The transparent tissues of the eye are the cornea, the aqueous, the lens, the vitreous, the retina and the conjunctiva. Morphologically they may be classified as follows :
Epiblastic Mesoblastic Conjunctiva Aqueous Cornea Vitreous Lens Retina
Preponderantly they are of epiblastic origin, but the aqueous, as far as present belief is concerned, must be classified as mesoblastic together with the vitreous. Here, then, are tissues from two distinct embryonic sources, following widely divergent courses of differentiation, occurring nevertheless in the same location with the common attribute of transparency, and only in that location. It is true that translucence is found elsewhere in the body, but usually as a function merely of the thinness of the structure involved. However, the transparency of the ocular media occurs irrespective of the characteristic of thinness, as exemplified in the vitreous and the lens, although this characteristic occurs in diminishing amount in the cornea,