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E. Azan, A. Saad, D. Gatinel; Correlations Between Biomechanic and Topographic Corneal Parameters: Normal versus Keratoconus. Invest. Ophthalmol. Vis. Sci. 2010;51(13):4625.
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Correlations between biomechanical and topographic parameters: normal versus keratoconus
Measuring the corneal biomechanical properties and knowing about the correlations between biomechanical and topographic parameters for normal and keratoconus corneas.
Retrospective comparative observational non-interventional study of a case series. We reviewed data of 217 eyes separated into two groups: normal (n=90), keratoconus (n=127). The Corneal Hysteresis (CH) and Corneal Resistance Factor (CRF) were measured by the Ocular Response Analyzer (ORA, Reichert, Inc., Buffalo, NY USA) Segregation of the two groups was based on the results of the Nidek OPD scan videokeratograph (Nidek CO., LTD, Gamagori, Japan). The Nidek Corneal Navigator (NCN) uses an artificial intelligence technique to train a computer neural network to recognize specific classifications of corneal topography. Eyes in the normal group had a score of 99% similarity to normality using the NCN analysis. In addition, data provided by the Orbscan II (Bausch & Lomb, NY) for the normal group did not reveal topography patterns suggestive of forme fruste keratoconus such central keratometry greater than 47.0 diopters (D).The keratoconus group included eyes that had frank keratoconus diagnosed by an experienced corneal specialist.The following information was obtained for each patient: age, sex, and data related to the ORA: CH, CRF, and the difference between CH and CRF. Central corneal thickness (CCT) was provided by optical pachymetry. Also, data on the keratometry in the 3, 5 and 7 mm was provided, with the 25 Placido derived indices from the OPD (surface asymmetry, keratometry in various zones, etc...)All numerical results were entered into a database and statistical analyses were performed with XLSTAT2006 (Addinsoft) using ANOVA. A p value less than 0.05 was considered statistically significant.Results :There were significantly more males in the keratoconus group (p<0.001). The mean age was not statistically different between the two groups. Mild correlations were found for some parameters. The higher correlation was found between the difference (CH-CRF) and the keratometric value of the steepest meridian in the central 3 mm for both groups. This correlation was higher in the keratoconus group R=0,483 (P<0,001) than in the normal group R=0.442 (P<0,001).Conclusion :This is the first study to compare the correlations between biomechanical and topographic properties for normal and keratoconus. Knowing more about these correlations may help to better understand the consequences of topographic parameters on the corneal biomechanical parameters.
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