrance pupil and strikes the center of the fovea (i.e., the foveola).

The optical system of the human eye consists of three main components, i.e., the cornea, the crystalline lens and the iris. The iris controls the amount of light coming into the retina by regulating the diameter of the pupil. Therefore, the pupil of the eye acts as the aperture of the system. The optical axis of the eye (dotted grey line) is defined as the line joining the centers of curvature of all the optical surfaces. However, the appropriate and convenient axis that should be used for describing the optical system of the eye is the line of sight (dashed black line), which is defined as the ray that passes through the center of the entrance pupil and strikes the center of the fovea (i.e., the foveola).

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Adaptive optics (AO) is a technology used to improve the performance of optical systems by reducing the effects of optical aberrations. The direct visualization of the photoreceptor cells, capillaries and nerve fiber bundles represents the major benefit of adding AO to retinal imaging. Adaptive optics is opening a new frontier for clinical research...

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... available OCT devices, however, cannot provide sufficiently clear images of individual nerve fiber bundles to identify the specific structural abnormality that underlies the pathogenesis of glaucoma [161,162]. Adding AO to imaging systems such as flood-illuminated ophthalmoscopes, SLO equipment or OCT has recently allowed researchers to identify individual nerve fiber bundles [163][164][165], providing high-resolution images of both the RNFL and the ONH (Figure 10). Takayama et al. [163], using an AOSLO, measured the individual nerve fiber bundles width in a population of twenty healthy adults. ...
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... the central retina, the hyperreflective bundles nasal to the fovea were narrower than those above or below the fovea. Figure 10. (A) The optic nerve head of the left eye in a healthy subject (26 years old female). ...

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... For example, high-resolution ophthalmic devices for imaging the retina at the cellular level would be desirable for investigating pathologic tissue changes with micrometer accuracy and for tracking response to prevention strategies in advance with respect to current diagnostic tools. Adaptive optics retinal imaging has the potential to establish a novel methodology for screening patients at risk of AMD progression and to monitor the therapeutic effect of prevention strategies (18). In addition, diagnostic tools for measuring the xanthophyll pigments in situ would be desirable for elucidating and assessing the protective effect of prevention strategies based upon supplementation with lutein. ...
... The Carotenoids in Age-Related Eye Disease Study (CAREDS) concluded that luteinand zeaxanthin-rich diets could protect against intermediate AMD in female participants <75 years of age (19). The Blue Mountain Eye Study reported that high dietary xanthophylls intake reduces the risk of AMD progression over 5-10 years (18,57), patients in the top tertile of intake (≥1 mg/day) had a decreased risk of incident neovascular AMD, and those with above median intakes (743 µg/day) had a reduced risk of indistinct soft or reticular drusen when compared with the remaining population. In the Age-Related Eye Disease Study (AREDS), dietary xanthophylls intake (as determined by a food habit questionnaire at enrollment) was inversely associated with neovascular AMD (OR: 0.65), geographic atrophy (OR: 0.45), and large or extensive intermediate drusen (OR: 0.73) when the highest vs. lowest quintiles were compared (58). ...
... Adaptive optics (AO) is a technology used to improve the performance of optical systems by reducing the effects of optical distortions. It provides considerable improvements in the contrast and sharpness of retinal images that are normally degraded by ocular aberrations when combined with any one of the known imaging modalities (e.g., fundus camera, SLO, OCT) (18). The benefit of AO for high-resolution retinal imaging has been clearly shown in numerous reports with the discovery of differences in the pattern of the cone/rod mosaic in various diseases, including AMD, diabetic retinopathy, inherited retinal dystrophies, and glaucoma (78). ...
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Age-related macular degeneration (AMD) is a chronic multifactorial eye disease representing the primary cause of vision loss in people aged 60 years and older. The etiopathogenesis of the disease remains uncertain, with several risk factors contributing to its onset and progression, such as genotype, aging, hypertension, smoking, overweight, and low dietary intake of carotenoids. Since the aging populations of the industrialized world are increasing rapidly, the impact of AMD in the socio-economical life-developed countries is expected to increase dramatically in the next years. In this context, the benefits of prevention and early disease detection for prompt and effective treatment can be enormous to reduce the social and economic burden of AMD. Nutritional and lifestyle changes, including dietary intake of xanthophyll pigments, such as lutein and zeaxanthin, no smoking, and regular exercise, are known to protect from risk of AMD progression from early to advanced disease stages. In this review, we present the clinical outcomes of a pilot study on trans-scleral iontophoresis delivery of lutein in patients with AMD. Topical delivery of lutein directly to the macula may provide a more efficient method for enriching the macular pigment and for achieving greater patient compliance to therapy than oral administration and thus enhancing prevention strategies. Modern diagnostic methodologies shall address the major problem of accurately detecting the risk of transition from intermediate AMD to advanced AMD stages. Adaptive optics retinal imaging and resonance Raman spectroscopy are two highly promising technologies for the objective assessment of patients with AMD. In this review, we present some of their clinical applications for collecting quantitative measurements of retinal cellular changes and macular content of xanthophyll pigments, respectively. In conclusion, there is great expectation that technological advancements in AMD management will deliver improved screening, therapeutic prevention, and diagnostic systems in the coming decade through a pro-active strategy of “treatment for prevention” that will aim to reduce the global burden of vision loss caused by AMD in the elderly.
... 6 Adaptive optics (AO) is an innovative technology that allows the acquisition of quasi-histologic photoreceptor images of a resolution up to 2 μm making cells visible as single elements. 7,8 A decrease in cone density has already been reported using AO imaging in CSCR patients. [9][10][11] Till date, it is considered the best in-vivo imaging technique for human photoreceptors, nevertheless, there are some limitations of AO which restrict the use in clinical settings such as limited scanning field, separate set-up for clinical imaging, higher cost and long acquisition time. ...
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Purpose To visualize photoreceptors using the Spectralis High Magnification Module (HMM) in a case of central serous chorioretinopathy (CSCR) and to correlate the findings with those of optical coherence tomography (OCT) and optical coherence tomography angiography (OCT-A). Observations A 35-year-old Caucasian male presenting with chronic CSCR in the left eye was examined using HMM, OCT and OCT-A. The photoreceptors mosaic was assessed both in diseased and apparently uninvolved areas. A partial topographic correlation between the loss of photoreceptors on HMM images and an altered reflectivity of the photoreceptor layer on en-face OCT was noted. Interestingly, a correlation between the photoreceptor damage on HMM and choriocapillaris flow-void areas on OCT-A was seen. Conclusions and Importance HMM is a non-invasive imaging modality, allowing the in-vivo visualization of photoreceptor damage in a diseased retina. A focal abnormal perfusion of the choriocapillaris might influence the integrity of the overlying photoreceptors in CSCR.
... O ptical aberrations play a major role in the image quality perceived by the human retina. [1][2][3] There are various aberrations which consist of lower-and higher-order aberrations (HOAs) (LOAs and HOAs). Ninety-two percentage of vision correction is achieved by correcting the LOAs (defocus and astigmatism), whereas 7%-8% are still uncorrected and consist of HOAs such as coma, trefoil, and spherical aberrations. ...
Article
Purpose: The aim of this work is to determine and compare the distribution and influence of higher-order aberrations (HOAs) both clinically and experimentally between different refractive errors. Methods: Commercially available Shack-Hartmann aberrometer was employed to measure the HOA clinically in human eyes. Experimentally, HOA was measured in a model eye by simulating various refractive errors by constructing an aberrometer based on the same Shack Hartmann principle. One-way analyses of variance and simple regression were employed to analyze the distribution and influence of HOA among various refractive errors. Results: A total of 100 eyes were clinically measured for aberrations, of which 35, 50, and 15 eyes were emmetropes, myopes, and hyperopes, respectively. Out of the total root mean square (RMS) value, the HOAs found in the human eyes were 23%, 7%, and 26% and in the model eye, it was 20%, 8%, and 10% between emmetropes, myopes, and hyperopes, respectively. The mean higher-order RMS was almost similar between the groups and among various refractive errors. There was no statistical significance between the individual Zernikes except for the coma in both human and model eyes. Conclusion: The mean HOA is similar amidst the different refractive errors. The presence of 23% HOA in emmetropes signifies that larger part of the human eye is capable of complying with HOA without compromising the image quality. This work signifies that HOA does not play an important role in image clarity for human eyes with regular refractive surface unlike irregular refractive surfaces.
... A meta-analysis of 44 cross-sectional studies reported a significant reduction in the macular vascular density and alterations in retinal microvasculature in patients with DM without clinical DR compared to healthy controls [210]. Further after the advent of adaptive optics which overcomes natural ocular aberrations to provide very high-resolution images, a lot of subclinical evidence of DR has now been generated [211]. Therefore, the absence of DRV at the time of occurrence of DRN in those previous studies may have simply been a clinical assumption. ...
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Purpose To review the evidence supporting diabetic retinal neurodegeneration (DRN) as a form of diabetic retinopathy. Method Review of literature. Results DRN is recognized to be a part of retinopathy in patients with diabetes mellitus (DM), in addition to the well-established diabetic retinal vasculopathy (DRV). DRN has been noted in the early stages of DM, before the onset of clinically evident diabetic retinopathy. The occurrence of DRN has been confirmed in animal models of DM, histopathological examination of donor’s eyes from diabetic individuals and assessment of neural structure and function in humans. DRN involves alterations in retinal ganglion cells, photoreceptors, amacrine cells and bipolar cells, and is thought to be driven by glutamate, oxidative stress and dysregulation of neuroprotective factors in the retina. Potential therapeutic options for DRN are under evaluation. Conclusions Literature is divided on the temporal relation between DRN and DRV, with evidence of both precedence and simultaneous occurrence. The relationship between DRN and multi-system neuropathy in DM is yet to be evaluated critically.
... Adaptive Optics Camera (AOC) fundus images were obtained using a commercially available flood-illumination AOC retinal camera (rtx1™; Imagine Eyes, Orsay, France) [20]. Image acquisition was performed on the right eye starting at the optic disc and up to the first or second branch of the main superior temporal artery to include at least one bifurcation in the acquired field. ...
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Background Ageing, hypertension and diabetes have an intricate effect on microvascular structure. In the retina, the respective contribution of remodeling and hypertrophy in such process is still unclear. We aimed at disentangling age, blood pressure and glycaemia effects on retinal microcirculation using the non-invasive adaptive optics ophthalmoscopy (AOO).Methods We included 429 subjects, distributed into 4 groups according to normal (nBP) or high blood pressure (hBP) and/or normal (nGly) or high fasting glycaemia (hGly). The nBP/nGly group was stratified in age tertiles to isolate the effect of ageing. AOO was used to measure arteriolar wall thickness (WT, µm), arteriolar (aID, µm) and venular internal diameter (vID, µm) and calculate arteriolar wall-to-lumen ratio (WLR), wall cross-sectional area (WCSA, µm2). One-way ANOVA for parametric variables and Kruskal–Wallis test for non-parametric variables were used for comparison among groups. A multivariate regression analysis including age, gender, BP, hGly and antihypertensive treatment was performed to calculate independent predictors of retinal remodeling.ResultsWT was increased with ageing (tertile1: 22.5 ± 3.2, tertile2: 24.2 ± 3.5, tertile 3: 25.2 ± 3.8, p = 0.001) and BP (hBP: 25.2 ± 4.1 vs nBP: 23.9 ± 3.7, p = 0.003). aID decreased with BP (hBP: 90.2 ± 13.4 vs nBP: 93.6 ± 11.6, p = 0.013) and increased with glycaemia (hGly: 97.7 ± 12.5 vs nGly: 93.6 ± 11.6, p = 0.002). A multivariate analysis showed independent association of hBP with WLR; hGly with WCSA; ageing with WLR and WCSA.ConclusionsAOO non-invasively identifies retinal structural changes in human confirming that microvascular remodeling is exclusively related to hypertension, whereas vascular growth is related to ageing and hyperglycaemia.
... In addition, AO is not widely used in clinical work because it is complex, costly and time-consuming, which hinders ophthalmologists exploring ocular microstructures. [12,16] Heidelberg Engineering recently launched the non-invasive Spectralis High Magnification Module (HMM), which optimally uses confocal scanning laser ophthalmoscopy (cSLO) technology to obtain highresolution images of the retina by reducing intraocular light scattering. As an innovative imaging modality, HMM may detect retinal microstructures more easily and quickly than AO. ...
... Although AO technology is known as a feasible method of detecting retinal microstructures, its application is currently very limited in clinical practice due to the specificity and complexity of the device itself. [12,16] In contrast, HMM can be incorporated with a widely used Spectralis Multimodal Imaging Platform, making it easier for ophthalmologists to detect retinal microstructures during daily clinical routines. In terms of efficiency, the HMM has a distinct advantage over AO, in which the HMM can directly obtain 8 • x 8 • degrees of high-resolution images (2.3 mm x 2.3 mm) in a few minutes. ...
Article
Purpose To quantitatively evaluate the photoreceptor density in chronic central serous chorioretinopathy (cCSC) using the Spectralis High Magnification Module (HMM). Methods Twenty-four eyes of 24 patients with resolved cCSC, 24 fellow eyes from 24 other patients with unilateral cCSC, and 24 normal eyes of 24 healthy clients were enrolled in this observational case study. Photoreceptor densities of the retina in the nasal, temporal, superior, and inferior areas 500 μm from the central fovea were counted manually through the High Magnification Module (HMM) images using ImageJ software, and the average values were taken for further analysis. Results The mean photoreceptor density 500 μm from the central fovea in the normal eyes (17217 ± 1144/mm²) was significantly higher than that of both affected eyes (9721 ± 1699/mm²) and fellow eyes (15667 ± 1909/mm²) (P < 0.001; P = 0.002, respectively). The mean photoreceptor density was significantly correlated with best-corrected visual acuity (BCVA, r = -0.432, P = 0.035), duration of symptoms (r = -0.537, P = 0.007), retinal sensitivity (RS) and fixation stability P2 in eyes with resolved cCSC (r = 0.430, P = 0.036; r = 0.420, P = 0.041, respectively). Conclusions The HMM images revealed significant photoreceptor loss in patients with cCSC. The findings suggest that early intervention of the affected eyes, with short duration and good visual function, might be beneficial in preserving photoreceptor cells. As a novel imaging modality producing fast, high-resolution images, HMM shows great potential to detect microstructural impairments in retinal diseases.
... The new SDOCT devices with high resolution give near histological information of the retinal layers with the added advantage of being non-invasive and allowing longitudinal follow-up. Adaptive optics imaging can accurately estimate cone count in healthy and diseased retina [9][10][11][12][13]. It can therefore be used to non-invasively quantify photoreceptor damage, predict prognosis, or document spontaneous resolution in solar retinopathy patients. ...
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Background To study the characteristics of photoreceptors on adaptive optics (AO) in patients of solar retinopathy and its correlation to changes in spectral domain optical coherence tomography (SDOCT) and visual acuity. Methods and material This is a cross-sectional observational study of six eyes of five patients with clinically diagnosed solar retinopathy. Five age-matched controls were included for comparison. A flood-illuminated adaptive optics retinal camera (AO; rtx1, Imagine Eyes, Orsay, France) was used to image the photoreceptors and a spectral domain optical coherence tomography (SDOCT; Spectralis™ Heidelberg Engineering, Germany) was used to study the retinal layers in these patients. The corrected distance visual acuity (CDVA) was assessed using Snellen’s chart. Results Defects on the SDOCT were smaller (0.25 to 0.75°) at the fovea compared with AO (more than 1°). The cone mosaic was preserved beyond 1°. The cone count from the foveal center at 0.75, 1, 2, and 3° was decreased in all patients of solar retinopathy (mean value 5352) compared with age-matched controls (mean value 15693). A corresponding increase in spacing (mean value 19.13) compared with controls (mean value 9.34) was also observed. The CDVA ranged from 20/30 to 20/80. There was no statistically significant relationship between cone density, at any of the eccentricities measured, with CDVA or OCT defect (p > 0.05, for all). Conclusions Adaptive optics is a sensitive and accurate tool to analyze photoreceptor damage in solar maculopathy. It can be used as an adjunct for better understanding of the pathology and to observe or predict changes in these patients.
... Ryc. 2. Schemat budowy oftalmoskopu z szerokopolowym oświetleniem (flood illumination) z dołączoną OA. Jest to również schemat funduskamery z dołączoną OA [9] Ryc. 3. Ręczny skaningowy laserowy konfokalny oftalmoskop z OA [10] Ryc. 5. Pseudotrójwymiarowy wykres funkcji apodyzacyjnej źrenicy stosowanej w opisie efektu Stilesa-Crawforda I rodzaju (A); zmiany położenia czopków związane z układaniem się ich wzdłuż kierunku, z którego dochodzi światło (B) [11] ...
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Optykę adaptywną stosowaną w naukach o widzeniu wyróżnia pewna cecha niespotykana w innych jej zastosowaniach. Jest nią swego rodzaju dwukierunkowość. Z jednej strony pozwala ona zajrzeć w głąb oka i uzyskać obrazy, także trójwymiarowe, struktur tkankowych o tak dobrej jakości, jak gdyby elementy optyczne oka zaangażowane w tworzenie tych obrazów były niemal zupełnie pozbawione aberracji monochromatycznych, z drugiej zaś pozwala zaproponować taką korekcję, która w efekcie da obraz siatkówkowy otaczającego świata o ostrości nieosiągalnej dla najlepiej dobranej korekcji sferocylindrycznej. Szacuje się, że dzięki tej korekcji będzie możliwe osiąganie ostrości o dwa rządki poniżej rządka zerowego na tablicach optotypów logMAR. W związku z tym ukuty został termin superwidzenie. Nie należy go mylić z hiperostrością, którą jest np. ostrość vernier. W tym ocinku cyklu będziemy zaglądać w głąb oka wspierani optyką adaptywną. ........................................................ OPTYKA - branżowy dwumiesięcznik, issue 2(69)2021, pp. 74-78
... Advances in retinal imaging devices and the development of more sophisticated optical systems have made it possible to capture enface images of photoreceptors and microcirculation. Adaptive optics (AO) is a noninvasive method for visualizing microcirculation and retinal structures with resolution comparable to those achieved in histological studies [16][17][18]. e rtx1 TM (Imagine Eyes, Orsay, France) is a microscope that uses AO technology. e AO imaging system corrects aberrations arising from various refractive surfaces within the eye. ...
... e AO imaging system corrects aberrations arising from various refractive surfaces within the eye. e rtx1 microscope includes image acquisition and object recognition software for image analysis oriented towards cones and vessels [16]. e available international literature offers several publications that examine findings using the rtx1 in healthy patients [18][19][20][21][22]. ...
Article
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Background: Overweight and obese patients are at risk for diabetes, cardiovascular disorders, and microvascular complications. The rtx1TM (Imagine Eyes, France) is a microscope that allows near histological visualizations of cones and retinal microcirculation. Objective: This study analysed the cones and retinal microvascular changes in a group of 47 healthy women with different BMI values. Participants were divided into 2 groups: the BMI group (28 women with BMI >/25) and the control group (19 lean women with BMI <25). Results: The lumen and diameter of retinal arteries were not significantly different between groups. There were significant differences in the thickness of arteriole walls. The WLR and WCSA values differed significantly between the control and BMI groups (for WLR 0.25 ± 0.03 vs. 0.29 ± 0.03, p < 0.001; for WCSA 4136.7 ± 1140.0 vs. 5217.3 ± 944.0, respectively, p < 0.001). In healthy eyes, cone density and morphology were not affected by weight. Conclusions: Retinal image analysis with rtx1 offers a novel noninvasive measurement of early changes in retinal vasculature that are not detectable during routine clinical examination. Abnormalities of retinal arterioles found by rtx1™examination should be considered as a strong risk factor for cardiovascular changes resulting from overweight and obesity.
... Adaptive optics (AO) is a technology that allows to correct for these aberrations and thus vastly increases the resolution of any imaging method in which it is implemented [1][2][3][4]. Currently, the most commonly used AO enhanced imaging technologies are AO flood illumination fundus camera (AO-FC) and AO scanning laser ophthalmoscopy (AO-SLO), which have both been applied on healthy eyes and in several retinal pathologies [5][6][7][8][9][10][11]. ...
Article
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Purpose To assess the signal composition of cone photoreceptors three-dimensionally in healthy retinas using adaptive optics optical coherence tomography (AO-OCT). Methods Study population. Twenty healthy eyes of ten subjects (age 23 to 67). Procedures. After routine ophthalmological assessments, eyes were examined using AO-OCT. Three-dimensional volumes were acquired at 2.5° and 6.5° foveal eccentricity in four main meridians (superior, nasal, inferior, temporal). Cone densities and signal compositions were investigated in four different planes: the cone inner segment outer segment junction (IS/OS), the cone outer segment combined with the IS/OS (ISOS+), the cone outer segment tips (COST) and full en-face plane (FEF) combining signals from all mentioned cone layers. Additionally, reliability of a simple semi-automated approach for assessment of cone density was tested. Main outcome measures. Cone density of IS/OS, IS/OS+, COST and FEF. Qualitative depiction and composition of each cone layer. Inter-rater agreement of cone density measurements. Results Mean overall cone density at all eccentricities was highest at the FEF plane (21.160/mm ² ), followed by COST (20.450/mm ² ), IS/OS+ (19.920/mm ² ) and IS/OS (19.530/mm ² ). The different meridians and eccentricities had a significant impact on cone density, with lower eccentricity resulting in higher cone densities (p≤.001), which were highest at the nasal, then temporal, then inferior and then superior meridian. Depiction of the cone mosaic differed between all 4 layers regarding signal size and packing density. Therefore, different cone layers showed evident but not complete signal overlap. Using the semi-automated technique for counting of cone signals achieved high inter-rater reliability (ICC > .99). Conclusions In healthy individuals qualitative and quantitative changes in cone signals are found not only in different eccentricities and meridians, but also within different photoreceptor layers. The variation between cone planes has to be considered when assessing the integrity of cone photoreceptors in healthy and diseased eyes using adaptive optics technology.