Abstract
Purpose :
Studies have shown that axial length (AL) changes in response to myopic optical defocus in young adults. However, the range of myopic defocus used has been limited (≤ +3 D). Moreover, the interaction between myopic defocus and ambient light intensity on AL is not well-studied. The goal of this study was to assess AL change in response to increasing increments of myopic defocus under three different ambient light conditions.
Methods :
Healthy participants (ages 28.5±6.1 years, n=15) underwent three experimental sessions in a randomized order. At each session, participants first viewed a movie at 2 meters for 10 minutes. The room light was then adjusted to one of the three ambient light intensities (dim: <50 lux, moderate: ~500 lux, bright: ~2000 lux) and after 15 minutes, a Lenstar biometer was used to measure baseline AL. +2D was then added to the left eye. Participants continued to watch the movie, and AL was measured in both eyes after 15 minutes. Each 15 minutes, the defocus was increased to +4D and +6D, and Lenstar repeated. Upon removal of the final lens, recovery was assessed at 15 minutes. For each eye, the AL difference between the baseline measurement and each time point was calculated. The difference in AL between experimental and control eyes was analyzed with repeated measures ANOVA for sequential time points (four 15-minutes intervals) and light intensity (dim, moderate, bright).
Results :
Spherical equivalent refractive error and axial length were comparable between right and left eyes (control: -0.6±1.3 D and 23.56±1.00 mm; experimental: -0.6±1.3 D and 23.57±0.96 mm; P=0.49 and P=0.76, respectively). There was no significant AL change across the four time points (P=0.96) or between the three light intensities (P=0.83). Additionally, there were no significant interactions between time point and light intensity (P=0.81).
Conclusions :
Axial length did not significantly change in experimental eyes compared to control eyes following 15 minute intervals of monocular myopic defocus from +2D to +6D, regardless of ambient light intensity. Our results suggest that if axial length changes occur in response to myopic defocus, they may not be detectable with a Lenstar biometer.
This abstract was presented at the 2022 ARVO Annual Meeting, held in Denver, CO, May 1-4, 2022, and virtually.