Morphological changes of choriocapillaris in experimentally induced chick myopia

Background: To clarify the mechanism of chorioretinal atrophy, the morphological changes in choriocapillaris (CC) in myopic chick eyes were investigated. Methods: Form deprivation myopia was induced in 40 chicks by unilateral eyelid suturing. Vascular corrosion casts of the choroidal vasculature were examined with scanning electron microscopy (SEM). Structural changes in CC capillaries were also examined with transmission electron microscopy (TEM). Results: SEM examination of the casts showed that the CC capillaries in the contralateral control eyes formed an extremely dense network with round or oval intercapillary meshes, whereas the capillaries in the myopic eyes were less dense with wider and more ir regular intercapillary meshes. As evidenced with morphometrical analysis, CC in the myopic eyes 4 weeks and older exhibited significantly lesser density and capillary diameter and significantly greater center-to-center distance between adjacent intercapillary meshes than in the control eyes. With TEM, most of the capillaries in the myopic eyes were found to be almost devoid of endothelial fenestrations and had narrowed lumina, particularly evident after the 4th week. Conclusion: These results suggest that the decreased CC density caused in myopic chick eyes may be due partly to capillary atrophy and partly to overall stretch of the capillary network caused by abnormal enlargement of the myopic eyes.