Mean shape of the human sclera

Purpose To assess the mean shape of the human sclera Methods Three‐dimensional (3D) maps from the left eye of 27 subjects (26 ± 6 y.o.) were acquired using a corneo‐scleral topographer (Eye Surface Profiler). Subjects were asked to open their eyes wide to ensure 360 degrees scleral coverage. For each 3D map, the sclera (maximum diameter 16 mm) and cornea were automatically separated at the level of the limbus, assuming a mean limbal diameter of 12 mm based on recent work. The remaining 3D scleral ring was further fit to a quadratic function, chosen arbitrarily to account for the bulk of surface data. The elevation difference between the original and fit data was calculated. For statistical analysis, sclera was separated in four disjoint quadrants, superior [60,120]˚, inferior [240,300]˚, nasal [150,210]˚ and temporal [330,30]˚. Results Along the horizontal meridian, the temporal aspect of the sclera showed less elevation (mean ± SD : −240 ± 90  μ m) than the nasal aspect (−60 ± 20  μ m), being statistically significant different (paired t‐test, P  << 0.001). Along the vertical meridian, the inferior aspect of the sclera (−60 ± 110  μ m) showed to be less elevated than the superior aspect (50 ± 100  μ m), being statistically significant different (paired t‐test, P  = 0.002). Conclusions The sclera is circularly asymmetric. The nasal sclera is higher/flatter, and the temporal sclera is lower/steeper. The insertion of the eye muscles on the eyeball could justify these differences. Scleral shape affects all contact lens designs that interact with the corneo‐scleral junction and beyond. Thus, these findings have an important potential impact on contact lens fit.