Mean shape of the human limbus.

Purpose: To characterize the mean topographic shape of the limbus of a normal human eye and determine whether it depends on age or refractive power.

Setting: University of Manchester, Manchester, United Kingdom.

Design: Prospective case series.

Methods: Participants with no previous ocular surgeries were included in this study. The left eye was measured with a corneoscleral topographer (Eye Surface Profiler). From the raw anterior eye height data, the topographic limbus was demarcated and fitted in 3 dimensions to a circle, an ellipse, and a Fourier series. The root mean square error was calculated to evaluate the goodness of fit. In addition, the white-to-white (WTW) corneal diameter was taken from the readings of the measuring device. For statistical analysis, participants were grouped according to their age and their spherical equivalent correction.

Results: The study comprised 74 participants aged 20 to 84 years. From the considered models, the 2nd-order Fourier series was the most accurate model to describe the shape of the human limbus. The mean difference between the topographic limbus diameter and the WTW corneal diameter was 0.33 mm ± 0.24 (SD). There were statistically significant differences between eye quadrants (P < .001); however, there were no statistically significant differences in the horizontal and vertical meridians between age groups (P = .71 and P = .082, respectively) or between eyes with myopia and eyes with emmetropia (P = .78 and P = .68, respectively).

Conclusion: The human limbus is not symmetrical and although its shape is person-dependent, it is not related to age or the eye's refractive power.