Topographical differences in the sclera of myopes and emmetropes

Abstract

Purpose : To investigate differences in scleral shape between myopes and emmetropes.

Methods : Three-dimensional (3D) maps from both eyes of 25 subjects (26 ± 6 y.o.) were acquired using a corneo-scleral topographer (Eye Surface Profiler). Thirteen participants were categorised as emmetropes (refractive error (RE) between -0.25 D and +0.50 D) and twelve participants were categorised as myopes (RE < -0.75 D). The refractive state was measured monocularly using a wide-view open window autorefractometer. 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 a 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. In addition, for each participant the area under the curve of the elevation difference between the original and fit data was calculated and correlated with refractive power.

Results : Scleral asymmetry magnitude is larger in emmetropes than myopes (p < 0.05/N (Bonferroni)), as shown in the Figure. In addition, scleral asymmetry was found to decrease with refractive power (R²=0.55, p<<0.001), and higher refractive errors correspond with less scleral asymmetry. Very strong positive correlations between right and left eye were found (Spearman ρ = 1.000; p < 0.001) for both groups.

Conclusions : In the effort to better understand how myopia develops, we have demonstrated that there is a significant difference in scleral shape between myopes and emmetropes. This difference is correlated with refractive power, with more myopic eye having more regular scleras. This may be the result of increased stretching forces in myopes compared to emmetropes.

This is an abstract that was submitted for the 2018 ARVO Annual Meeting, held in Honolulu, Hawaii, April 29 - May 3, 2018.

 

Figure. Scleral elevation profile over 360 degrees for a scleral ring with a radius of 6-8 mm in a left emmetropic eye (RE = 0.25 D) and a left myopic eye (RE = –5.75 D). Right eyes were corrected for mirror symmetry.