Structural and ultrastructural changes to the sclera in a mammalian model of high myopia

PURPOSE. The development of high myopia is associated with scleral thinning and changes in the diameter of scleral Collagen fibrils in humans. In the present study, the association between these scleral changes and the losses in scleral tissue that have previously been reported in animal models were investigated to determine the relationship between changes in Collagen fib ril architecture and thinning of the sclera in high myopia. METHODS. Myopia was induced in young tree shrews by monocular deprivation o f pattern vision for short-term (12 days) or long-term (3-20 months) period s. Scleral tissue from normal animals over a wide age range (birth to 21 mo nths) was also collected to provide data on the normal development of the s clera. Light and electron microscopy were used to measure scleral thickness and to determine the frequency distribution of Collagen fibril diameters i n the sclera. Tissue loss was monitored through measures of scleral dry wei ght. RESULTS. Significant scleral thinning and tissue loss, particularly at the posterior pole of the eye, were associated with ocular enlargement and myop ia development after both short- and long-term treatments. However, Collage n fibril diameter distribution was not significantly altered after short-te rm myopia treatment, whereas, from 3 months of monocular deprivation onward , significant reductions in the median Collagen fibril diameter were noted, particularly at the posterior pole. CONCLUSIONS. The results of this study demonstrated that loss of scleral ti ssue and subsequent scleral thinning occurred rapidly during development of axial myopia. However, this initial tissue loss progressed in a way that d id not result in significant alterations to the,collagen fibril diameter di stribution. In the longer term, there was an increased number of small diam eter Collagen fibrils in the sclera of highly myopic eyes, which is consist ent with findings in humans and is likely to contribute to the weakened bio mechanical properties of the sclera that have previously been reported.