Quantification of ciliary muscle thickness changes during accommodation from dynamic transscleral OCT images

Abstract

Purpose : Recent studies have demonstrated the ability of OCT to quantify changes in ciliary muscle thickness with age and accommodation, giving insight into the potential role of the ciliary muscle in presbyopia. Prior studies have relied on measurements acquired statically at fixed accommodative demands. The purpose of this study is to quantify the dynamics of the ciliary muscle thickness changes during accommodation.

Methods : Following an approved protocol, transscleral images of the ciliary muscle of the left eye of 23 subjects (range: 16 to 71 y/o) with spherical equivalent refractive errors ranging from -7.5 to +1 D were acquired at 13 Hz during a response to a 2D accommodative step stimulus. A Spectral-Domain OCT system (1320nm, 28,000 A-lines/s, 7.5 µm axial resolution, and 2.5 mm axial range, Thorlabs Telesto, Newton, NJ) coupled with a custom accommodation module (Ruggeri et al, Biomed Opt Exp, 2016: 1351-1364) was used. For each subject, we acquired a series of 160 B-scans containing 897 A-lines. A MATLAB program was developed to measure the ciliary muscle thickness in each frame. Thickness was measured in the vicinity of the middle part of the muscle where the muscle boundaries could be clearly identified. The change in the muscle thickness was calculated as the difference between the average thickness obtained from the first 10 frames (unaccommodated state) and that obtained from the last 10 frames (accommodated state) of the dynamic recording. The relations between the change in thickness of the ciliary muscle and age as well as refractive error were quantified.

Results : Ciliary muscle thickness in the relaxed state was not found to be dependent on age (p=0.951) but was dependent on refractive error (p<0.001). The average of the ciliary muscle thickness change during accommodation of all other subjects was 0.062+/-0.074mm. There was not a statistically significant dependence on age (p-value > 0.005). The change in ciliary muscle thickness decreased with increasing myopia (p-value < 0.001).

Conclusions : Ciliary muscle thickness changes with accommodation were found to be independent of age but dependent on refractive error.

This abstract was presented at the 2022 ARVO Annual Meeting, held in Denver, CO, May 1-4, 2022, and virtually.

 

Typical ciliary muscle image (top) and the dynamic thickness changes (bottom) (age = 16 years). Thickness was measured where both boundaries could be clearly detected (white crosses).

 

Ciliary muscle thickness change as a function of age and refractive error.