The Eye and Defects

The human eye is an optical system that focuses light onto the retina.

The **cornea** provides a large part of the eye's refraction.

The eye lens fine-tunes the focus of incoming light.

The **iris controls the size of the pupil** and therefore regulates how much light enters the eye.

The retina contains light-sensitive receptor cells. A focused image forms on the retina and is converted into nerve signals.

**Accommodation** is the process by which the eye changes the shape of its lens to focus on objects at different distances.

A myopic eye focuses distant objects in front of the retina. It can be corrected using a concave/diverging lens.

A hypermetropic eye has difficulty focusing nearby objects, with the uncorrected focus tending to fall behind the retina. It can be corrected using a convex/converging lens.

With age, the eye lens becomes less flexible and accommodation becomes weaker. This can make near focusing difficult.