Combined System for Dynamic Refraction and Ocular Biometry During Accommodation

Abstract

Purpose : Changes in ocular power during accommodation are the result of changes in lens shape. Yet, few studies have quantified the relation between ocular biometry and objective accommodative response. These studies typically rely on static measurements repeated at multiple accommodative demands. The goal of this project is to develop an instrument to dynamically measure the relation between changes in refraction and ocular biometry during accommodation.

Methods : The combined system includes a Shack-Hartmann aberrometer to measure refraction, a fixation target to stimulate accommodation, and a previous whole-eye OCT system for biometry (Ruggeri et al, Biomed Opt Exp 2012). The fixation target uses a two-channel Badal system that generates either step and ramp stimuli with vergences ranging from -20 D to +10 D. Refraction and OCT biometry are recorded sequentially by flipping a dichroic mirror. OCT images are processed using a semi-automatic segmentation software to quantify corneal and lens curvatures and intraocular distances. Accuracy of the refraction was assessed by comparing measurements on 23 eyes of 12 subjects (SE range: -9.25 to 2.25 D) with measurements acquired with a commercial autorefractor (KR-800, Topcon). Accommodation responses of three human subjects (ages = 21, 27, 31 years) to three ramp stimuli (2, 4, and 8 D at 0.25 D/s) were recorded in triplicate 25Hz (refraction) and 8.7 Hz (OCT). The responses were analyzed to correlate changes in refraction and biometry.

Results : Bland-Altman analysis shows a mean difference between the clinical autorefractor and custom-made aberrometer of -0.02 D ± 0.9 D (95% confidence limits). The accommodative responses of all three subjects had a similar behavior, with a 6 s latency followed by a linear response with time or accommodative demand up to maximal accommodation.

Conclusions : We demonstrate the feasibility of combined dynamic objective refraction and biometry during accommodation. Dynamic recordings provide faster and more precise quantification of accommodative responses.

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

 

(left) Photograph and (right) optical schematic of the combined system.

 

Accommodative response (D) versus change in lens thickness (mm) of 21, 27, and 31 year old subjects to all ramp accommodation stimuli at 0.25 D/s.