Faculty Bibliography

PURPOSE: To investigate repeatability of steep and flat keratometry measurements, as well as astigmatism axis in cohorts with normal range and regular astigmatic such as: eyes following laser-assisted in situ keratomileusis (LASIK) and normal population, as well as cohorts of high and irregular astigmatism such as keratoconic eyes, and keratoconic eyes following corneal collagen cross-linking, employing a novel corneal reflection topography device. METHODS: Steep and flat keratometry and astigmatism axis measurement repeatability was investigated employing a novel multicolored-spot reflection topographer (Cassini) in four study groups, namely a post myopic LASIK-treated Group A, a keratoconus Group B, a post-CXL keratoconus Group C, and a control Group D of routine healthy patients. Three separate, maps were obtained employing the Cassini, enabling investigation of the intra-individual repeatability by standard deviation. Additionally we investigated in all groups,the Klyce surface irregularity indices for keratoconus, the SAI (surface asymmetry index) and the SRI (surface regularity index). RESULTS: Flat keratometry repeatability was 0.74+/-0.89 (0.03 to 5.26) diopters (D) in the LASIK Group A, 0.88+/-1.45 (range minimum to maximum, 0.00 to 7.84) D in the keratoconic Group B, and 0.71+/-0.94 (0.02 to 6.23) D in the cross-linked Group C. The control Group D had flat keratometry repeatability 0.36+/-0.46 (0.00 to 2.71) D. Steep keratometry repeatability was 0.64+/-0.82 (0.01 to 4.81) D in the LASIK Group A, 0.89+/-1.22 (0.02 to 7.85) D in the keratoconic Group B, and 0.93+/-1.12 (0.04 to 5.93) D in the cross-linked Group C. The control Group D had steep keratometry repeatability 0.41+/-0.50 (0.00 to 3.51) D. Axis repeatability was 3.45+/-1.62 degrees (0.38 to 7.78 degrees ) for the LASIK Group A, 4.12+/-3.17 degrees (0.02 to 12.13 degrees ) for the keratoconic Group B, and 3.20+/-1.99 degrees (0.17 to 8.61 degrees ) for the cross-linked Group C. The control Group D had axis repeatability 2.16+/-1.39 degrees (0.05 to 5.86 degrees ). The SAI index measurement repeatability was 0.33+/-0.40 (0.01 to 2.31) in the post-LASIK Group A, 0.39+/-0.75 (0.00 to 7.15) in the keratoconic Group B, and 0.43+/-0.56 (0.05 to 3.50) in the keratoconus post-CXL Group C. The control group had SAI measurement repeatability of 0.26+/-0.30 (0.00 to 2.39). The SRI index repeatability was 0.22+/-0.17 (0.01 to 0.96) for post-LASIK Group A, 0.20+/-0.18 (0.00 to 1.07) in keratoconic Group B, and 0.13+/-0.09 (0.00 to 0.45) in the keratoconus post-CXL Group C. The control Group D had SRI measurement repeatability of 0.23+/-0.16 (0.00 to 0.75). CONCLUSION: This novel corneal topography device appears to offer very high specificity in estimating corneal keratometry and specific corneal irregularity indices, even in topographically challenging corneas such as LASIK treated, keratoconic, and cross-linked.

PURPOSE: To compare postoperative changes in apparent photopic and mesopic pupil size and centration in relation to cornea reflection landmarks after cataract surgery. SETTING: LaserVision.gr Clinical and Research Eye Institute, Athens, Greece. DESIGN: Prospective consecutive case study. METHODS: Pupils were imaged for pupil size and corneal vertex location before and 1-month after cataract surgery. Digital analysis of pupil images was used to determine the Cartesian coordinates (nasal-temporal, horizontal axis, superior-inferior, vertical axis) of the first Purkinje reflection point (approximating the corneal intersection of the visual axis [corneal vertex]) to the pupil geometric center (approximating the corneal intersection of the line of sight [corneal apex]). Pupil size changes were measured, and the correlation between vertex-to-apex shift changes and postoperative pupil centroid shift was evaluated. RESULTS: The study evaluated 40 eyes. The pupil size (diameter) change corresponded to a relative reduction of -9.8% for photopic pupils and -9.1% for mesopic pupils; the difference was statistically significant (P = .045 and P = .011, respectively). Also, there was a reduction in the centroid shift (all eyes) from a mean of 0.12 mm preoperatively to 0.05 mm postoperatively as a result of the postoperative minus temporal horizontal difference between the corneal vertex and the apex. CONCLUSIONS: Cataract extraction surgery appears to affect pupil size and centration. Specifically, a smaller pupil and less temporal shift were recorded. These data may have clinical relevance in targeted intraoperative intraocular lens centration. FINANCIAL DISCLOSURE: Dr. Kanellopoulos is a consultant to Alcon Surgical, Inc., Wavelight Laser Technologie AG, Allergan, Avedro, Inc., and i-Optics Corp. No author has a financial or proprietary interest in any material or method mentioned.

PURPOSE/OBJECTIVE:To report novel application of topographically-customized collagen crosslinking aiming to achieve hyperopic refractive changes. Two approaches were evaluated, one based on epithelium-off and one based on epithelium-on (transepithelial). METHODS:A peripheral annular-shaped topographically customizable design was employed for high-fluence ultraviolet (UV)-A irradiation aiming to achieve hyperopic refractive changes. A total of ten eyes were involved in this study. In group-A (five eyes), a customizable ring pattern was employed to debride the epithelium by excimer laser ablation, while in group-B (also five eyes), the epithelium remained intact. In both groups, specially formulated riboflavin solutions were applied. Visual acuity, cornea clarity, keratometry, topography, and pachymetry with a multitude of modalities, as well as endothelial cell counts were evaluated. RESULTS:One year postoperatively, the following changes have been noted: in group-A, average uncorrected distance visual acuity changed from 20/63 to 20/40. A mean hyperopic refractive increase of +0.75 D was achieved. There was some mild reduction in the epithelial thickness. In group-B, average uncorrected distance visual acuity changed from 20/70 to 20/50. A mean hyperopic refractive increase of +0.85 D was achieved. Epithelial thickness returned to slightly reduced levels (compared to baseline) in group-A, whereas to slightly increased levels in group-B. CONCLUSION/CONCLUSIONS:We introduce herein the novel application of a topographically-customizable collagen crosslinking to achieve a hyperopic refractive effect. This novel technique may be applied either with epithelial removal, offering a more stable result or with a non-ablative and non-incisional approach, offering a minimally invasive alternative.

PURPOSE/OBJECTIVE:To evaluate epithelial thickness profile changes following myopic femtosecond laser-assisted LASIK in relation to the degree of myopia corrected, evaluated with a spectral-domain anterior-segment optical coherence tomography system. METHODS:Sixty-one consecutive cases were observed for corneal epithelial thickness distribution preoperatively and at 1 day, 1 week, 1 month, and 1 year postoperatively. Epithelial thickness mapping was obtained with a spectral-domain optical coherence tomography system (Optovue Inc., Fremont, CA). Descriptive statistics investigated epithelial thickness at the central 2-mm area, the mean over the central 6-mm area, and mid-peripherally at the 5-mm ring area. RESULTS:Preoperatively, the pupil center epithelial thickness was 51.67 ± 2.57 μm (range: 45 to 56 μm), mean was 51.76 ± 2.66 μm (range: 45 to 57 μm), and mid-periphery was 51.78 ± 2.71 μm (range: 46 to 57 μm). Compared to the preoperative values, the epithelial thickness for the center, mean, and mid-periphery was −0.30, +1.07, and +1.35 μm at 1 week, +1.58, +2.88, and +3.31 μm at 1 month (P = .0036, < .001, and < .001), and +1.42, +2.90, and +3.19 μm at 1 year postoperatively (P = 0.146, < .001, and < .001), respectively. The correlation analysis between the epithelial thickness increase and the spherical equivalent of myopic correction showed a trend toward epithelial thickness increase with the amount of myopic ablation, particularly at the mid-peripheral 5-mm area. CONCLUSIONS:In this comprehensive study of postoperative corneal epithelial thickness remodeling following femtosecond laser-assisted myopic LASIK correction, an increase at the 1-month and up to 1-year postoperative interval suggested postoperative epithelial activity in connection to the extent of ablation.

PURPOSE/OBJECTIVE:To investigate refractive, topometric, pachymetric, and visual rehabilitation changes induced by anterior surface normalization for keratoconus by partial topography-guided excimer laser ablation in conjunction with accelerated, high-fluence cross-linking. METHODS:Two hundred thirty-one keratoconic cases subjected to the Athens Protocol procedure were studied for visual acuity, keratometry, pachymetry, and anterior surface irregularity indices up to 3 years postoperatively by Scheimpflug imaging (Oculus Optikgeräte GmbH, Wetzlar, Germany). RESULTS:Mean visual acuity changes at 3 years postoperatively were +0.38 ± 0.31 (range: -0.34 to +1.10) for uncorrected distance visual acuity and +0.20 ± 0.21 (range: -0.32 to +0.90) for corrected distance visual acuity. Mean K1 (flat meridian) keratometric values were 46.56 ± 3.83 diopters (D) (range: 39.75 to 58.30 D) preoperatively, 44.44 ± 3.97 D (range: 36.10 to 55.50 D) 1 month postoperatively, and 43.22 ± 3.80 D (range: 36.00 to 53.70 D) up to 3 years postoperatively. The average Index of Surface Variance was 98.48 ± 43.47 (range: 17 to 208) pre-operatively and 76.80 ± 38.41 (range: 7 to 190) up to 3 years postoperatively. The average Index of Height Decentration was 0.091 ± 0.053 μm (range: 0.006 to 0.275 μm) preoperatively and 0.057 ± 0.040 μm (range: 0.001 to 0.208 μm) up to 3 years postoperatively. Mean thinnest corneal thickness was 451.91 ± 40.02 μm (range: 297 to 547 μm) preoperatively, 353.95 ± 53.90 μm (range: 196 to 480 μm) 1 month postoperatively, and 370.52 ± 58.21 μm (range: 218 to 500 μm) up to 3 years postoperatively. CONCLUSIONS:The Athens Protocol to arrest keratectasia progression and improve corneal regularity demonstrates safe and effective results as a keratoconus management option. Progressive potential for long-term flattening validates using caution in the surface normalization to avoid overcorrection.

PURPOSE/OBJECTIVE:To investigate preoperative and postoperative anterior and posterior keratometry and simulated corneal astigmatism in keratoconic eyes treated with collagen cross-linking combined with anterior surface normalization by partial topography-guided excimer ablation (the Athens Protocol). METHODS:Anterior and posterior corneal keratometry were measured by Scheimpflug imaging for 267 untreated keratoconic eyes. Following treatment, they were assessed 1 year postoperatively. RESULTS:Before treatment, average anterior keratometric value was 47.06 ± 6.02 diopters (D) for flat and 51.24 ± 6.75 D for steep. The posterior keratometric values were -6.70 ± 0.99 D (flat) and -7.67 ± 1.15 D (steep). Anterior astigmatism was on average with-the-rule (-1.97 ± 6.21 D), whereas posterior astigmatism was against-the-rule (+0.53 ± 1.02 D). The posterior and anterior astigmatism were highly correlated (r(2) = 0.839). After treatment, anterior keratometric values were 43.97 ± 5.81 D (flat) and 46.55 ± 6.82 D (steep). Posterior keratometric values were -6.58 ± 1.05 D (flat) and -7.69 ± 1.22 D (steep). Anterior astigmatism was on average with-the-rule (-1.56 ± 3.80 D), whereas posterior astigmatism was against-the-rule (+0.45 ± 1.29 D). The statistically significant (P < .05) keratometric changes indicated anterior surface flattening -3.09 ± 2.67 D (flat) and -4.19 ± 2.96 D (steep). The posterior keratometric changes were not statistically significant (P > .05). CONCLUSIONS:Before treatment, there was a strong correlation between posterior and anterior corneal astigmatism. After treatment, statistically significant anterior keratometric values flattened. The posterior surface keratometric values did not demonstrate statistically significant postoperative change: there was minimal posterior change, despite the significant anterior surface normalization.

PURPOSE/OBJECTIVE:To map corneal and epithelial layer thickness changes following cataract removal surgery employing a spectral-domain anterior-segment optical coherence tomography system. METHODS:Corneal and epithelial thickness three-dimensional profile distribution was clinically imaged preoperatively and up to 3 months postoperatively with anterior-segment optical coherence tomography in 116 consecutive cases. Descriptive statistics investigated central corneal thickness, minimum corneal thickness, and epithelial thickness at the central 2-mm area, the mean over the 6-mm area, and mid-peripherally at 5-mm ring. RESULTS:In comparison to preoperative, the center, mean, and mid-peripheral epithelial thickness at the first postoperative day increased by +2.84, +2.35, and +2.25 μm, respectively (P < .001, < .001, and = .0014). One week postoperatively, the epithelial thickness differences were -1.91, -2.62, and -2.76 μm, respectively (P < .001, < .001, and < .001). Four weeks postoperatively, the differences of -0.20, -0.59, and -0.66 μm for the center, mean, and mid-periphery were not statistically significant (P = .6449, .1512, and .11097). Three months postoperatively, the differences were -0.05, -0.28, and -0.09 μm, respectively (P = .8722, .2341, and .6431). CONCLUSIONS:Qualitative and quantitative assessment of epithelial remodeling following cataract removal indicated that the early (1 day and 1 week) corneal and epithelial thickness returned to the preoperative baseline 4 weeks postoperatively. This in vivo epithelial and corneal screening with optical coherence tomography can be valuable for the postoperative assessment and follow-up.

Purpose: To implement digital analysis of pupil imaging (shape and size) in relation to cornea apex position and compare preoperative and postoperative data to measure the possible pupil shape and centration changes following cataract surgery. Methods: 35 consecutive cataract patients (70 eyes) were digitally imaged pre- and post-operatively by Placido Topography (Vario Topolyzer, WaveLight, Erlagen, Germany) providing pupil imaging and cornea apex identification. Digital analysis implemented on the images investigated the Cartesian coordinates (nasal -temporal being the horizontal, and superior-inferior the vertical axis) of the corneal apex (approximating the intersection of line of sight with the cornea) to the pupil geometric center (approximating the visual axis). The Cartesian changes of the differences were associated with postoperative pupil centroid shift. Results: The photopic pupil measurements indicated a pre-operative temporal location of 0.24 +/- 0.15 (0.03 to 0.44) mm and a superior of 0.01+/-0.14 (-0.22 to +0.18) mm. Postoperatively, the pupil center appeared shifted temporally by 0.15 +/- 0.12 (0.27 to -0.01) mm and superiorly by +0.06 +/- 0.21 (-0.33 to 0.22) mm. The scotopic pupil measurements were preoperatively temporally by 0.28 +/- 0.15 (0.41 to 0.03) mm, and inferiorly by 0.02 +/- 0.20 (-0.24 to 0.29) mm. Postoperatively the pupil center was temporally by 0.20 +/- 0.10 (0.04 to 0.28) mm and superiorly by 0.04 +/- 0.19 (-0.26 to +0.27) mm. Conclusions: Cataract extraction surgery appears to affect pupil centration. Specifically a more nasal (+0.10 mm) and more superior (0.05 mm) shift was recorded. These data may have clinical reference in targeted intraoperative IOL centration

Purpose To evaluate applicability of spectral domain optical coherence tomography (AS-OCT) of epithelial thickness patterns in normal and in the diagnosis of keratoconus, and to compare with Scheimpflug imaging keratoconus severity. Methods 250 healthy (control group-A) and 155 untreated keratoconic (study group-B) eyes were subjected to anterior segment OCT three-dimensional epithelial thickness imaging. Comparative statistical analysis of patterns was performed, investigating central, minimum, inferior, posterior, and topographic variability of epithelial thickness. Epithelial thickness characteristics were correlated to established Scheimpflug imaging-derived keratoconus classification and anterior surface irregularity indices. Results Intra-individual repeatability of epithelial thickness was for group-A +/-1.13 mum, for group-B +/-1.78 mum for center and average +/-1.67 mum (center, superior, inferior, maximum and minimum). In group-A, center epithelial was 52.54+/-3.23 mum, maximum 55.33+/-3.27 mum and minimum 48.50+/-3.98 mum. In group B, center thickness was 51.75+/-7.02 mum, maximum and minimum were 63.54+/-8.85 mum and 40.73+/-8.51 mum. Topographic variability was 6.07+/-3.55 mum (range -22.81+/-12.55 mum) for the keratoconic group-B, while for the control group-A 1.59+/-0.79 mum (-6.86+/-3.33 mum). Epithelial thickness topographic variability and range correlated well with keratoconus severity in the study group-B. Conclusions AS-OCT may o er high predictability of 3 dimensional epithelial assessment in keratoconus. Overall epithelial thickness in keratoconic eyes appears significantly different to normal even in lower stages of keratoconus. Increased overall thickness correlated remarkably with keratoconus severity, as defined by established Scheimpflug imaging-derived anterior-surface irregularity indices

PURPOSE: To investigate epithelial thickness-distribution characteristics in a large group of keratoconic patients and their correlation to normal eyes employing anterior-segment optical coherence tomography (AS-OCT). MATERIALS AND METHODS: The study group (n=160 eyes) consisted of clinically diagnosed keratoconus eyes; the control group (n=160) consisted of nonkeratoconic eyes. Three separate, three-dimensional epithelial thickness maps were obtained employing AS-OCT, enabling investigation of the pupil center, average, mid-peripheral, superior, inferior, maximum, minimum, and topographic epithelial thickness variability. Intraindividual repeatability of measurements was assessed. We introduced correlation of the epithelial data via newly defined indices. The epithelial thickness indices were then correlated with two Scheimpflug imaging-derived AS-irregularity indices: the index of height decentration, and the index of surface variance highly sensitive to early and advancing keratoconus diagnosis as validation. RESULTS: Intraindividual repeatability of epithelial thickness measurement in the keratoconic group was on average 1.67 mum. For the control group, repeatability was on average 1.13 mum. In the keratoconic group, pupil-center epithelial thickness was 51.75+/-7.02 mum, while maximum and minimum epithelial thickness were 63.54+/-8.85 mum and 40.73+/-8.51 mum. In the control group, epithelial thickness at the center was 52.54+/-3.23 mum, with maximum 55.33+/-3.27 mum and minimum 48.50+/-3.98 mum epithelial thickness. Topographic variability was 6.07+/-3.55 mum in the keratoconic group, while for the control group it was 1.59+/-0.79 mum. In keratoconus, topographic epithelial thickness change from normal, correlated tightly with the topometric asymmetry indices of IHD and ISV derived from Scheimpflug imaging. CONCLUSION: Simple, OCT-derived epithelial mapping, appears to have critical potential in early and advancing keratoconus diagnosis, confirmed with its correlation with established Scheimpflug-derived asymmetry topometric indices.