Ruiz Simonato Alonso

Corneal-thickness spatial profile and corneal-volume distribution: Tomographic indices to detect keratoconus

PURPOSE: To evaluate whether the corneal‐thickness spatial profile and corneal‐volume distribution differentiate keratoconic corneas from normal corneas using new tomography parameters. SETTING: Subspecialty cornea and refractive practice, Fluminense Federal University, Rio de Janeiro, Brazil. METHODS: Forty‐six eyes diagnosed with mild to moderate keratoconus and 364 normal eyes were studied by the Pentacam Comprehensive Eye Scanner. Corneal thickness at the thinnest point and the averages of the points on 22 imaginary circles centered on the thinnest point with increased diameters at 0.4 mm steps were calculated to create a corneal‐thickness spatial profile. Corneal volume was calculated within diameters from 1.0 to 7.0 mm with 0.5 mm steps centered on the thinnest point to create the corneal‐volume distribution. The percentage increase in thickness and the percentage increase in volume were calculated for each position of the corneal‐thickness spatial profile and corneal‐volume distribution from their first value. Statistical analysis was done using the Wilcoxon 2‐independent‐sample test to compare mean levels using S‐Plus‐4.0 software (MathSoft) and a normal linear model under a Bayesian frame for estimating the mean variation in thickness and volume using the BUGS 0.6 package. RESULTS: Statistically significant differences were observed between the groups (P<.05) in all positions of corneal‐thickness spatial profile and corneal‐volume distribution and in the percentage increase in thickness and percentage increase in volume between 3.5 mm and 7.0 mm diameters. CONCLUSIONS: Corneal‐thickness spatial profile, corneal‐volume distribution, percentage increase in thickness, and percentage increase in volume were different between keratoconic corneas and normal corneas and could serve as indices to diagnose keratoconus and screen refractive candidates. Further studies are necessary to evaluate whether these tomographic indices are more sensitive and specific than the classic Placido‐based topography.

Glaucoma anterior chamber morphometry based on optical Scheimpflug images

PURPOSE To compare the performance of gonioscopy and noncontact morphometry with anterior chamber tomography (High Resolution Pentacam - HR) using optical Scheimpflug images in the evaluation of the anterior chamber angle (ACA). METHODS Transversal study. 112 eyes from 74 subjects evaluated at the Glaucoma Department, Fluminense Federal University, underwent gonioscopy and Pentacam HR. Using gonioscopy, the ACA was graded using the Shaffer Classification (SC) by a single experienced examiner masked to the Pentacam HR findings. Narrow angle was determined in eyes in which the posterior trabecular meshwork could not be seen in two or more quadrants on non-indentation gonioscopy (SC Grade 2 or less). Pentacam HR images of the nasal and temporal quadrants were evaluated by custom software to automatically obtain anterior chamber measurements, such as: anterior chamber angle (ACA), anterior chamber volume (ACV) and anterior chamber depth (ACD). RESULTS Based on gonioscopy results, 74 (60.07%) eyes of patients classified as open-angle (SC 3 and 4) and 38 (33.93%) eyes of patients classified as narrow-angle (SC 1 and 2). Noncontact morphometry with Scheimpflug images revealed a mean ACA of 39.20 ± 5.31 degrees for open-angle and 21.18 ± 7.98 degrees for narrow-angle. The open-angle group showed significant greater ACV and ACD values when compared to narrow-angle group (ACV of 193 ± 36 mm³ vs. 90 ± 25 mm³, respectively, p<0.001; and ACD of 3,09 ± 0,42 mm vs. 1,55 ± 0,64 mm, respectively, p<0.0001.). In screening eyes with open-angle and narrow-angle with the Pentacam ACA of 20º (SC Grade 2) using the ROC curves, the analysis showed 52.6% of sensitivity and 100% of specificity. CONCLUSIONS The Pentacam showed ability in detecting eyes at risk for angle closure analyzing ACV and ACD.

Repeatability of central corneal thickness measurement with the Pentacam HR system

PURPOSE: To assess the repeatability of central corneal thickness measurement at the geometrical center (Central Corneal Thickness - CCT) given by the Pentacam High Resolution (HR) Comprehensive Eye Scanner (Oculus, Wetzlar, Germany) over time. METHODS: Prospective, single center, observational study. Two separate CCT measurements were taken by the Pentacam corneal tomography exam (CTm) 3 to 12 months apart, and compared. RESULTS: One hundred and sixteen eyes (n=116) of 62 health patients were included in this study. Average CCT in first and last visits was 541.6±37 µm and 543.6±36.9 µm respectively. Mean difference between both measurements was 9.2±6.4 µm, and there was no statistically significant difference in CCT measurement between visits, with good correlation between them (P = 0.057, r2 = 0,9209). CONCLUSION: Pentacam (HR) CTm gives repeatable CCT measurements over time.