Abstract
Purpose :
Early observations of increased prevalence of myopia in people who engage in near work blamed excess accommodation. The near accommodation reflex is accompanied by pupil constriction. The photopic pupil response (PR) is mediated by cones and intrinsically photosensitive retinal ganglion cells containing melanopsin, with a peak sensitivity at 480nm. We asked whether the PR to 480nm light was modified in myopic mammalian eyes.
Methods :
Guinea pigs wore a -6D lens on one eye from 6-13 days of age with white (n=6) or blue (n=6) luminance matched overhead LED lights on a 12/12 h cycle. After 7 days, lenses were removed and the direct PR to a blue LED (48010 nm) was repeatedly measured in each eye for 3 different luminance’s with an IR video camera in dark-adapted animals. Refractive error was subsequently measured with cycloplegia. The percent reduction in pupil diameter from the start of the trial to maximum constriction was calculated.
Results :
Both groups developed myopia whether raised in blue or white light (difference between eyes of -5.8±1.3D, p<.01 and -3.6±0.6D, p<.05 respectively). In fellow eyes, PRs were 2.7% greater in animals raised in blue compared to white light (Fig. 1, p = .011). The PR of lens-wearing eyes was greater than fellow eyes (increase of 3.6% for blue; and 4.2% for luminance matched white light (Fig. 1, p=.040 and .006 respectively). The larger the starting size of the pupil, the greater the constriction but this could not explain the enhanced constriction in lens-wearing eyes since their pupil starting size was smaller than in control eyes (Blue: 4.45 Vs 4.36 mm, p=.003; White: 4.54 Vs. 4.45 mm, p=.03).
Conclusions :
Young guinea pigs rapidly compensate for a -6D lens whether raised in blue or white light. One week of continuous negative lens wear significantly reduced pupil diameter and increased the PR to 480nm light. Exposure to hyperopic defocus requires greater accommodation and smaller pupils to see clearly. The pupil effects continued in myopic eyes when lenses were removed, suggesting residual effects persist and are not stimulus driven. The contribution by blue cones versus melanopsin to the observed enhanced pupil response in myopic eyes remains to be elucidated.
This is a 2020 ARVO Annual Meeting abstract.