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About the eye

There are two main areas of the eye. The front of the eye is the area you can see. The back of the eye is the area behind. It is often called the eyeball.

The eyeball

The outside of the eyeball is a fibrous white layer called the sclera. Inside this is a layer rich in blood vessels. This layer is called the uvea, and is where eye cancers often start. The third, innermost layer of the eyeball contains the retina. The retina is the nerve layer of the eye. The cells of the retina react to light. They send messages to the brain through the optic nerve, making it possible for you to see.

The inside of the eyeball is filled with a clear, jelly like substance called vitreous humour.

The front of the eye

The coloured part of your eye is called the iris. In the middle of the iris is the pupil, which is the hole that lets light into your eye. The iris and the pupil are covered by a clear layer called the cornea.

Around the eye

The tissue surrounding the eye is called the orbit. It is made up of muscles and nerves. The tear glands and the eyelid are called adnexal structures. Cancers that develop in them are called adnexal cancers.

 

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The globe of the eye

There are two main areas to the eye – the front of the eye and the back, the eyeball. You can see these in the diagram below.

Diagram showing the different parts of the eye

 

The eyeball

The eyeball has three layers sandwiched together

  • The outer white fibrous layer, the sclera
  • The middle blood rich layer, the choroid
  • The inner coloured (pigmented) layer, the retina.

The inside of the eyeball is filled with a clear jelly like substance called vitreous humour. This, and the fibrous white sclera help to keep the shape of your eyeball.

The blood vessels that run through the choroid carry food and oxygen to the cells of the eye.

The retina lines the inside of the eyeball. This is the nerve layer of the eye. The cells of the retina react to light. They send messages to the brain through the optic nerve, making it possible for you to see.

 

The front of the eye

The front of the eye is the bit you can see. A thin, clear, moist membrane called the conjunctiva coats the inner surfaces of the eyelids and the outer surface of the eye.

The 3 layers of the eyeball continue round but they make up different structures in the front of the eye.

The fibrous sclera becomes clear, instead of white. This part of it is called the cornea and covers your pupil and iris.

The middle choroid layer becomes the iris and the ciliary body. The iris is the coloured part around your pupil that covers the lens of the eye. It controls how much light enters your eye.

The ciliary body lies just behind the iris. It has two functions. It is the muscle that controls the focusing of the eye. And it makes the clear fluid (aqueous humour) that fills and shapes the front of your eye.

 

The uvea

The middle layer of the eye is called the uvea. The front (anterior) uvea includes the iris and ciliary body. The back (posterior) uvea is the choroid. The uveal layer is the most common place for eye cancers to start. You may hear your doctor talk about uveal, iris, ciliary body or choroidal melanomas.

 

The tissues surrounding the eyeball (orbit)

The orbit is the tissue surrounding the eyeball. It includes

  • Muscles that allow the eyeball to move in different directions
  • Nerves attached to the eye

Cancers in this part of the eye are called orbital cancers. They are very rare.

 

Structures around the eye

Structures around the eye include the eyelids and tear glands. They are called accessory or adnexal structures. So doctors call cancers that develop in these tissues adnexal cancers.

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Updated: 24 September 2013