Effects of chronic exposure to 0.5 Hz and 5 Hz flickering illumination on the eye growth of guinea pigs.

Aims: To investigate the effect of prolonged flickering illumination exposure on the growth of the guinea pig eye. Methods: Thirty-six 2-week-old guinea pigs were randomized to one of the three treatment groups (n = 12 for each). Two strobe-reared groups were raised with a duty diurnal cycle of 50 % at a flash rate of 0.5Hz and 5Hz respectively. Illumination intensity varied between the minimum-maximum light levels of 0-600 lux during each cycle. The control group was exposed to steady 300 lux illumination. All animals underwent refraction and biometric measurements prior to and after 2, 4, 6, 8, 10 and 12 weeks of treatment. Finally, flash electroretinograms were compared, and retinal microstructures were examined. Results: There was a significant correlation between refractive errors and axial eye elongation, with myopia increasing between 1.5 and 3.4 D per mm eye elongation. After 12 weeks of treatment, the animals raised in 0.5Hz flickering light were 5.5 +/- 0.4 D more myopic than the group raised in continuous illumination, followed by the group raised at 5Hz flicker light which was about 2.2 +/- 1.3 D more myopic. In animals raised in flickering light of 5 or 0.5Hz for 12 weeks, the implicit time of the a-wave was delayed by 4 and 8.5 ms, respectively. At this time, the outer segment disc membranes were found deformed and detached. Conclusion: Chronic exposure to 0.5 and 5Hz temporally modulated illumination induces electrophysiological and histological changes in retinal activities that alter the emmetropization of the guinea pig eye.