Assessment of scleral shape and thickness during accommodation using OCT

Abstract

Purpose : Recent studies have shown that scleral shape may change during accommodation, suggesting these changes could influence the accommodative response. The purpose of this study was to investigate if accommodation induces any changes in the shape and thickness of the sclera using OCT.

Methods : We used an SD-OCT system combined with an accommodation target (Ruggeri et al, Biomed Opt Express 7: 1351-1364; 2016) to image the conjunctiva-sclera complex dynamically during accommodation. The temporal side of the left eye of five subjects (22, 23, 33, 34 and 39 years old) with spherical equivalent refraction between -4 and 0 D was imaged in response to a stimulus stepping from 0 to 4 D. Eighty OCT images were sequentially acquired at a rate of 13 frames per second while the subject responded to the step stimulus. Spatial registration of each OCT sequence was performed to minimize motion artifacts. Each OCT image was segmented and corrected for distortion (Figure - A). Thickness of the conjunctiva-sclera complex was calculated at the scleral spur and moving posteriorly at 1, 2, 3 and 4 mm along the conjunctival surface (TKN_0,1,2,3,4). At each position, the average thickness of the first 10 images (relaxed state) and the last 10 images (accommodated state) of the dynamic imaging session was calculated. For each subject, the average contour of the conjunctival surface of the first 10 images (relaxed state) and the last 10 images (accommodated state) was calculated (Figure – B). Maximum (D_MAX) and root mean squared (D_RMS) difference between the relaxed and accommodated mean conjunctiva contours were calculated to quantify the change in shape of the conjunctiva-sclera complex.

Results : A repeated measures ANOVA showed no changes (p = 0.71) in mean thickness (ΔTKN) with accommodation. We also found no consistent change in D_MAX (p = 0.52) across subjects, with accommodation (Table). The mean change in thickness (ΔTKN) was less than 6 µm in all positions. D_MAX and D_RMS were less than 13 and 8 µm, respectively. All changes were comparable to the pixel size of the images (5 µm axial × 11 µm transversal).

Conclusions : The thickness and shape of the conjunctiva-sclera complex did not change significantly during accommodation. The results suggest that the sclera does not deform during accommodation.

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