RETINAL DOPAMINE IN THE RECOVERY FROM EXPERIMENTAL MYOPIA

Purpose. To address further a possible role for retinal dopamine in po stnatal eye growth, we studied the response of retinal dopamine in eye s of chicks recovering from myopia. Methods. Newborn chicks either rec eived a unilateral translucent goggle to induce form deprivation myopi a or were reared with unimpaired visual input. The goggle was removed from half of the chicks on day 7. Myopic, recovering and control never -goggled chicks were studied on days 7, 9 and 14. Eyes were enucleated postmortem and measured in axial and equatorial dimensions with calip ers. Retinal levels of dopamine and its principal metabolite 3,4-dihyd roxyphenylacetic acid (DOPAC) were assayed by high performance liquid chromatography with electrochemical detection. Results. Compared to co ntralateral and control eyes, retinas of goggled eyes at each time poi nt had reduced levels of dopamine and DOPAC and a lowered calculated D OPAC/dopamine ratio, an index of dopamine metabolism. In eyes recoveri ng from myopia, all biochemical parameters showed prominent increases by 2 days after goggle removal and had reached the level of both contr alateral eyes and control eyes by one week after goggle removal. As ev idence of a contralateral effect, the retinas of open eyes of chicks w earing a unilateral goggle demonstrated equal dopamine levels but redu ced DOPAC compared to eyes of never-goggled chicks. Conclusion. An ear ly rise and eventual normalization of retinal dopamine, DOPAC and the DOPAC/dopamine ratio correlate with recovery from myopia. Combined wit h recent results from lens rearing experiments, these findings suggest that dopaminergic amacrine cells may participate in visually guided e ye growth regulation and not just in the myopia response to visual for m deprivation. The retinal biochemical alteration in eyes contralatera l to a goggle indentifies a previously unappreciated binocular interac tion in the chick.