OCT Biometry of the Crystalline Lens during Dynamic Accommodation

Abstract

Purpose : To quantify changes in crystalline lens thickness and radii of curvature during dynamic accommodation using extended depth OCT.

Methods : In-vivo responses to an accommodative step stimulus of three subjects (aged 22, 39, and 45) were captured using a custom-made extended-depth SD-OCT system operating at 840nm following an IRB-approved protocol. The OCT system produced images of the entire anterior segment from the anterior cornea to the posterior lens with a frame rate of 13Hz (Ruggeri et al, Biomed Opt Exp, 2012). During imaging, subjects focused on a visual accommodation target designed to produce an adjustable step stimulus of accommodation. Accommodative responses to a 2D and 4D stimulus were measured. Each image in the sequence was segmented using a custom-developed automated algorithm that exploits derivative and intensity image cues to localize the corneal and lens boundaries. The segmented corneal and lens contours were corrected for refractive distortions. Radius of curvature was determined by fitting the central 6mm of each distortion corrected contour with a conic curve. Values of lens thickness and curvature in the relaxed and accommodated states were calculated by averaging values before and after the stimulus was applied. The dynamic changes in lens thickness and curvature were fit with an exponential model to produce time dependent constants.

Results : Results are summarized in Table 1. Anterior lens radius decreased over time in all subjects. Posterior lens curvature experienced a slight increase in average curvature for all subjects. The time constant of lens thickness and lens curvature were similar.

Conclusions : This study demonstrates the feasibility of quantifying the dynamic changes in lens curvature and thickness during accommodation using extended-depth OCT combined with a step accommodation stimulus and an automated segmentation algorithm.

This is an abstract that was submitted for the 2016 ARVO Annual Meeting, held in Seattle, Wash., May 1-5, 2016.

 

Accommodative responses for 22yo subject. Graphs show radius of anterior lens (left), posterior lens (center) and lens thickness at the center of the pupil over time (right).