The light rays coming from the object kept in front of us enter through the cornea of the eye, pass through the pupil of the eye and fall on the eye- lens. The eye- lens, so it converges the light rays and produces a real and inverted image of the object on the retina. (Actually, the outer surface of cornea also acts as a convex lens due to which Corenea converges most of the light rays entering the eye.

Only the final convergence of light rays is done by the eye- lens to focus the image of an object exactly on the retina. The image formed on the retina is conveyed to the brain 🧠 by the optic nerve and gives rise to the sensation of vision. Actually, the retina has a large number of light sensitive cells. 

When the image falls on the retina signals to the brat through the optic nerve and gives rise to the sensation of vision. Although the image formed on the retina is inverted, our mind interprets the image as that of an erect object.

As far as physics is concerned, the eye consists of a convex lens (called eye- lens) and a screen (called retina). The eye- lens form a real image of the forms a real image object on the retina of the eye and we are able to see the objects. The human eye is like a camera. In the eye, a convex lens (called eye- lens) forms a real and inverted image of an object on the light- sensitive screen called retina whereas in a camera, the convex lens (called camera- lens) form a real and inverted image of an object on the light sensitive photographic film.

The Function of Iris and Pupil

The iris controls the amount of light entering the eyes. The iris automatically adjusts the size of the pupil according to the intensity of light received by the eye. If the amount of light received by the eye is large (as durning the time), then iris contracts the pupil (makes the pupil small) and reduces  the amount of light entering the eye. On the other hand, if the amount of light received by the eye is small (as in dark or during night), the iris expands the pupil(makes the pupil large) do that more light may enter the eyes. 

Thus, the iris regulates (or controls) the amount of light entering the eye by changing the size of the pupil. The iris makes the pupil 'expand' or contract according to the intensity of light around the eye.If the intensity of the outside light is low, then the pupil expands to allow more light to enter the eye. On the other hand, if outside intensity of high, then the pupil contracts so that less light enters the eye.

It should be noted that the adjustment of the size of the pupil takes some time. For example, when we go from a bright light to a darkened cinema hall, at first we cannot see our surroundings clearly.After a short time our vision improves , and we can see the persons sitting around us. 

This is due to the fact that in bright sunlight the pupil of our eye is small. So, when we enter the darknesned cinema hall, very little light enters our eye and we cannot see properly. After a short time, the pupil of our eye expands and becomes large.

More light then enters our and we can see clearly. On the other hand, if we go from a dark room into bring sunlight or switch on a bright lamp, then we feel the glare in our eyes. This is due to the fact that in a dark room, the pupil of our eye is large. So, when we go out from a dark room into bright sunlight or switch on a bright lamps, a large amount of light enters our eyes and we go feel the glare. Gradually, the pupil of our eye contracts. Less light then enters our eye and we can see clearly. In this way, the iris also protects eyes from the glare of bright lights.