Fine Structure of the Retinal Pigment Epithelium, Bruch's Membrane, and Choriocapillaris in the Northern Pike (Esox lucius)

The fine structure of the retinal pigment epithelium, Bruch's membrane, and the choriocapillaris has been studied by light and electron microscopy in the adult northern pike (Esox lucius).The pigment epithelium is composed of a single layer of large cells. Each epithelial cell has abundant mitochondria, smooth endoplasmic reticulum, myeloid bodies, phagosomes, and pigment granules. Rough endoplasmic reticulum and ribosomes are scarce.The scleral or basal border of the epithelial cell is not infolded whereas the vitreal or apical surface displays numerous, fine, elongated processes which surround the inner and outer segments of the photoreceptors.Bruch's membrane is composed of three layers. The innermost layer is the basal lamina of the pigment epithelium. The outermost layer is the basal lamina of the choriocapillaris endothelium. Between these basal laminae is a layer of fine fibrils. The overall thickness of Bruch's membrane is 3.5–4 μ posteriorly.The endothelial wall of the choriocapillaris bordering Bruch's membrane is typically very thin but nonfenestrated. Vesicles are common in the endothelial cytoplasm.This region of the pike eye differs morphologically from that described for most other vertebrates.