Human Eye – 10th Board

A human eye is a complex organ that is responsible for the vision. It creates images of objects around us and help brain see that with clarity.

An eyeball is a nearly spherical structure in which lies the image formation system of the eye. It consists of cornea, iris, pupil, eye-lens, ciliary muscles, retina etc. among others. Its diameter is 2.5 cm.

The cornea is the outermost transparent layer of the eye. It forms the bulge of the eye. It bends most of the light falling on it towards the lens.

The small circular opening behind the cornea through which light passes is pupil. It controls the amount of light that reaches the eye-lens.

Iris is a dark muscular diaphragm that controls the size of the pupil. It thus controls amount of the light passing through pupil. It is also responsible for the color of the eye.

An eye-lens is a biconvex lens that provides fine bending to the light rays. It helps creation of distinct images at retina. The image is real and inverted. Eye-lens changes its focal length to focus objects at varying distances.

Ciliary muscles hold the eye-lens in place. It changes the shape of eye-lens while seeing objects at varying places. It does so by relaxing and contracting.

A retina is the light sensitive part of the eye. When real images form here, it generates electric signals. These signals are sent to brain for image perception.

Optic nerves carry the electric signals generated by the retina to the brain. Brain interprets the signals and help us perceive the objects.

The near point of an eye is the closest distance at which an object can be seen clearly. This is also known as least distance of distinct vision. For a normal adult eye, near point is typically 25 centimeters.

The farthest distance at which an eye can see the objects clearly is known as the far point. For a normal adult eye, the far point extends to infinity.

Range of normal vision of an adult eye span from 20 centimeters (near point) to infinity (far point.