Anterior scleral changes with accommodation and convergence

Abstract

Purpose: Recent research investigating ocular changes associated with near tasks indicates accommodation may affect the anterior scleral shape. This study aimed to examine the effects of accommodation, convergence and their interaction upon anterior scleral shape. Methods: The right eyes of 36 young healthy adult subjects (mean age 23.5 ± 3.8 years) had measures of anterior eye shape collected with the Eye Surface Profilometer (ESP) before and during visual tasks under three conditions: 5 D accommodation (0° convergence), 9° convergence (0 D accommodation), and a combination of 5 D accommodation and 9° convergence. Accommodative stimuli were introduced using a Badal optometer via a beam splitter. Three ESP scans were captured and the sagittal height data were averaged along a horizontal cross-section in 0.7 mm width zones in both the peripheral cornea and the anterior sclera (Figure 1). Results: The anterior scleral surface exhibited a small anterior movement (mean height change of 5 ± 2 µm, p = 0.04) in the zone up to 0.7 mm beyond the nasal limbus during accommodation. Greater movement occurred during convergence in the zone up to 0.7 mm and in the zone 0.7 to 1.4 mm beyond the nasal limbus (mean changes 13 ± 4 and 19 ± 6 µm, respectively, both p < 0.01) (Figure 2), and similar movement (10 ± 4 µm and 15 ± 5, both p < 0.02) occurred in the same nasal scleral zones during the combined convergence and accommodation condition. No significant changes in temporal anterior surface height were observed for any condition. Conclusions: Accommodation and convergence produce small but significant changes to anterior surface shape in the nasal anterior scleral region. The largest changes occurred during convergence, and this is most likely due to medial rectus contraction.