Abstract
Purpose :
The accommodative response of the ciliary muscle (CM) is usually quantified from transscleral OCT images using thickness profiles. This approach does not capture the inward movement and change in length of the CM which is observed in real-time ultrasound images. We present a method to quantify the CM movement from transscleral OCT images acquired dynamically during accommodation.
Methods :
A transscleral SD-OCT system operating at 1325 nm (Ruggeri et al, Biomed Opt Exp; 2016) was used to acquire OCT image sequences of the CM through the temporal side of the left eye of 3 young subjects (ages: 22, 25, 26 years) and two pre-presbyopic subjects (age: 45 years) during accommodation. The system is combined with an accommodation target to produce a monocular accommodation step stimulus during imaging. Each recording consisted of a sequence of 160 OCT images acquired over 6.2 seconds. The dynamic response of the CM was recorded in response to step stimuli of 2D and 4D for the young subjects, and 2D for the pre-presbyopic subjects. The system is synchronized with an extended depth SD-OCT system that simultaneously acquires images of the crystalline lens during accommodation (Ruggeri et al, Biomed Opt Exp; 2016). In-house software was used to segment the ciliary muscle and lens boundaries in each image. Procrustes analysis was used to register the sequences of CM images assuming that there is no change in CM volume during accommodation. The movement of the CM centroid and apex were then quantified. Changes in lens thickness were also assessed to confirm that all subjects accommodated.
Results :
For a 2D stimuli, the change in lens thickness with accommodation ranges from 0.09 to 0.13 mm in the young subjects, and from 0.07 to 0.09 mm in the pre-prebyopic subjects. For a 4D stimulus, the change in lens thickness ranges from 0.13 to 0.20 mm in the young subjects. Figure A shows the change in contour of the ciliary muscle of a young subject (22 y/o) responding to a 4D stimulus. Figures B-F show the dynamic response of the position of the CM apex (left) and the time course of the change in the CM apex position and lens thickness (right) during accommodation.
Conclusions :
We demonstrated the feasibility of quantifying the dynamics of the ciliary muscle movement from transscleral OCT images. The results show that the contraction of the cilary muscle in young and pre-presbyopic subjects is comparable.
This abstract was presented at the 2022 ARVO Annual Meeting, held in Denver, CO, May 1-4, 2022, and virtually.