### Theory:

The cornea, a transparent layer, bends the light rays through the pupil located at the centre of the Iris. The adjusted light travels through the eye lens.

The eye lens is convex in nature. So, the light rays from the objects are converged, and a real and inverted image is formed on the retina. Then, the retina passes the received real and inverted image to the brain through optical nerves. Finally, the brain senses it as an erect image.

Structure of the human eye

Power of Accommodation:
The power of the eye's accommodation is the capability of the eye lens to focus nearby and distant objects. This is attained by modifying the focal length of the eye lens with the help of ciliary muscles.
The eye lens is comprised of a flexible, jelly-like material. Whenever the ciliary muscle relaxes, and contracts, the curvature and hence the focal length of the eye lens can be changed.
The ciliary muscle relaxes when we see distant objects and causes the eye lens to thinner. This results in an increase in the focal length of the eye lens. Hence, the object in the distant location can be clearly seen. On the other hand, when we see a closer object, the focal length of the eye lens is decreased by the contraction of the ciliary muscle. Thus, the image of the closer object is formed on the retina.
Persistence of vision:
If the time interval between two successive light pulses is less than $$1.16\ seconds$$, the human eye cannot distinguish them separately. It is called persistence of vision.

The far point and near the point of the human eye:
The minimum distance needed to see the objects distinctly without strain is known as the least distance of distinct vision. It is called a near point of the eye. It is $$25\ cm$$ for the normal human eye.

The eye's far point is the maximum distance at which the eye can clearly see objects. The normal eye sees infinity.