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Choroidal Regulation of Scleral Glycosaminoglycan Synthesis during Recovery from Induced Myopia

From the Department of Cell Biology, University of Oklahoma Health Sciences Center, Oklahoma City, Oklahoma.

PURPOSE. The present study was undertaken to examine the relationship between choroidal permeability and scleral glycosaminoglycan synthesis rates during the development of and recovery from form deprivation myopia.

METHODS. Form deprivation myopia was induced in chicks for 10 days and was followed by a period of unrestricted vision for 0 to 15 days (recovery). Choroidal permeability was quantified by measuring albumin leakage from choroidal blood vessels into suprachoroidal fluid using Evans blue. Scleral sulfated glycosaminoglycan synthesis was assessed on punches of sclera obtained immediately after extraction of suprachoroidal fluid for permeability measurements or after incubation with suprachoroidal fluid by measuring the amount of ³⁵SO₄ incorporated into glycosaminoglycans over a period of 4 hours at 37°C. Suprachoroidal fluid was subjected to size fractionation and proteinase digestion to characterize the bioactive fractions from recovering and control chick eyes.

RESULTS. Recovery from prior form deprivation was associated with a significant increase in choroidal permeability, compared with that of myopic eyes and contralateral control eyes, and was coincident with a significant decrease in scleral sulfated glycosaminoglycan synthesis rates in treated eyes compared with contralateral control eyes. Suprachoroidal fluid isolated from recovering chick eyes significantly inhibited scleral glycosaminoglycan synthesis compared with suprachoroidal fluid from control eyes (–54%; P < 0.01; ANOVA). Preliminary characterization of suprachoroidal fluid suggested that all inhibitory activity in suprachoroidal fluid fractions specific to recovering eyes is present in molecular weight fractions of less than 10 kDa.

CONCLUSIONS. The results of this study suggest that increased choroidal permeability coincides with a decrease in the rate of scleral glycosaminoglycan synthesis during recovery from myopia. The authors speculate that increased choroidal permeability may represent a mechanism for controlling the rate of delivery of bioactive factors to the sclera to regulate the rate of glycosaminoglycan synthesis in the posterior sclera.