The postnatal development of the retina in the normal and rodless CBA mouse: A light and electron microscopic study

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Abstract
The postnatal development of the retina in control (CBA/S) and rodless (CBA/Ki) mice was studied by light and electron microscopy. In the control mice, the major increase in retinal thickness occurs between birth and seven days. The inner and outer segments begin to grow into the optic ventricle between seven and ten days with their most rapid growth occurring between 12 to 15 days; by 35 days the retina appears mature. During development, the nuclear layers become thinner while the optic ventricle (layer of rods) and the plexiform layers become thicker. At birth, the mutant or rodless retina is indistinguishable from the control; however, the inner and outer segments fail to develop beyond the primitive seven‐ to ten‐day stage. At 15 days the outer nuclear layer becomes reduced to only a few nuclei in thickness. Many degenerating elements are found in the cavity of the optic ventricle and in the outer nuclear and plexiform layers. By 35 days the mutant retina lacks photoreceptors and is reduced in thickness to less than that at birth. The pigment epithelium is heightened in regions where degeneration is incomplete but becomes highly attenuated in regions where visual cell degeneration is complete. The optic ventricle contains the villous processes of the pigment epithelium and the fringe processes of the Müller cells. The outer limiting membrane is contiguous with remnants of the outer plexiform layer. Between the outer plexiform layer and the inner limiting membrane, the mutant retina is normal in appearance and dimension. The delayed appearance of the smooth endoplasmic reticulum of the pigment epithelium is implicated in the failure of outer segment maturation. The role of both Müller and pigment epithelial cells in removal of the products of retinal degeneration is discussed.