Alain Saad

Topographic and tomographic properties of forme fruste keratoconus corneas.

PURPOSE To investigate the efficacy of topography and tomography indices combined in discriminant functions to detect mild ectatic corneas. METHODS The authors retrospectively reviewed the data of 143 eyes separated into three groups by the Corneal Navigator OPD scanning system (Nidek, Gamagori, Japan): normal (N; LASIK surgery with a 2-year follow-up; n = 72), forme fruste keratoconus (N topography with contralateral KC; FFKC; n = 40), and KC (n = 31). Topography and tomography indices, corneal thickness spatial profile (CTSP), and anterior and posterior curvature spatial profiles were obtained with the Orbscan IIz (Bausch & Lomb Surgical, Rochester, NY). The percentage of thickness increase (PTI) from the thinnest point to the periphery, the percentage of variation of anterior (PVAK), and posterior curvature were calculated and compared by Kruskal-Wallis test. The usefulness of these data to discriminate among the three groups was assessed by receiver operating characteristic (ROC) curve analysis. RESULTS Posterior elevation of the thinnest point (TP), all positions of CTSP, PTI for all distances from the TP, and PVAK from a 5- to 7-mm distance from the TP were significantly different in the FFKC compared with the N group. The discriminant functions between the FFKC and the N groups and between the KC and the N groups reached an area under the ROC curve of 0.98 and 0.99, respectively. PTI indices and maximum posterior central elevation were the most important contributors to the discriminant function. CONCLUSIONS Indices generated from corneal thickness and curvature measurements over the entire cornea centered on the TP can identify very mild forms of ectasia undetected by a Placido-based neural network program.

Biomechanical Properties of Keratoconus Suspect Eyes

PURPOSE Measuring corneal biomechanical properties may help detect keratoconus suspect corneas and eliminate the risk of ectasia after LASIK. METHODS Data of 504 eyes separated into three groups were retrospectively reviewed: normal (n = 252), keratoconus suspect (n = 80), and keratoconus (n = 172). Corneal hysteresis (CH) and corneal resistance factor (CRF) were measured with an ocular biomechanics analyzer. RESULTS Mean corneal hysteresis was 10.6 +/- 1.4 (SD) mm Hg in the normal group, compared with 10.0 +/- 1.6 mm Hg in the keratoconus suspect group and 8.1 +/- 1.4 mm Hg in the keratoconus group. The mean CRF was 10.6 +/- 1.6 mm Hg in the normal group compared with 9.7 +/- 1.7 in the keratoconus suspect group and 7.1 +/- 1.6 mm Hg in the keratoconus group. Mean CH and CRF were significantly different between the three groups (P < 0.001). CONCLUSIONS CH and CRF alone cannot be used to identify keratoconus suspect corneas. Analyzing signal curves obtained with the biomechanics analyzer may provide additional valuable information for selecting qualified patients for refractive surgery.

Repeatability of measurements with a double-pass system.

PURPOSE: To evaluate the repeatability of measurements with a double‐pass system. SETTING: Rothschild Foundation, Paris, France. METHODS: Eyes were separated into 2 control groups (<30 years old and >40 years), a post‐refractive surgery group, and a cataract group. Measurements were performed using the Optical Quality Analysis System. The main outcome measures were the objective scattering index (OSI), the cutoff frequency of the modulation transfer function (MTF), and the Strehl ratio. The repeatability limit was obtained from the individual standard deviations. RESULTS: Forty‐two eyes were evaluated. The mean OSI value was 0.47 ± 0.11 (SD) in the younger control group, 1.73 ± 0.26 in the older control group, 1.34 ± 0.16 in the post‐refractive surgery group, and 6.15 ± 0.50 in the cataract group. The mean cutoff MTF value was 39.44 ± 3.93 cycles per degree (cpd), 26.07 ± 3.89 cpd, 28.34 ± 2.84 cpd, and 13.3 ± 1.69 cpd, respectively, and the mean Strehl ratio, 0.234 ± 0.023, 0.146 ± 0.021, 0.169 ± 0.023, and 0.098 ± 0.010, respectively. The repeatability limit for the whole population was 0.841 (33.5%) for the OSI, 8.499 (31.1%) for the cutoff MTF, and 0.051 (31%) for the Strehl ratio. CONCLUSIONS: The repeatability limit was good and equivalent for the OSI, the MTF, and the Strehl ratio values. There was a wide interval between the normal and pathologic threshold for OSI measurements, indicating that the reliability of the double‐pass device complies with the requirements for quantitative assessment of scattering. Financial Disclosure: No author has a financial or proprietary interest in any material or method mentioned.

Assessment of corneal biomechanical properties in normal tension glaucoma and comparison with open-angle glaucoma, ocular hypertension, and normal eyes.

Purpose:To assess the biomechanical properties of corneas in patients with normal tension glaucoma (NTG) and to compare them with those of patients with primary open-angle glaucoma (POAG), ocular hypertension (OHT), and normal controls (N). Methods:Corneal hysteresis (CH), corneal resistance factor (CRF), Goldmann intraocular pressure (IOPg), and corneal compensated IOP (IOPcc) were obtained using an ocular response analyzer for 28 eyes in 14 patients with NTG, 75 eyes in 38 patients with chronic POAG, 53 eyes of 27 patients with OHT, and 44 eyes of 22 N controls. IOP using Goldmann applanation tonometry (IOPGA) and ultrasonic central corneal thickness (CCT) were also measured for each eye. Analysis of variance test was used for statistical analysis. Results:CH was significantly lower in the NTG group (9.88±2.02 mm Hg) compared with the N group (11.05±1.53 mm Hg; P<0.01). CRF was significantly lower in the NTG group (9.5±1.89 mm Hg) compared with the POAG group (11.15±2.35 mm Hg; P<0.01) and to the N group (11.00±1.75 mm Hg; P<0.01). CCT was not considered significantly different between the 4 groups. However, IOPcc was found to be significantly lower in NTG group compared with the POAG group and OHT group (P<0.001). Conclusion:NTG was associated with significantly lower CRF than chronic POAG and N patients. CH and CRF could be a useful tool in early diagnosis of NTG.

Corneal thickness, curvature, and elevation readings in normal corneas: Combined Placido–Scheimpflug system versus combined Placido–scanning-slit system

PURPOSE: To evaluate agreement in central corneal thickness (CCT), keratometry, and anterior and posterior elevation map measurements in normal corneas between a combined Placido–Scheimpflug system and a combined Placido–scanning‐slit elevation topography system. SETTING: Department of Cataract & Refractive Surgery, Rothschild Foundation, Paris, France. DESIGN: Evaluation of diagnostic test or technology. METHODS: Measurements were performed with a combined Placido–Scheimpflug system (TMS‐5) and a combined Placido–scanning‐slit system (Orbscan II). Ultrasound (US) pachymetry was used as the reference for CCT measurements. Bland‐Altman plots were used to evaluate agreement between instruments. RESULTS: The mean CCT measurements by US pachymetry, the Placido–Scheimpflug system, and the Placido–scanning‐slit system were 556.74 μm ± 42.45 (SD), 543.23 ± 36.73 μm, and 564.45 ± 41.26 μm, respectively. Although the CCT readings were statistically significantly thinner with the Placido–Scheimpflug system than with the other systems, there was high correlation between instruments. Peripheral corneal thickness readings were also thinner with the Placido–Scheimpflug system than with the Placido–scanning‐slit system. Keratometry and anterior and posterior best‐fit sphere (BFS) measurements were comparable between the 2 optical devices. Anterior and posterior maximum central elevations measured by the 2 instruments were not comparable or strongly correlated. Repeatability after 3 successive measurements was excellent for all parameters except maximum central elevation. CONCLUSIONS: Although highly correlated, with corneal thickness readings were not interchangeable between the 2 optical devices. No statistically significant differences in keratometry or BFS measurements were observed between the 2 devices. There were important discrepancies in the maximum central elevation between the 2 topographers. Financial Disclosure: Drs. Gatinel and Saad are consultants to Technolas Perfect Vision. No other author has a financial or proprietary interest in any material or method mentioned.

Detection of static cyclotorsion and compensation for dynamic cyclotorsion in laser in situ keratomileusis

PURPOSE: To evaluate the degree of static and dynamic cyclotorsion using a rotational eye tracker in laser in situ keratomileusis (LASIK) to correct myopic astigmatism. SETTING: Rothschild Foundation, Paris, France. DESIGN: Cohort study. METHODS: Laser in situ keratomileusis with active iris registration using a Zyoptix 100 Hz excimer laser with Advanced Control Eyetracking was performed in eyes with myopic astigmatism. In all cases, iris registration was used to evaluate the degree of static cyclotorsion preoperatively and the degree of dynamic cyclotorsion and intraoperatively. The direction, mean values, and ranges of static and dynamic cyclotorsion were recorded. The amplitude of intraoperative cyclotorsion was reported. RESULTS: The study included 74 consecutive eyes (38 patients). The direction of cyclotorsion was not statistically significant. The mean static cyclotorsion was 3.08 degrees ± 2.68 (SD) (range −7.0 to 14.0 degrees) and the mean dynamic cyclotorsion, 3.39 ± 2.94 degrees (range −10.3 to 13.5 degrees). During photoablation, the mean amplitude of cyclotorsion was 2.69 ± 1.63 degrees (range 0.0 to 9.2 degrees). The magnitude of dynamic cyclotorsion was less than 5 degrees in 66% of eyes, 5 degrees or more in 34% of eyes, and 10 degrees or more in 4% of eyes. CONCLUSIONS: Static and dynamic cyclotorsion was detected with a dynamic eye tracker in eyes having LASIK. Rotational movements were mainly static but had significant amplitude during photoablation. Financial Disclosure: No author has a financial or proprietary interest in any material or method mentioned.

Intraoperative OCT-Assisted DMEK: 14 Consecutive Cases.

Purpose: To describe the utility of a new intraoperative optical coherence tomographer (OCT) to evaluate endothelio-Descemet graft orientation during Descemet membrane endothelial keratoplasty (DMEK) procedures. Methods: Prospective, observational, and single-center pilot case series including 14 eyes of 14 patients consecutively scheduled for DMEK surgery. After injecting the graft into the anterior chamber, the graft orientation was assessed with the help of anterior segment OCT. The surgical time and unfolding time were measured. The postoperative measurements included best-corrected visual acuity, central pachymetry, and specular microscopy at 1 month. Results: Using the OCT images, it was possible to evaluate the graft orientation in all cases. The mean unfolding time was 6.1 ± 3.0 minutes, the mean best-corrected visual acuity was 0.3 ± 0.3 logarithm of the minimum angle of resolution, the mean decrease in central pachymetry was 213 ± 177 &mgr;m, and the mean central endothelial cell count was 1906 ± 319 cells per square millimeter. Conclusions: Live intraoperative OCT is useful to visualize and assess graft orientation in DMEK surgery. It enables faster graft positioning with less graft manipulation in the presence of severe corneal edema.

Photorefractive keratectomy in patients with suspected keratoconus: Five-year follow-up

Purpose To assess the long‐range outcomes of photorefractive keratectomy (PRK) using functional and topographic criteria in myopic eyes with suspected keratoconus. Setting Rothschild Foundation, Paris, France. Design Retrospective interventional case series. Methods Eyes of patients classified as keratoconus suspects or keratoconus by the Corneal Navigator software of the OPD‐Scan II device were included. They were treated with myopic PRK using an EC‐5000 excimer laser between 2004 and 2007. The main outcome measures were refractive stability, mean corneal keratometry, mean central pachymetry, mean thinnest point value, and the occurrence of postoperative complications such as corneal ectasia. Results The study evaluated 62 eyes of 42 patients. The mean patient age was 34.6 years ± 15.1 (SD) and the mean spherical equivalent (SE), −3.96 ± 3.05 diopters (D). The mean central pachymetry was 529.4 ± 32.8 μm and the mean simulated keratometry, 45.75 ± 1.75 D. The percentage of similarity to keratoconus suspects or keratoconus was positive in all 62 eyes and exceeded a 50% similarity score in 30 eyes (48.4%). The mean follow‐up was 4.8 ± 1.4 years. The mean magnitude of the SE was −0.53 ± 1.35 D over the follow‐up. Two patients required glasses postoperatively because of significant myopic regression. No case of corneal ectasia was reported. Conclusion Photorefractive keratectomy in eyes with suspected keratoconus based on a Placido neural network may be safe and effective for myopia and astigmatism in carefully selected patients. Financial Disclosure No author has a financial or proprietary interest in any material or method mentioned.

Bilateral corneal ectasia after laser in situ keratomileusis in patient with isolated difference in central corneal thickness between eyes

A patient was treated bilaterally for myopia using laser in situ keratomileusis (LASIK). Preoperatively, there was no known risk factor for ectasia but a 20 microm between-eye difference in central mean corneal thickness was seen on the optical pachymetry map. Two years postoperatively, bilateral ectasia was diagnosed. This case suggests that abstention or surface ablation treatment may be a safer option than LASIK in patients showing central thickness asymmetry between eyes.

Recentration of a small-aperture corneal inlay

UNLABELLED We report 2 patients implanted with a small-aperture corneal inlay to correct presbyopia. After the surgery, both patients complained of visual symptoms and poor visual acuity. The distances from the center of the inlay to the corneal vertex center were 593 μm nasally and 159 μm superiorly in Case 1 and 72 μm temporally and 17 μm superiorly in Case 2. The 2 inlays were recentered at 2 weeks and 3 weeks postoperatively, resulting in significant improvement in the visual acuity and quality of vision. Accurate centration of a small-aperture corneal inlay seems to be an important factor in obtaining a satisfactory result. Recentration is possible and improves visual acuity if proper centration was not obtained after the first surgery. FINANCIAL DISCLOSURE Dr. Saad is a consultant to Acufocus, Inc. Dr. Gatinel is an investigator for a clinical trial conducted with the small-aperture inlay. He does not have any financial interest in relation to this inlay. Neither of the other authors has a financial or proprietary interest in any material or method mentioned.