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Eye terminology

Some of these words might sound familiar, but you might n0t be sure of their meaning.  Here are some helpful shortcuts to help your understanding of the eye and how it works.  As always, please talk to our staff if you are unsure about anything we might have said.

The cornea is a clear membrane at the very front of your eye. It is somewhat "pointed", and this can be felt through the closed eyelid. The cornea is an important structure for focussing light from the environment onto the retina.

The iris is the coloured part of the eye - blue, brown, hazel etc. Like the shutter in a camera, it regulates the amount of light entering the eye from the environment. In bright light, a small circular muscle contracts and makes the pupil (the black part in the centre) smaller - letting in less light. In the dark, this muscle relaxes, and more light can enter.

The lens sits just behind the iris, near the front of the eye. It is held in place with very fine suspensory ligaments, and is contained in a capsule or "bag". Running in a circle around the eye (under the "white" part) is a muscle that adjusts tension on the ligaments and capsule, allowing change in focus (especially up close). The lens stiffens after about age 40, and becomes less able to change shape. This is why reading can become difficult without the aid of reading glasses.

The vitreous is the "jelly" of the eye. It occupies most of the space in your eyeball, and is (mostly) completely clear. In some patients it separates from the retina, and this can cause retinal breaks - leading to a very serious condition called retinal detachment.

The retina is the innermost of the eye's three "coats". It is a very highly organised arrangement of specially adapted sensory and relay nerves, and its function is to detect light from the environment and turn it into electrical signals which are then relayed to the brain. These electrical impulses are then interpreted by our brains to create our experience of vision.

There are no pain detectors in the retina, which is why retinal tears happen without any symptoms.

The macula is at the very back of the eye, and it is the part we use for central vision i.e. fine detail and reading. In contrast, the remainder of the retina is used for peripheral, or "side" vision. Both are very important.

The choroid is a layer of blood vessels and supporting structures that lie underneath the retina - it is the middle layer of the eye's three "coats". Many important causes of vision loss arise in the choroid - the commonest of these is age-related macular degeneration, but it is also the site of inflammatory conditions.

The sclera probably known by most people as the "white" of your eye, and is the outermost of the eye's three "coats". It is a very tough meshwork of many collagen fibres (a type of structural protein), and its main function is to support the internal eye structures and protect them from the outside environment.

Many people are surprised to learn that the eye is actually part of your brain. The optic nerve is the "cable" that connects the eye to the rest of the brain, and is therefore very important for relaying visual information about the world.


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