The effects of blepharorrhaphy induced depression of corneal cholinergic activity

Unilateral lid closure for 8 or more days had previously been shown to reduce rabbit corneal epithelial choline acetyltransferase (ChAc) activity without affecting lactic dehydrogenase activity or thymidine, uridine, leucine and alanine incorporation rates. In the present study, the reduction in ChAc activity was found to be associated with a similar reduction in acetylcholine (ACh) content, to a mean value of 16 and 17%, respectively, of control eye levels. However, on reopening the lids, ACh levels recovered much more rapidly, achieving a mean value 67% of control values (P > 0·05) in 48 hr while ChAc activity was only 23% of control eye levels at 48 hr and required more than 30 days to fully recover. Unilateral lid closure of 10 days was also associated with a small increase in corneal thickness, 0·46±0·09 mm vs. 0·41±0·04 mm (P < 0·05), and reductions in standing electrical potential, 5·5±7·8 mV vs. 13·2±15·2 mV (P < 0·05), and short circuit current, 2·7±2·6 μA vs. 4·9±3·5 μA (P < 0·05). On re-opening the lids, the short-circuit current recovered within 24 hr, the corneal thickness within 3 days and the resting potential within 4 days. Administration of ACh 10^-4 m, pilocarpine 10^-4 m, eserine 10^-6 m or carbachol 10^-5 m to the epithelial side of corneas mounted in chambers immediately after reopening the lids failed to elevate either the standing electrical potentials or short-circuit currents; a causal relationship between cholinergic activity and corneal electrical phenomena could not be demonstrated.