Eyelid pressure: inferences from corneal topographic changes

Abstract

Purpose: It is known that eyelid pressure can influence the corneal surface. However the distribution of eyelid pressure, the eyelid contact area and the biomechanics of the changes are unknown. While these factors are difficult to directly measure, analysis of eyelid-induced corneal topography changes and eyelid morphometry enable some inferences to be drawn. Methods: Eighteen subjects, aged between 19 and 29 years, with normal ocular health were recruited. Corneal topography changes were measured after four conditions consisting of two downward gaze angles (20° and 40°) and two types of visual tasks (reading and steady fixation). Digital photography recorded the width of Marx’s line, the assumed region of primary eyelid contact with the cornea. Results: Significantly larger corneal changes were found after the 40° downward gaze conditions compared with 20° due to the upper eyelid contact (p<0.001). For the 40° downward gaze tasks, the lower eyelid changes were greater than those due to the upper eyelid (p<0.01). The upper eyelid Marx's line width was associated with the amplitude of corneal change (R²=0.32, p<0.05). Conclusion: Analysis of the corneal topography changes gives insight into the pressure applied by the upper and lower eyelids in different situations. These include greater upper eyelid pressure with increasing downward gaze and larger lower eyelid pressure compared to the upper eyelid in 40° downward gaze. There was some evidence that supports Marx’s line as the primary site of contact between the eyelid margins and the cornea.