Tunica fibrosa and tunica vasculosa

As the optic cup enlarges, the surrounding mesenchyme condenses. The mesenchymal cells flatten and surround the sphere of the optic cup. From this condensed mesenchyme, the tunica fibrosa of the eyeball arises, which is similar to the dura mater. Its posterior part becomes the sclera while its anterior part becomes transparent and forms the substantia propria of the cornea. The vascular layer, i.e. the tunica vasculosa of the eyeball (uvea), develops between the sclera and retina. The mesenchyme of the tunica vasculosa in the region of the optic part of the retina differentiates into the choroid. The mesenchyme thickens considerably at the anterior aspect of the optic cup, thus forming the ciliary body. The fibres of both the sphincter and dilator pupillae muscles develop from the outer layer of the optic cup in the region of the iridal part of the retina. The eyelids are formed from small skin folds. These folds grow towards each other and join in the middle around month 3. During month 6, the eyelids open again.