Abstract
Purpose :
We have studied the effects of prolonged equiluminant dynamic ON or OFF stimulation on refractive development, choroidal thickness (ChT), axial length (AL) and dopamine release in chicks wearing monocular negative lenses.
Methods :
33 chicks were monocularly treated with negative lenses and subjected to one of the three light regimens: room light (“control”, 500 lux, n=11), dynamic ON stimulation (300 lux, n=15) or dynamic OFF stimulation (300 lux, n=7). Dynamic ON or OFF stimuli (developed under Visual C++ 8.0) consisted of about 2000 small squares on a computer screen that had a saw–tooth shaped monochrome grey temporal luminance profile, either with a rapid ON and slow linear decay (ON stimulus) or vice versa (OFF stimulus). All squares were randomly phase shifted with respect to each other at 1Hz. During the light cycle, chicks were in a “chicken discotheque” (4 large computer screens represented the walls). Refraction, AL and ChT were measured before and after experiment with automated IR photoretinoscopy, A-scan ultrasound, and SD-OCT, respectively. After 7 days of exposure, retina and vitreous were prepared for dopamine (DA) measurements with HPLC-ED.
Results :
Eyes with negative lenses developed more myopia under both ON and OFF stimulation (ON -3.66±0.14 and OFF -3.41±0.23D vs control -2.40±0.37D; p<0.001 and p<0.05, respectively, ANOVA, followed by a Tukey-Kramer HSD test). Myopia with the lenses was accompanied by thinner choroids under all illumination conditions (ON -7.79±12.60 µm, OFF -23.50±9.31 µm, control -2.36±9.06 µm) while fellow eyes developed thicker choroids (+34.21±8.12, +34.05±9.55, and +23.80±7.53, respectively, all p<0.01). Lenses caused longer axial lengths in all cases (ON +0.48±0.04, OFF +0.46±0.08 mm, control +0.43±0.06; all p<0.001). After 7 days, lens treated eyes had reduced DA (ng/0.1g wet weight) under all illumination conditions (ON 0.71±0.08 vs ON+lens 0.32±0.03; OFF 0.33±0.03 vs OFF+lens 0.17±0.02; control 0.47±0.05 vs control+lens 0.21±0.02; all p<0.001). However, ON stimulation produced elevated levels of vitreal DA in all cases, compared to OFF stimulation and control (p<0.05 to p<0.001).
Conclusions :
Despite that we did not observe bi-directional changes in refractions during prolonged dynamic ON or OFF stimulation under equiluminant conditions, ON stimulation increased DA release, no matter whether a lens was worn or not.
This abstract was presented at the 2019 ARVO Annual Meeting, held in Vancouver, Canada, April 28 - May 2, 2019.