Abstract
Purpose :
We had previously found that simulated chromatic defocus, imposed by spatially filtering the RGB channels on a computer screen, induces changes in choroidal thickness already after 45 minutes. In emmetropes, simulated defocus in the blue induced thicker choroids and eye shortening, while simulated defocus in the red induced thinner choroids and eye elongation. Strikingly, myopic retinas were not responsive to these stimuli, suggesting that they may no longer detect longitudinal chromatic aberration (LCA). To further study this hypothesis, we compared accommodation to visual targets with simulated LCA, as well as visual acuity and contrast detection thresholds in monochromatic light in emmetropic and myopic young human subjects.
Methods :
Seventeen participants (7 myopes and 10 emmetropes, average age: 25±4 years, refraction range: 0.25 to -5.5D) took part in the experiments. Accommodation responses to targets displayed on 25” computer screen (1920x1080px), presented at 86 cm distance, were binocularly measured by infrared photorefraction. Six images were presented in sequence: a red cross on black background, a blue cross on black background, a white cross on black background that was digitally low pass filtered in the blue or red channel, and two photographs that were low pass filtered either in the blue or the red. Visual acuity and contrast detection thresholds were measured monocularly with eyes covered with cut-off filters (red 610 nm and blue 490 nm).
Results :
As expected from LCA, a red cross induced significantly more accommodation than a blue cross (difference in emmetropes: 0.4D, p<0.001). Low pass filtering the red channel in the displayed crosses or photographs induced more accommodation than low pass filtering the blue channel (difference in emmetropes: cross: 0.12D and image: 0.13D, both p<0.05). Strikingly, accommodation in myopic eyes was not affected by simulated LCA. No differences in blue or red light were found in visual acuity or contrast detection thresholds between myopes and emmetropes.
Conclusions :
Simulated chromatic aberration, embedded in fixation targets or photographs, affects accommodation in emmetropes (blue low pass filtered: less accommodation, red low pass filtered: more accommodation). Strikingly, such effects were lacking in myopes and cannot be explained by differences in visual acuity or contrast detection thresholds in red and blue.
This abstract was presented at the 2023 ARVO Annual Meeting, held in New Orleans, LA, April 23-27, 2023.