How can diabetes affect the eye?

Your eye has a lens and an aperture (opening) at the front, which adjust to bring objects into focus on the retina at the back of the eye. The retina is made up of a delicate tissue that is sensitive to light, rather like the film in a camera.

At the centre of the retina is the macula which is a small area about the size of a pinhead. This is the most highly specialised part of the retina and it is vital because it enables you to see fine detail and read small print. The other parts of the retina give you side vision (peripheral vision). Filling the cavity of the eye in front of the retina is a clear jelly-like substance called the vitreous.

The retina is a light-sensitive tissue at the back of the eye. When light enters the eye, the retina changes the light into nerve signals. The retina then sends these signals along the optic nerve to the brain. Without a retina, the eye cannot communicate with the brain, making vision impossible.

To view an interactive lesson in the functions of the various parts of the eye,
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How does the eye "see"?

Thinking of a camera can help you understand how the eye works. macular or retinal damage.

A camera lens focuses a picture onto a film inside the camera. In our eyes the same thing happens, but the film is replaced by the retina. The retina 'makes' the pictures of the world that we see, converting the light into electrical signals that are then sent on to the brain.

The retinal cells stand next to each other, a bit like houses in a street. The main cells are the rods and cones: these are the cells that take up light and convert it into electrical messages, which are then sent onto the brain.

These cells receive their oxygen and other nutrients from tiny blood vessels nearby. These blood vessels are like pipes which pass nearby the cells; imagine a largish pipe passing past your house, containing blood. The walls of these pipes/blood vessels are very thin, and so nutrients can pass through them. These nutrients are the 'food' for the cells.

As you read on, you will understand the major role played by a part of the retina called the "macula"

The macula is the most sensitive part of the retina. It makes out the fine details of the things we look at, peoples' faces, bus numbers, reading and writing, and everything lese we see.

If the macula is damaged all these things you see in fine detail are misty. The picture is still there but you cannot make out any of the detail.

A healthy retina will produce a clear image, like a normal film in a camera. But in macular damage the image will not be clear.

For example if the film was scratched in the middle, the 'scratch' would show up in the middle of the photograph like a black mark or blot of ink. This is similar to damage caused by macular disease such as diabetic maculopathy.

Diabetes causes damage to the blood vessels that nourish the retina, the seeing part at the back of the eye.