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Eye Conditions

How the Eye Works

The eye is like a camera, focusing light and relaying the image to the brain. The brain then processes this information into the "pictures" we see.
The outer layer of the eyeball is made up of the sclera and cornea. The sclera is a thin, yet tough, protective shell which is the "white of the eye." The conjunctiva is the delicate tissue that lines the eyelids and covers the exposed surfaces of the sclera The transparent front portion is called the cornea. The cornea allows light to enter the eye and, with the lens focuses light on to the retina. If the focusing is not perfect, then the result is blurry vision. Imperfections in the focusing (or refraction) of light rays are called refractive errors. The most common refractive errors are myopia, hypermetropia, and astigmatism.
Behind the cornea is the coloured iris. The pigment in the iris determines the colour of your eyes. The pupil is the black hole in the centre of the iris, controlling the amount of light entering the eye. In this way it acts like the diaphragm in a camera. In bright conditions, such as outdoors on a bright, sunny day, the iris constricts the pupil and makes it smaller. This limits the amount of light that passes through the pupil to the retina at the back of the eye. In darker conditions the iris dilates the pupil so that more light can enter the eye.
The lens is behind the iris and focuses the image onto the retina. Light travels from the lens to the retina through the vitreous, a clear gel which holds the eye in shape.
The retina is a thin, transparent membrane that coats the back of the eye. It is similar to the film in a camera.  Special cells known as cones pick up the light. The retina sends over one million nerves through the optic nerve to the brain. These nerve fibres transmit signals to the visual part of the brain, which processes them into a "picture," or visual image.
At the centre of the retina is the macula. The macula is the most important part of the retina. It is the part that 'sees' what is at the centre of your vision. The rest of the retina is responsible for the areas you see less clearly, in the periphery of your vision, or out of the corner of your eye.
The outer coating of the eye is "floppy" like a beach ball. A clear watery fluid, aqueous, is produced inside the eye by the pigmented cells surrounding the lens (the ciliary body). This fluid provides the necessary pressure to help maintain the shape of the eye. We call this pressure the intraocular pressure (IOP). It also nourishes the cornea and the lens, providing them with oxygen and vital nutrients.
The eye is moved by a series of six muscles known as extraocular muscles.

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Journey through the human eye

How does vision work?