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Intraocular pressure and biomechanical corneal properties in normal and keratoconic eyes with CorVis ST and ORA

Session Details

Session Title: Corneal biomechanics

Session Date/Time: Tuesday 08/10/2013 | 08:00-10:30

Paper Time: 09:42

Venue: Elicium 1 (First Floor)

First Author: : J.Salgado-Borges PORTUGAL

Co Author(s): :    F. Esteves   F. Rodrigues   P. Neves   R. Leitćo   I. Lopes-Cardoso   J.

Abstract Details


To evaluate the differences in intra-ocular pressure and biomechanical properties of the cornea measured with Corvis ST and Ocular Response Analyzer in a population of keratoconus patients and a control population of young healthy patients.


Department of Ophthalmology - CHEDV, Santa Maria da Feira - Portugal and CEORLab - Center of Physics - University of Minho – Braga - Portugal


Eighty right eyes from 80 young healthy patients (60 females, 20 males; age=25±5 years) and ninety-one eyes from 47 non-operated keratoconus patients (21 females, 26 males; age=37±12 years) were included in the study. All patients were evaluated with Ocular Response Analyzer (ORA, Reichert, Depew, NY) and Corvis ST (Oculus, Wetzlar, Germany) in random order in the same session. Differences between groups for IOP, central corneal thickness (CCT) as well as the biomechanical parameters were obtained as well as correlations between biomechanical properties with both instruments and IOP obtained and CCT provided by the Corvis ST separately for normal eyes and keratoconus eyes.


IOP was significantly lower (p<0.001) in keratoconus (13.0±2.5 mmHg) than normal eyes (15.1±1.7 mmHg) as was CCT being 476±57 microns for keratoconus compared to 527±31 microns for normal eyes (p<0.001). Corneal compensated IOP (IOPcc) measured with ORA was significantly higher in the keratoconus group (p<0.001) while Goldmann equivalent IOP (IOPg) were not significantly different (p=0.169). Corneal resistance factor (CRF) and corneal histeresys were significantly lower in keratoconus compared to normal eyes (p<0.001). Highest concavity peak distance (5.0±0.2 vs 4.8±0.9 mm for normal and keratoconus, p=0.016), deformation amplitude (1.1±0.1 vs 1.1±0.2 mm for normal and keratoconus, p<0.001) and radius (7.1±0.7 vs 6.1±1.2 mm for normal and keratoconus, p<0.001) were significantly different between groups. In normal eyes, several Corvis ST biomechanical parameters were correlated with IOP and CCT provided by Corvis ST including time for applanation 1 and 2, velocity for applanation 2 as well as highest concavity peak distance, radius and deformation amplitude (Pearson correlation coefficient between 0.600 and 0.990; p<0.001). The same parameters were significantly correlated with CCT provided by Corvis ST but to a lower extent (Pearson correlation coefficient between 0.239 and 0.563; p<0.001).


Corvis ST provides several parameters that differentiate keratoconic from normal eyes. Correlation between these parameters and IOP and CCT measured with Corvis ST are slightly different in normal and keratoconic eyes with CCT having a larger weight in the biomechanical behavior of the cornea in keratoconus.

Financial Interest:


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