Altered Scleral Collagen Accumulation at the Posterior Pole of Eyes Developing Axial Myopia

Abstract

Abstract: : Purpose: The development of high myopia is associated with reduced scleral collagen accumulation in both humans and animal models of myopia. This reduction in collagen accumulation is consistent with the scleral thinning and dry weight loss which is reported in myopic eyes. The present study tested the hypothesis that reduced accumulation of fibrillar collagen results from both reduced collagen synthesis and increased collagen degradation. Methods: Collagen synthesis: Tree shrews were monocularly deprived of form vision for 5 days, using a translucent occluder (n=6). On the 5th day, [₃H] proline, a collagen precursor, was delivered by intraperitoneal injection and 9 hrs were allowed for its incorporation into new collagen fibrils. Scleral tissue was then collected and assayed for incorporated [₃H] proline and for hydroxyproline, an indicator of total collagen. Collagen degradation: Tree shrews were administered [₃H] proline 24 hrs prior to monocular deprivation (n=18). Animals were then deprived for either 0, 5, 12 or 24 days. Scleral tissue was collected at the end of these periods and assayed for [₃H] proline and hydroxyproline content. Changes in refractive error and eye size were monitored by retinoscopy and A-scan ultrasound. Results: Collagen synthesis: Scleral [₃H] proline incorporation was reduced at the posterior pole of the myopic eye, relative to the fellow eye, following 5 days of deprivation (-364%, p<0.01). Collagen degradation: Posterior scleral [₃H] proline content was similar in myopic and control eyes before deprivation (-18%) but was reduced in myopic eyes following 5 (-83%, p<0.05), 12 (-154%, p<0.05) and 24 (-115%) days of deprivation. Conclusion: Reduced scleral collagen accumulation at the posterior pole of myopic eyes is a result of both reduced collagen synthesis and accelerated collagen degradation. However, the degree of scleral collagen degradation is more consistent with the reported tissue loss. The present findings indicate that altered collagen accumulation is a major factor in the scleral thinning and tissue loss which occurs in eyes with high degrees of axial myopia.

Keywords: 481 myopia • 574 sclera • 403 extracellular matrix