As the optic cup develops, an asymmetric invagination forms and leaves a groove, the choroid fissure, in the optic stalk. The adjacent ectoderm thickens to form the lens placode (a & b) which invaginates and (eventually) separates (c) from the ectoderm to form the lens vesicle.
The primary optic vesicle (a) becomes a double walled optic cup (c). With continued invagination the original lumen of the optic vesicle is reduced to a slit between 1) inner neural layer and 2) outer pigment layer of the optic cup (c).
Mesenchyme around the optic vesicle will contribute to the fibrous coats of the eye (sclera/cornea) externally and the choroid layer adjacent to the pigment layer. Mesenchyme also forms the hyaloid vessels (c) which pass in the choroid fissure, across the vitreous chamber, to supply the lens.