At first, the optic cup is present only above the optic stalk or the future optic nerve. In other words, only the upper optic primordium forms initially. The first ganglion cells arise here, close to the junction of the optic stalk. The lower half of the eye develops later, when the inferior lobes of the optic cup grow. The inferior lobes later enclose the optic stalk and the central retinal artery and vein. The borders fuse together. This causes the site of departure of ganglion cell axons from the retina to narrow down to a circular region of the eye, the future papilla of the optic nerve. Due to the unequal growth of the retina, the optic papilla becomes shifted close to the centre of the retina.
As the optic cup develops, the ectodermal lens placode invaginates to form the lens pit (fovea lentis). This forms the lens vesicle, which becomes separated from the surface ectoderm. The cells of the wall of the lens vesicle facing the retina become elongated and develop into lens fibres. The latter progressively fill the cavity of the vesicle (lens ventricle).