Study Notes On Human Eye

HUMAN EYE

The human eye is like a camera. Its lens system forms an image on a light-sensitive screen called the retina.


The eyeball is approximately spherical in shape with a diameter of about 2.3 cm.
The eye lens forms an inverted real image of the object on the retina.


RETINA -> The retina is a delicate membrane having enormous number of light-sensitive cells.

CORNEA ->  Light enters the eye through a thin membrane called the cornea.It is the eye’s outermost layer. It is the clear, dome­shaped surface that covers the front of the eye. It plays an important role in focusing your vision.

PUPIL -> The pupil is a hole located in the centre of the iris of the eye that allows light to strike the retina. It appears black because light rays entering the pupil are either absorbed by the tissues inside the eye directly, or absorbed after diffuse reflections within the eye. The pupil regulates and controls the amount of light entering the eye.

IRIS -> It is a dark muscular diaphragm that controls the size of the pupil and thus the amount of light reaching the retina.

CILIARY MUSCLE -> The ciliary muscle is a ring of smooth muscle in the eye’s middle layer that controls accommodation for viewing objects at varying distances and regulates the flow of aqueous humour into Schlemm’s canal. It changes the shape of the lens within the eye, not the size of the pupil. 


The light-sensitive cells get activated upon illumination and generate electrical signals. These signals are sent to the brain via the optic nerves. The brain interprets these signals, and finally, processes the information so that we perceive objects as

they are.

When the light is very bright, the iris contracts the pupil to allow less light to enter
the eye. However, in dim light the iris expands the pupil to allow more light to enter
the eye. Thus, the pupil opens completely through the relaxation of the iris.

A human being has a horizontal field of view of about 150° with one eye and of about 180° with two eyes. 









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