THE EFFECT OF NITRIC-OXIDE SYNTHASE INHIBITOR ON FORM-DEPRIVATION MYOPIA

Purpose. Form-deprivation myopia (FDM) is believed to result principal ly from actions of substances that modulate information processing in the retina. We used a chick model to investigate what role nitric oxid e (NO), a gaseous neuromodulator might play in the development of FDM. Methods. We injected different concentrations of the NO synthase inhi bitor N omega-nitro-L-arginine methyl ester (L-NAME) (30 mi) into the left eyes and the same volume of saline into the right eyes of 6-day-o ld chicks, Both eyes of most chicks were occluded for 6 days with tran slucent goggles. After removal of the goggles, the refraction was meas ured by retinoscopy and the axial lengths with an A-mode ultrasound. I n some chicks we measured the concentration of NOx (nitrite and nitrat e) in the retina. A few chicks, not wearing occluders after injection of L-NAME and saline, ERG and refraction, were examined 6 days after t he treatment. Results, In chicks that wore occluders, refractive error and axial length were significantly less affected in eyes injected wi th L-NAME (180, 360, or 540 mM) compared to control (right) eyes. ERG changes were reversible, except in eyes injected with the highest conc entration (540 mM) of L-NAME. The eyes of chicks, Injected with L-NAME and reared without occlusion, had normal refractive values. After 6 d ays of form deprivation, the concentration of NOx in the retina of eve s injected with L-NAME (180 mM) was significantly less than the concen tration in eyes injected with saline. Conclusions. The injection of L- NAME before occlusion of developing chick, eyes leads to reversible mo difications in retinal function and inhibits the development of form-d eprivation myopia.