Write a detailed note on the eye of frog.

EYE OF FROG:

The frog has two eyes one on each side of the head. 

(i) Eyeball: 

The eyeball is almost spherical. It has a wall composed of three layers or coats. 

(i) Outer Layer:

It is the hard, outer most layer of the eye. It consists of an almost opaque sclera or sclerotic layer. The anterior transparent part of the scelerotic layer is called cornea. which is connected, in a continuous ring. 

Function: 

Sclerotic layer provides shape to the eyeball. 

(ii) Middle Layer:

Its consists of a choroid layer , which is well supplied with blood vessels providing nutrients and oxygen. An eye deprived of oxygen will be irreparably damaged.A black or dark pigment makes the choroid layer totally opaque and lightproof

The circular iris, ciliary muscle and ciliary body from the front position of the middle layer.

The central perforation of the eye is called pupils of eye.

Function:

 (1) The choroid provides nourishment and oxygen to the eye. 

(2) The iris controls the amount of light entering the eye through pupil. 

(iii) Inner Layer:

 The innermost layer of the eyeball is called retina: Retina consists of sensory cells called the rods and cones. The rod cells are stimulated by low light intensities while the cone cells are stimulated by high light intensities. Only the cone cells are sensitive to coloured light. Function:

Retina acts as a screen, which receives the image of objects, focused by the lens. 

(iv) Aqueous Humour: 

The space between the lens and cornea is filled with aqueous humour, which is quite watery. 

(v) Lens: 

It is a clear biconvex lens held in position by suspensory ligaments connected to the ciliary body and muscles. Function: It focuses light on the retina. 

(vi) Vitreous Humour: 

A clear jelly like vitreous humour completely fills the eyeball behind the lens and ciliary muscles. 

Function: 

The spherical shape of the eye is maintained by constant pressure of the fluid components of the eye. 

(vii) Optic Nerve: 

Nerves connect with the retina sensory cells and join together at one position at the back of the eye to form an optic nerve. At the point called the blind spot where the optic nerve leaves the eyeball, there are no sensory cells. 

Function: 

Optic nerve connects the eye with the brain region that interprets sight.