Abstract
Abstract: :
Purpose: To study the effects of light regime and hormones on the growth of the cornea without inputs from the rest of the eye and body, isolated corneas were cultured, and grown with or without exposure to melatonin or to melatonin plus retinoic acid in constant light (CL). Methods: Chicks were raised for 17 days in CL. Corneas were harvested, weighed, and then cultured for 14 days on 0.8% agar cushions in DMEM. Media was changed every 3 days. One cornea of each animal received hormone treatment, the other cornea from the same animal was used as a control and received unaltered media. Groups were: CL (control, no humoral factor added); CLM (melatonin added with each fresh change of media to a concentration of 60 ng/ml); CLRA (retinoic acid saturated ETOH added at 1 microliter/ml to fresh DMEM); CLMRA (melatonin plus retinoic acid, same concentrations as before). After 14 days, corneas were weighed, then dried to obtain dry weights. Sample corneas from each group were not dried, but fixed for histological assessment. Results: After 14 days in culture, the corneal epithelium was healthy. The endothelium was continuous, but fewer endothelial cell nuclei were observed than typical of in vivo corneas of the same age. Stromal cells appeared to be healthy but were disorganized compared to in vivo corneas. The fresh appearance of cultured corneas differed from in vivo corneas in that they were much thicker, and slightly cloudy in appearance. Wet weight differed significantly for the group treated with melatonin. These 8 corneas gained an average of 6.15 mg (±0.41) compared to 7.85mg (±0.28) among 30 controls, p=0.0095. CLRA and CLMRA corneas did not differ significantly from controls. There were greater differences among the groups in hydration status, measured as (final dry weight/(final wet weight/final dry weight)), as shown below (Fisher's PLSD test). Treatment with melatonin resulted in less hydrated corneas. Differences in hydration states of corneas
Conclusions: We interpret these differences to mean that melatonin caused the corneas to absorb less water, probably due to differences in the glycosaminoglycan content of the stromal matrices. Retinoic acid appears to counteract this effect of melatonin.
Keywords: cornea: stroma and keratocytes • melatonin • hyperopia