The evaluation of normal corneal topography in emmetropic eyes with computer-assisted videokeratography

By defining the topographic features of normal corneas, corneal surface abnormalities and their relation to visual function may be better understood. In our study, we have defined the corneal topographic features of emmetropic eyes to evaluate the relationship between topographic patterns and visual acuity.

Topographic pattern of 114 normal corneas of 114 emmetropic subjects with a keratometric astigmatism of 0.5 D or less were analyzed by computer-assisted videokeratography. Thetopographic maps were grouped into the following patterns: round, oval, symmetric bow tie, asymmetric bow tie, and irregular.

Asymmetric bow tie was the most common topographic pattern in our study population (33%), followed by symmetric bow tie (29%), round (14%), irregular (12%), and oval (11%) patterns. There were significant differences in the astigmatic values obtained by keratometry versus videokeratography for aspheric patterns, while the values among the spheric patterns were more in agreement. Mean corneal astigmatism calculated from videokeratographic data was 0.24 D for round, 0.61 D for oval, 1.05 D for symmetric bow tie, 0.85 D for asymmetric bow tie, and 0.76 D for irregular patterns.

We conclude that: the topographic configuration may not be a good predictor of visual function; an emmetropic eye may have an aspheric topographic pattern, such as asymmetric or symmetric bow tie; and the reconstruction algorithm used for providing topographic maps may not be accurate enough to determine the true shape of the corneal surface for interpretation.