Expansion of the retinal pigment epithelium in experimental myopia.

Expansion of the retinal pigment epithelium was studied in neonatal chicks after one or two weeks of unilateral form vision deprivation to investigate altered ocular growth mechanisms in this experimental model of myopia. The area of individual retinal pigment epithelial (RPE) cells, measured in tangential sections, was greater in myopic eyes than in contralateral control eyes at both times. The mean RPE cell area in myopic eyes increased to the same extent as the area of the retinal pigment epithelium as a whole. In control eyes between one and two weeks, RPE cell expansion occurred predominantly in the periphery; in myopic eyes, it occurred more generally across the epithelium but was less pronounced in the temporal region. Given the absence of detectable mitotic figures in control and myopic eyes, expansion of the epithelial layer is attributable to passive stretch or growth of existing cells. Whether scleral growth or stretch occurs selectively beneath the areas of more pronounced RPE cell expansion is unknown.