HUMAN EYE

The eye is the organ that allows us to see the world around us. It is perhaps the most wonderful and perfect optical instrument. Without eye, all other optical instruments would have no value at all. 

The main part of the human eye are : cornea, iris, pupil, eye-lens, aqueous humour, optical nerve, blind spot, retina and ciliary muscles.

1- Sclerotic: The human eye is a dark spherical chamber filled with a transparent fluid. It consists of an eye ball having a diameter of about 25mm. The walls of the eye ball consist of two major layers. The outer covering is known as "Sclerotic layer". It is tough opaque white substances. It forms the white portion of the eye.

2-Cornea: The front of this coating forms a curved section known as "Cornea". It is made of a transparent substance and is bulging outwards. The light coming from objects enters the eye through cornea. 

3-Iris: Just behind the cornea is the iris( or coloured diaphragm
) . The colour of iris is different for different individuals depending upon the pigments present in it. 

4-Pupil: There is a hole in the middle of the iris which is called Pupil of the eye. The pupil dilates or contracts depending upon the amount of light available.

 5-Eye lens: Behind the pupil and the iris is the eye lens. It is a convex lens made of a transparent material like jelly, made of proteins. The eye lens is kept in its position by a strong elastic frame made of 'ciliary muscles'. The focal length of eye lens can be changed by the action of ciliary muscles.

6-Retina: The screen of the eye ball where the images of the objects are formed, is called 'Retina'. It is located behind the eye lens at the back portion of the eye. The retina is a highly sensitive surface made up of nerves, rods and cones and communicates with the brain through the optic nerve. The least sensitive part of  the retina is called as the  'blind spot' and most sensitive point is called as the 'yellow spot'.