[Show abstract][Hide abstract] ABSTRACT: To evaluate repeatability and reproducibility of anterior corneal power measurements obtained with a new corneal topographer OphthaTOP (Hummel AG, Germany) and agreement with measurements by a rotating Scheimpflug camera (Pentacam HR, Oculus, Germany) and an automated keratometer (IOLMaster, Carl Zeiss Meditec, Germany).
The right eyes of 79 healthy subjects were prospectively measured three times with all three devices. Another examiner performed three additional scans with the OphthaTOP in the same session. Within one week, the first examiner repeated the measurements using the OphthaTOP. The flat simulated keratometry (Kf), steep K (Ks), mean K (Km), J0, and J45 were noted. Repeatability and reproducibility of measurements were assessed by within-subject standard deviation (Sw), repeatability (2.77 Sw), coefficient of variation (CoV), and intraclass correlation coefficient (ICC). Agreement between devices was assessed using 95% limits of agreement (LoA).
Intraobserver repeatability and interobserver and intersession reproducibility of all measured parameters showed a 2.77 Sw of 0.29 diopter or less, a CoV of less than 0.24%, and an ICC of more than 0.906. Statistically significant differences (P<0.001) were found between the parameters analyzed by the three devices, except J0 and J45. The mean differences between OphthaTOP and the other two devices were small, and the 95% LoA was narrow for all results.
The OphthaTOP showed excellent intraobserver repeatability and interobserver and intersession reproducibility of corneal power measurements. Good agreements with the other two devices in these parameters were found in healthy eyes.
PLoS ONE 01/2015; 10(1):e109414. · 3.53 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: To determine the repeatability and reproducibility of measurements of central corneal thickness (CCT) using optical low-coherence reflectometry (Lenstar LS900; Haag Streit) in normal eyes and post-femtosecond laser in situ keratomileusis (post-FS-LASIK) eyes and evaluate their agreement with ultrasound (US) pachymetry.
CCT was measured using Lenstar and US pachymetry sequentially in normal and post-FS-LASIK eyes by 2 experienced observers. Intraoperator repeatability and interoperator reproducibility were assessed by within-subject standard deviation, test-retest repeatability, coefficient of variation (CoV), and intraclass correlation coefficient. Paired t-tests and Bland-Altman plots were used for analyzing agreement between the 2 devices.
In this study, 55 healthy subjects and 50 post-FS-LASIK patients were recruited. Test-retest repeatability of Lenstar was within 10 μm, CoV was less than 1.0%, and intraclass correlation coefficient was more than 0.9 in both normal and post-FS-LASIK groups. Mean difference between these methods was 1.4 ± 4.2 μm and -1.7 ± 5.4 μm, respectively. Moreover, measurements of CCT showed narrow 95% limits of agreement (range, normal group: -6.8 and 9.6 μm; post-FS-LASIK group: -12.4 and 8.9 μm), which implied good agreement.
Measurements of CCT using Lenstar showed excellent intraoperator repeatability and interoperator reproducibility both in normal eyes and post-FS-LASIK eyes. Measurements of CCT using Lenstar and US pachymetry showed good agreement and both can be used interchangeably.
[Show abstract][Hide abstract] ABSTRACT: The aim of this study was to evaluate the repeatability of central corneal thickness (CCT) measurements in normal eyes using 2 new noncontact specular microscopes (NCSMs) EM-3000 (Tomey, Japan) and SP-02 (CSO, Italy) and to compare the results with those obtained from an SP-3000P NCSM (Topcon, Japan) and ultrasound pachymetry (USP).
Seventy subjects were enrolled in a prospective study. A single experienced ophthalmologist performed tests with each of the 4 instruments. Measurements were obtained in the right eye during the same session. The testing sequence of the NCSM was randomly selected. After performing noncontact examinations, the USP was performed to derive the CCT measurements. Intraoperator repeatability was analyzed using within-subject coefficient of variation and intraclass correlation coefficients. The agreement between NCSMs or NCSM and USP was assessed with Bland-Altman plots and 95% limits of agreement (LoA).
The mean CCT values measured by SP-3000P, EM-3000, SP-02, and USP were 513.66 ± 33.14 μm, 529.12 ± 33.22 μm, 549.06 ± 40.27 μm, and 539.01 ± 35.73 μm, respectively. All coefficients of variation were <1.3%, and the intraclass correlation coefficients were >0.95. There were statistically significant differences between any 2 devices as determined by CCT measurements. The mean difference between paired comparisons was >9 μm. The 95% LoA ranges were broad, and the greatest 95% LoA was found to exist between SP-3000P and SP-02.
The new NCSMs and USP all show a high intraoperator repeatability for CCT measurements in normal eyes. However, interdevice agreement was poor and prevented the comparison of CCT measurements taken with different instruments.
[Show abstract][Hide abstract] ABSTRACT: To evaluate the effect of posterior scleral reinforcement in controlling high myopic axial progression in young patients.
Only one eye of each patient had posterior scleral reinforcement surgery. Before surgery and at each postoperative follow-up, the best corrected visual acuity, intraocular pressure, refractive errors, indirect ophthalmoscopy, B-type ultrasonography, and IOLMASTER reflected light biometry were performed on both eyes. The changes of axial length and the changes of refractive errors from the baseline were compared between the surgery eyes and the contralateral eyes.
Thirty patients had a mean age of 7.5 years and a mean spherical equivalent of -9.72 diopters. The mean elongation of axial length was significantly less in the surgery eye group than that in the contralateral eye group (0.75 mm vs. 0.94 mm, p < 0.0001, paired t test) after a mean follow-up of 895 days. The surgical effect was mild but maintained during the follow-up. The eyes with staphyloma gained less surgical effect when compared with the eyes without staphyloma (p = 0.0036). There was also a notable nonstatistically significant trend for younger patients to gain a larger surgical effect (p = 0.0986).
Posterior scleral reinforcement surgery was found effective in slowing down high myopic axial progression in young patients within the study period, but the size of the effect was small. The surgical procedure is well tolerated without vision-threatening complications.
Optometry and vision science: official publication of the American Academy of Optometry 02/2014; · 1.53 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Purpose. To assess the consistency of anterior segment measurements obtained using a Sirius Scheimpflug/Placido photography-based topography system (CSO, Italy) and IOLMaster partial coherence interferometry (Carl Zeiss Meditec, Germany) in eyes with cataracts. Methods. A total of 90 eyes of 90 patients were included in this prospective study. The anterior chamber depth (ACD), keratometry (K), corneal astigmatism axis, and white to white (WTW) values were randomly measured three times with Sirius and IOLMaster. Concordance between them was assessed by calculating 95% limits of agreement (LoA). Results. The ACD and K taken with the Sirius were statistically significantly higher than that taken with the IOLMaster; however, the Sirius significantly underestimated the WTW values compared with the IOLMaster. Good agreement was found for Km and ACD measurements, with 95% LoA of -0.20 to 0.54 mm and -0.16 to 0.34 mm, respectively. Poor agreement was observed for astigmatism axis and WTW measurements, as the 95% LoA was -23.96 to 23.36° and -1.15 to 0.37 mm, respectively. Conclusion. With the exception of astigmatism axis and WTW, anterior segment measurements taken by Sirius and IOLMaster devices showed good agreement and may be used interchangeably in patients with cataracts.
Journal of Ophthalmology 01/2014; 2014:540760. · 1.94 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: To investigate the bilateral symmetry of the global corneal topography in normal corneas with a wide range of curvature, astigmatism and thickness values.
Topography images were recorded for the anterior and posterior surfaces of 342 participants using a Pentacam. Elevation data were fitted to a general quadratic model that considered both translational and rotational displacements. Comparisons between fellow corneas of estimates of corneal shape parameters (elevation, radius in two main directions, Rx and Ry, and corresponding shape factors, Qx and Qy) and corneal position parameters (translational displacements: x0, y0 and z0, and rotational displacements: α, β and γ) were statistically analyzed.
The general quadratic model provided average RMS of fit errors with the topography data of 1.7±0.6 µm and 5.7±1.3 µm in anterior and posterior corneal surfaces. The comparisons showed highly significant bilateral correlations with the differences between fellow corneas in Rx, Ry, Qx and Qy of anterior and posterior surfaces remaining insignificantly different from zero. Bilateral differences in elevation measurements at randomly-selected points in both corneal central and peripheral areas indicated strong mirror symmetry between fellow corneas. The mean geometric center (x0, y0, z0) of both right and left corneas was located on the temporal side and inferior-temporal side of the apex in anterior and posterior topography map, respectively. Rotational displacement angle α along X axis had similar distributions in bilateral corneas, while rotation angle β along Y axis showed both eyes tilting towards the nasal side. Further, rotation angle γ along Z axis, which is related to corneal astigmatism, showed clear mirror symmetry.
Analysis of corneal topography demonstrated strong and statistically-significant mirror symmetry between bilateral corneas. This characteristic could help in detection of pathological abnormalities, disease diagnosis, measurement validation and surgery planning.
PLoS ONE 08/2013; 8(8):e73412. · 3.53 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Optical coherence tomography (OCT) images can provide quantitative measurements of the eye's entire anterior segment. A new technique founded on a newly proposed level set-based shape prior segmentation model has been developed for automatic segmentation of the cornea's anterior and posterior boundaries. This technique comprises three major steps: removal of regions containing irrelevant structures and artifacts, estimation of the cornea's location using a thresholding technique, and application of the new level set-based shape prior segmentation model to improve segmentation. The performance of our technique is compared to previously developed methods for analysis of the cornea in 33 OCT images of normal eyes, whereby manual annotations are used as a reference standard. The new technique achieves much improved concordance than previous methods, with a mean Dice's similarity coefficient of >0.92. This demonstrates the technique's potential to provide accurate and reliable measurements of the anterior segment geometry, which is important for many applications, including the construction of representative numerical simulations of the eye's mechanical behavior.
Journal of Biomedical Optics 05/2013; 18(5):56003. · 2.75 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The biomechanical changes in rabbit cornea preserved in storage media with different glucose concentrations are experimentally assessed. Two groups of eight fresh rabbit corneas were preserved for 10 days in storage medium Optisol-GS with glucose concentrations of 14 and 28 mM, respectively. Eight additional corneas preserved, glucose-free, in the same medium served as the control group. All specimens were tested under inflation conditions up to 45 mmHg posterior pressure, and the pressure-deformation data obtained experimentally were analyzed using shell theory to derive the stress-strain behavior. Comparisons were held between the three specimen groups in order to determine the effect of glucose concentration on corneal biomechanical behavior and thickness. After storage, the mean central corneal thickness in the control, low-glucose and high-glucose groups underwent statistically significant increases of 38.7 ± 11.3%, 45.4 ± 7.6% and 50.6 ± 8.6%, respectively. The corneas also demonstrated consistent stiffness increases with higher glucose concentrations. The tangent modulus values determined at different pressure levels between 10 and 40 mmHg underwent statistically significant increases with glucose level (P < 0.05). Compared to the control group, other specimens had higher tangent modulus by 17-20% on average with low glucose and 30-37% with high-glucose concentration. The results of the study indicate that the influence of the high-glucose level commonly experienced in diabetes on the biomechanical stiffness of the cornea should be considered in clinical management and in understanding corneal ectasia, glaucoma and the response to refractive surgery.
Experimental Eye Research 02/2011; 92(5):353-60. · 3.02 Impact Factor