title: Corneal-thickness spatial profile and corneal-volume distribution: tomographic indices to detect keratoconus.
abstract: OBJECTIVE
  To evaluate whether the corneal-thickness spatial profile and corneal-volume distribution differentiate keratoconic corneas from normal corneas using new tomography parameters.
  
  
  METHODS
  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.
authors.affiliation: Instituto de Olhos Renato Ambrósio, Rio de Janeiro, Brazil. renatoambrosiojr@terra.com.br
authors.forename: Renato
authors.initials: R
authors.lastname: Ambrósio
authors.forename: Ruiz Simonato
authors.initials: RS
authors.lastname: Alonso
authors.forename: Allan
authors.initials: A
authors.lastname: Luz
authors.forename: Luis Guillermo
authors.initials: LG
authors.lastname: Coca Velarde
mesh_terms: D003315:Cornea / Q000473:pathology*; D003941:Diagnostic Techniques, Ophthalmological; D005260:Female; D006801:Humans; D021621:Imaging, Three-Dimensional / Q000379:methods*; D007640:Keratoconus / Q000175:diagnosis*; D008297:Male; D014054:Tomography / Q000379:methods