[Mechanism of axial elongation and chorioretinal atrophy in high myopia]

Myopic chorioretinal atrophy with axial elongation is one of the main factors of visual impairment in high myopia. To clarify the causes of this chorioretinal atrophy (CRA), the mechanism of ocular axial elongation was investigated from the effects of growth factors on experimental myopia models. From the analysis of large numbers of humans with extreme myopia, the factors causing CRA and the process of progression of this atrophy were also studied. I. Mechanism of ocular axial elongation Myopic change of 20 to 30 diopters occurred in chicks when they wore translucent or black opaque goggles for 2 weeks. But when they were fed under dark conditions for 24 hours, myopic change did not occur, and even when the goggles were worn, only slight myopic changes occurred. Thus, it appeared that light was necessary for myopic change and an increase in temperature caused by the goggles had little influence on the myopic change. In light microscopic observations, the posterior sclera of myopic chick eyes had thicker cartilaginous sclera and thinner fibrous sclera than the normal controls and abnormal proliferation of chondrocytes was seen at the border area. To investigate the changes in cell proliferation at 3 different locations (periphery, equator, posterior pole) of the sclera, the ratio of positive cells in PCNA, Decorin, b-FGF, TGF-alpha, TGF-beta, IGF-II, and phosphotyrosine were studied immunohistologically. Positive ratios were higher at the posterior pole of the treated myopic eyes for all factors, except for b-FGF and TGF-alpha. We estimated that the proliferation of chondrocytes and revelation of growth factors were higher at the posterior pole of the sclera in the experimental myopic eye than in the control eyes. In electron microscopic observations, proliferation of chondrocytes in cartilaginous sclera was found and small diameter collagen fibrils with a large amount of ground substance were observed in the fibrous sclera. These observations were similar to those of the sclera before hatching. It appeared that the sclera of the experimental myopic eyes remained in the pre-hatching condition. In co-culture experiments of the cultured condrocytes of cartilaginous sclera and the retina (retinal pigment epithelium (RPE) excluded), proliferation of the chondrocytes was suppressed significantly (p < 0.05). On the other hand, in the co-culture of chondrocytes and RPE-choroid, increase of the chondrocytes was induced (p < 0.05).(ABSTRACT TRUNCATED AT 400 WORDS)