REDUCED EXTRACELLULAR-MATRIX IN MAMMALIAN SCLERA WITH INDUCED MYOPIA

The purpose of this study was to learn whether visual form deprivation , which produces myopia in the deprived eye, alters the scleral extrac ellular matrix in tree shrew, a mammal closely related to primates. Ax ial myopia was induced in 10 tree shrews by monocular deprivation impo sed with a translucent diffuser. The other eye in each animal was an u ntreated control. After 21 days of deprivation the refractive state an d axial component dimensions were measured and the eyes were assayed f or levels of DNA, hydroxyproline, and sulfated glycosaminoglycans (GAG s) in samples of the sclera and the cornea. In comparison to the open control eye, the deprived eyes became myopic and elongated. In the scl era, DNA levels were not significantly changed from the control eye. S ulfated GAG levels were significantly lower in the deprived eyes, as c ompared to the control eyes, at the posterior pole (-15.6%), at the na sal equatorial region (-18.1%), and in the rest of the sclera (-11.6%) . The hydroxyproline level was significantly lower only at the posteri or pole (-11.8%). Levels of sulfated GAGs were significantly reduced r elative to DNA and relative to hydroxyproline in the total sclera. No significant changes were found in the cornea. The lower level of sulfa ted GAGs throughout the sclera of the deprived eyes, as compared with the control eyes, suggests that the deprived sclera contained less pro teoglycan, or that the proteoglycans were less glycosylated or less su lfated. In contrast, the regional reduction of hydroxyproline suggests that collagen accumulation was specifically reduced only at the poste rior pole of deprived eyes. These results suggest that form deprivatio n slows or reverses the normal process of extracellular matrix accumul ation in the sclera of this mammal. This may allow the sclera to be mo re distensible, permitting the vitreous chamber elongation and resulta nt myopia.