Corneal-thickness spatial profile and corneal-volume distribution: Tomographic indices to detect keratoconus
Accepted 18 June 2006.
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.
From Instituto de Olhos Renato Ambrósio (Ambrósio Alonso) and Fluminense Federal University (Ambrósio, Alonso, Coca Velarde), Rio de Janeiro, and Altino Ventura Foundation (Luz), Recife, Brazil
Corresponding author: Renato Ambrósio Jr, MD, PhD, Rua Conde de Bonfim 211/712, Tijuca, Rio de Janeiro-RJ, 20520-050. Brazil.
Dr. Ambrósio is a consultant to Oculus-Optikgeräte GmbH. No other author has a financial or proprietary interest in any material or method mentioned.
ABSTRACT