Ciliary ganglion choline acetyltransferase activity in avian macrophthalmos

While present evidence fails to support an etiologic mechanism for myopia based on accommodation or choroidal blood flow, atropine exhibits anti-myopia activity in many species. Accordingly, we studied choline acetyl transferase (ChAT) activity in the ciliary ganglion, uvea and retina of chicks with experimental macrophthalmos to identify a potential pathway for the moderation of eye growth by cholinergic neurons. Following unilateral lid suture or goggle, chicks were reared for 1 week under one of four lighting conditions known to induce macrophthalmos or myopia. Ocular tissues and ciliary ganglia were assayed for ChAT activity by measuring the conversion of 14C-acetyl CoA to 14C-acetylcholine. For some chicks, the goggles were removed at 1 week, and ChAT activity was measured 2 or 7 days later. Depending on the rearing condition, ciliary ganglion ChAT activity was depressed from 16 to 28% ipsilateral to the lid suture; enzyme activity also was reduced in the choroid of visually deprived eyes under most conditions. In contrast, lid suture resulted in no consistent trend in ChAT activity in either the anterior uvea or retina. For chicks wearing a unilateral goggle and reared under a 12:12 hr light/dark cycle, ChAT activity was depressed in the ciliary ganglion, anterior uvea and choroid on the visually deprived side. Following goggle removal to allow recovery from myopia. ChAT activity in the ciliary ganglion and uvea was returned toward that of the control side. The ciliary ganglion may participate in a neural pathway influencing the development of form-deprivation myopia.