An analysis of anterior scleral shape and its role in the design and fitting of scleral contact lenses.

Abstract

The purpose of this study was to evaluate the shape of the anterior sclera by measuring the sagittal height and corneoscleral transition angles in the four cardinal and four oblique segments of the eye. In this study, 78 normal eyes of 39 subjects were evaluated. The sagittal height, corneoscleral angle and scleral angle were measured at three chord lengths (10.0mm, 12.8mm and 15.0mm) in all eight segments of the anterior eye using optical coherence tomography (Zeiss Visante AS-OCT). Scleral toricity was calculated for each eye, defined as the greatest sagittal height difference found between two perpendicular meridians. At a 12.8mm chord length, the shape of the anterior eye was found to be nearly rotationally symmetric, and at a chord of 15.0mm the shape became more asymmetric. The average sagittal heights of the eight segments at a 12.8mm chord ranged from 2890μm to 2940μm; at a 15.0mm chord they ranged from 3680μm to 3790μm. The average scleral angles at a 15.0mm chord ranged from 35.17° to 38.82°. Significant differences between opposing segments were found in the sagittal height and scleral angle measurements at a chord of 15.0mm (sagittal height p≤0.0021; scleral angle p≤0.0105). The nasal measurements revealed flatter scleral angles and concave corneoscleral transitions, whereas temporal scleral angles were steeper, with tangential or convex corneoscleral transitions. These findings are important to consider when designing and fitting contact lenses that rest beyond the boundaries of the limbus, such as scleral lenses.