Abstract
Purpose :
To evaluate the lack of accommodative activation during the Direct Subjective Refraction (DSR) as a reason for its accuracy
Methods :
DSR uses a tunable lens projected onto the pupil’s eye to induce periodic defocus changes at 15Hz and 0.25D of amplitude. Subjects minimize flicker perception on a bichromatic (red/blue) stimulus by varying the mean optical power. The position of the minimum flicker provides the refractive error. For comparison, a blur-minimization (BM) task was also performed using a monochromatic version of the stimulus. Subjects had to indicate whether the stimulus was in focus. A PlusOptix Power Refractor II was used to monitor the dynamic accommodative response during the DSR and BM tasks. Three young subjects (29±2yr) performed 10 alternating trials, with initial myopic (+1.5D) and hyperopic defocus (-1.5D, which could be accommodated). Temporal accommodative changes >0.5Hz (i.e., microfluctuations) were removed. Negative accommodative responses/speeds during repetitions represent activation, and positive represent relaxation. Mean measurement time and standard deviation (repeatability) across the 10 repetitions were compared
Results :
In the BM task, hyperopic defocus was accommodated as expected but myopic defocus was not (mean response -0.65±0.26 and -0.01±0.11D, respectively, Wilcoxon test p<.05). Remarkably, the accommodative response remained stable in the DSR task (hyperopic and myopic repetitions -0.23±0.24 and -0.08±0.26D, p>.05). In the BM task, the mean speed for hyperopic and myopic defocus was -0.39±0.24 and 0.11±0.08 D/s respectively (p<.05), whereas in the DSR task the mean speed hardly changed between hyperopic and myopic repetitions (0.01±0.05 and 0±0.06 D/s, p>.05). In addition, the DSR task was on average more repeatable (±0.22D) than the BM task (±0.73D). The time per repetition was very similar (mean 12.5±5.5s for DSR and 7.2±1.6s for BM)
Conclusions :
The temporal defocus wave of the DSR virtually eliminates the accommodative response during subjective refraction. This result explains the increased precision of the DSR task compared to BM, and could lead to refractive error measurements that do not require fogging or cycloplegia
This abstract was presented at the 2024 ARVO Annual Meeting, held in Seattle, WA, May 5-9, 2024.