Prenatal development of the eye in the golden hamster.

Prenatal development of the eye in golden hamsters is described at the light microscopic level as twelve periods based on salient morphological features. Period one includes shallow and deepened optic sulci in the cephalic neural plate and closing prosencephalon. Period two shows V-shaped prosencephalic evaginations, and Period three, bulbous vesicles. Contact of the retinal disc and lens placode at Period four precedes presumptive retinal invagination and lens pit formation during Period five. During Period six an open lens vesicle, precociously expanded dorsal and lateral optic cup regions and widespread optic fissure margins are evident. A spherical lens lumen, deepened optic cup and narrow optic fissure characterize Period seven. At Period eight posterior lens fibers are elongated, the optic cup is expanded ventrally, and optic fissure margins are juxtaposed or fusing. By Period nine the lens lumen is nearly or completely occluded, the optic fissure is essentially fused and axonal fibers are exiting from the globe. During Period ten corneal components are associated, axonal processes extend to the diencephalon, and lid folds cover more than half of the cornea. By Period eleven eyelids are fused. Anteriorly the pigmented epithelium is thickened and densely pigmented; outer and inner neuroblastic retinal layers are clearly distinguishable. Period twelve is marked by conspicuous anterior folds of pigmented epithelium; a relatively anuclear zone virtually separates outer and inner neuroblastic layers of the retina.