Modulation of scleral DNA synthesis in development of and recovery from induced axial myopia in the tree shrew

Visually modulated scleral extracellular matrix remodelling is associated with the development of, and recovery from, induced axial myopia in the tree shrew, a commonly used mammalian model of refractive error development. The involvement of scleral cell proliferation in this process was investigated using [3H] thymidine. Tree shrews were monocularly deprived of pattern vision, using translucent occluders, or the retinal image was optically defocused, using negative lenses, over a period of 5 days. A further group was monocularly deprived for 5 days, then allowed 3 days of binocular recovery. A control group of binocularly open animals was employed to establish normal parameters. On the final day of the experimental period, [3H] thymidine was administered by intraperitoneal injection, then optical and biometric measures were taken and tissue samples collected for assay. Incorporation of [3H] thymidine into cellular DNA was measured in proteinase K digests, following precipitation with trichloroacetic acid. After 5 days, significant amounts of myopia were present in the treated eyes of both form-deprived [-7. 0+/-0.7 Dioptres (D), group mean+/-s.e.m.; P<0.01] and lens-defocused animals (-6.2+/-0.9 D;P<0.01). After 3 days of recovery, 50% of the refractive error had been compensated for, predominantly through shortening of the vitreous chamber in the treated eye. Reduced levels of [3H] thymidine incorporation were observed in sclera from both groups of myopic animals (form-deprived, -34.3+/-9.9%;P<0.05 and lens-defocus, -32.8+/-4.5%;P<0.005). Increased levels of [3H] thymidine incorporation were found in the sclera of recovering animals (+144.0+/-43.2%;P<0.05). The results show that changes in regulation of cell proliferation, during the development of myopia, are visually mediated and inversely related to the direction of change in ocular size. This implies that alterations in the scleral fibroblast population are involved in the modulation of scleral matrix turnover during myopia development.