What Each Part of the eye Actually Does

The Eye is a complex sensory organ. It is designed to optimize vision under conditions of varying lighting. The basic elements are similar to those of an average photography camera. The primary function is to focus light. To see, light rays must be bent or "refracted" to meet at a single point through the cornea, the clear window at the front of the eye that provides most of the focusing power. The transparent dome cornea is a firm covering and is susceptible to dryness and abrasion injuries.

The iris is the coloured portion behind the cornea. The colour is a function of the amount of pigment within the iris. The iris contains muscles that open and close its central opening called the pupil in response to decreases and increases in light exposure. Light then travels through the lens, where it is fine-tuned to focus properly on the retina, the nerve layer that lines the back of the eye and connects to the brain. The retina acts like the film in a camera, and clear vision is achieved only if light from an object is precisely focused onto it. If the light focuses either in front of or behind the retina, the image you see is blurred. A refractive error means that the shape of eye structures does not properly bend the light for focusing.

Having 20/20 vision means seeing at 20 feet what a normal person sees at 20 feet. However, if vision is measured at 20/40, it means a person has to walk up to 20 feet to see the same size letter that someone with 20/20 vision could see at 40 feet. People whose best- corrected visual acuity (what they see using glasses or contact lenses) is less than 20/200 in the better eye are considered legally blind, even though they still have enough vision to get around.