Test: Human Eye - UPSC

The retina is the inner back portion of the eye. It is composed of an enormous number of light-sensitive cells.
The lens forms an image of the visual world on the retina through the cornea.
Light-sensitive cells of the retina get activated upon illumination and generate electric signals.
Optic nerves send these electric signals to the brain, where these signals finally processed and interpreted to see an object as they are.

Light enters the eye through the cornea and from the cornea, the light passes through the pupil.
The iris, or the colored part of your eye, controls the amount of light passing through. From there, it then hits the lens.

The image will be upside down. As it passes the lens, it gets inverted.

The ciliary muscles change the focal length of the eye lens by changing its shape.

The space between the lens and the retina is called Vitreous Body and is filled with a transparent gel called Vitreous Humorous.

There is no change to the image distance in the eye when we increase the distance of an object from the eye.

To see closer or distant objects clearly, the eyes, due to their accommodation, can increase or decrease the focal length of its lens, by contraction and relaxation of ciliary muscles, so that the image is always formed at the retina.

Changes in the contraction of the ciliary muscles alter the focal distance of the eye, causing nearer or future images to come into focus on the retina; this process is known as accommodation.

The focal length of the eye lens increases when eye muscles relaxed and becomes thinner. The sharp image of the distant object is formed at the retina. This enables us to focus accurately on distant objects.

• The lens in turn focuses the light rays onto the retina, lining the back of the eye.
• The retina converts the image formed by the light rays into nerve impulses.
• The optic nerve, composed of the axons of the retina's ganglion cells, then transmits these impulses from the eye to the first visual relay in the brain.

The function of pupil is to control the amount of light entering the eye and the iris controls the pupil.