A Quantitative Method for the Analysis of Bilateral Corneal Asymmetry in Different Corneal Categories

Abstract

Purpose It is generally accepted that the presence of bilateral corneal asymmetry correlates with certain corneal diseases and may be the evidence of corneal abnormalities. A method is shown for the quantification of bilateral corneal asymmetry in 5 different corneal categories, making use of corneal topography data. Methods Corneal topographies (Tomey TMS, Nagoya, Japan) from both eyes of 74 subjects were reviewed by a cornea researcher who classified them according to their characteristics into five groups (normal, astigmatic, contact-lens-induced corneal warpage, keratoconus suspects and bilateral keratoconus). Topography maps were chosen from the clinical records of the LSU Eye Center. The axial-diopters tables for each pair of corneas were extracted from their corresponding corneal topographies. The resulting data from the corneal topographies of each eye were interpolated at regular intervals using a polar-coordinate system. Subsequently, the differences between corresponding points of the axial-diopters tables of the fellow eyes were calculated. The cumulative percentage of the resulting values was calculated and its distribution was plotted for each pair of eyes. A linear regression was fitted to the data of each cumulative distribution plot. Finally, the slope of the linear regression of each pair of eyes was calculated and statistical analysis was performed in order to determine whether or not there is a statistically significant difference between the slopes of each group of corneal categories. Results A statistically significant difference ( P<0.05) was found between keratoconus and all the other groups. Furthermore, we found a statistically significant difference between the normal and the contact-lens-induced warpage group as well as between the normal and the keratoconus-suspects group ( P<0.05). There was no statistically significant difference ( P>0.05) neither between the normal and the astigmatism group, nor between the astigmatism and the contact-lens-induced corneal warpage group, nor between the astigmatism and the keratoconus-suspects group, nor between the keratoconus-suspects group and the contact-lens-induced corneal warpage one. Conclusions A method to quantify bilateral corneal asymmetry in different corneal entities was devised. The lowest degree of bilateral asymmetry was observed in the normal group, while the highest degree of bilateral asymmetry was obtained for the keratoconus group. The contact-lens-induced warpage group and the keratoconus-suspects group presented with intermediate bilateral asymmetry.