Evidence That Increased Scleral Growth Underlies Visual Deprivation Myopia in Chicks

The authors evaluated three measures of scleral growth in chicks that were visually deprived with the use of translucent occluders. The authors sought to determine whether the ocular elongation and myopia that results from this deprivation is associated with increased growth of the sclera. The authors found that the dry weight of the sclera of deprived eyes increased 65% faster than that of nondeprived eyes. Furthermore, the uptake of labeled methionine and thymidine was significantly increased by visual deprivation, whether expressed as incorporation per sclera, per milligram of sclera, per milligram of protein, or per milligram of DNA. In addition, the amount of DNA and soluble protein was significantly greater in the scleras of deprived eyes than in those of nondeprived eyes. Finally, the degree of hydration of the scleras from deprived eyes was greater relative to their weight than that of the scleras from nondeprived eyes. These results suggest that visual deprivation causes increased cellular proliferation and increased protein synthesis in the sclera of chicks.