Vision deals with the science of how the eye “sees”. When light is reflected off an object, the lens of the eye either thickens or thins to make it come into focus. When the object is near, the lens of the eye thickens to bring it into focus; and it thins to enable us to focus on objects farther away.
The image is then recorded by photoreceptors in the retina (located at the back of the eye), then transmitted to the brain via the optic nerve to be appreciated.
The amount of light entering the eyes is regulated by the pupil and the iris. The iris is a contractile structure, consisting mainly of two groups of muscle (a circular group called the sphincter pupillae, and a radial group called the dilator pupillae), surrounding the pupil. Light enters the eye through the pupil, and the iris regulates the amount of light by controlling the size of the pupil. In bright light, the circular iris sphincter muscle contracts and the radial dilator relaxes, to reduce the size of the pupil. This reduces the light coming into the eye, thus protecting the retina from damage.
To see better in low light conditions, the circular iris sphincter muscle relaxes and the radial dilator contracts, to increase the size of the pupil. Thus allowing more light to enter the eye.
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