Development of Eye in frog

The sensory element, the retina arises directly from the brain. The other accessory structures originate from the mesoderm and Ectoderm. During the tail bud stage, a pair of ventro - lateral evaginations develop from the wall of the diencephalon called optic vesicles .The basal part of optic vesicle becomes constricted by the convergence of surrounding mesoderm to form a tube known as optic stalk. The cavity of optic vesicle called optocoel, is continuous with diocoel. The optic vesicle grows and comes in contact with head ectoderm. Now, its ventro - lateral wall flattens and invaginates to form a double walled cup called optic cup. The invagination of optic cup obliterates the optocoel and the inner and outer walls are therefore brought in the close proximity. The infolding of optic vesicle is also extended to the  side of the optic stalk and converts it into a double walled groove callled choroid fissure.
 
The ectoderm at the point of contact with optic vesicle thickens in form the lens placode which invaginates to develop a vesicle called lens vesicle. It pinches off from the head ectoderm and comes to lie within the ring of optic cup supported by suspensory ligaments. The cavity of lens vesicle is obliterated. The cells of the inner wall of lens becomes elongated to form lens fibres and the outer wall as cuboidal npithelial cells. The outer ectoderm extends over the lens and in conjunction with mesenchyme forms a double layered cornea which modifies into a thin and transparent membrane over the lens. A small  cavity, aqueous chamber, develops between the lens and cornea a becomes filled with aqueous humour. The outermost wall of the optic cup is a pigmented layer tha comes in contact with the inner sensitive layer, the retina. The cells the retina differentiate into rods and cones which point away from the source of light. The inner margin of the retina consists of neuroblas the fibres of which pass over the surface of the retina and leave the optic cup by the way of choroid fissure as the optic nerve. Then, they passing the wall of the optic stalk which serves as guiding path for optic nerves to reach the diencephalon. The optic nerve fibres cross at the junction of the optic chiasma at the floor of the diencephalon. Eventually, the choroid fissure will close around the blood vessels and nerves supplying the eye. The ventral margin of optic cup where the choroid fissure is originating fuse to form the choroid knot from where the cells of the iris arise in the eye. The large cavity between the lens and retina differentiates into vitreous chamber which becomes filled with a viscous fluid known as vitreous humor derived from cells of the retina and lens. The inesenchyme around the optic cup gives rise to the connective tissue of choroid coat that surrounds the pigmented layer of the eye. The sclerotic lyer also originates from the mesenchyme. The sensory layer of retina .ind part of cornea are ectodermal in origin while the blood vessels, connective tissue, cartilage and part of cornea are mesodermal structures.