High-speed imaging and biometry of human accommodation dynamics with SS-OCT

Abstract

Purpose : Information on crystalline lens dynamics is needed to enable the design of approaches to restore accommodation. Recent studies (Labhishetty et al, J Optom 2019;12:22-29) suggest that high sampling rates are needed to obtain reliable measurements of accommodation dynamics. The purpose of this study was to develop a SS-OCT system for high-speed imaging and biometry of the anterior segment during accommodation.

Methods : A SS-OCT system was developed to measure intraocular distances and surface shapes of the anterior segment at high speed during accommodation. The system employs a spectrally balanced interferometer and a swept laser (Axsun Tech., Inc.) with 1310 nm central wavelength, 125 nm tuning range and 100 kHz sweep rate. The OCT signal is detected with a dual balanced receiver (1 GHz bandwidth; Thorlabs, Inc.) and digitized (14-bit, 2 GS/s; Acqiris, SA). The system provides an axial resolution of ~13 µm (in air) and a maximum axial range of 34.8mm. The OCT delivery probe was coupled to an accommodation target (Ruggeri et al, Biomed Opt Express 2012;7:1506-20) that provides monocular accommodation step stimuli to allow imaging during accommodation. The response to a stimulus stepping from 0 to 2 D was imaged at a rate of 100 fps in the right eye of a 24 and a 43 year-old subject. The OCT sequences were analyzed to extract the lens thickness for each frame. The dynamic response of the lens thickness was approximated with a first order exponential growth to extract dynamic descriptors including peak velocity, time constant and latency.

Results : Figure A shows OCT images of the anterior segment of the two subjects at the beginning (unaccommodated state) and at the end (accommodated state) of the acquisition. Figure B shows the lens thickness dynamics for each subject. Mean absolute changes in lens thickness, peak velocity, time constant and latency were comparable between subjects (Figure C). The lens was thicker in the older subjects, as expected. High sampling rate enables recording microfluctuations in lens thickness throughout the accommodation response in both subjects (Figure B – arrows), suggesting a more sophisticated fitting model might be needed to describe the dynamics.

Conclusions : The study demonstrates the capability of SS-OCT to provide dynamic biometry of accommodation with high speed (100Hz). The system enables detection of microfluctuations of accommodation that cannot be detected at lower speeds.

This is a 2020 ARVO Annual Meeting abstract.