Keratoconus & Corneal Problems
Keratoconus & Corneal Problems

How the eye works

We need light to see what is around us and to see colour. Light bounces off the objects we look at. These reflect different amounts of light which we see as different colours.

Front of the eye

Light rays enter the front of our eye through the clear cornea and lens. It is very important that both the cornea and lens are clear as this allows the light to pass directly through the front of the eye to the retina.

The cornea and lens bend light so that it can focus on the retina at the back of our eye. This gives us a clear, precise image. The cornea focuses the light towards our retina. The lens fine tunes the focusing of this light.

Our tears form a protective layer at the front of the eye and also help to direct the light coming into our eye.

The iris, the coloured circle at the front of our eye, changes the size of the pupil which allows different amounts of light into our eye.

The pupil is the dark hole in the middle of the coloured part of our eye. The pupil gets smaller in bright conditions to let less light in, and bigger in dark conditions to let more light in.

Middle of the eye

The middle of our eye is filled with a jelly-like substance called the vitreous. The vitreous is clear and allows light to pass directly from the front to the back of our eye.

Back of the eye

The retina at the back of the eye is a light-sensitive layer which consists of rod and cone cells. These cells collect the light signals directed onto them and send them as electrical signals to the optic nerve at the back of our eye.

Rod cells are concentrated around the edge of the retina. They help us to see things that aren't directly in front of us, giving us a rough idea of what is around us. They help us with our mobility and getting around by stopping us from bumping into things. They also enable us to see things in dim light and to see movement.

Cone cells are concentrated in the centre of our retina where the light is focused by the cornea and lens. This area is called the macula.

Cone cells give us our detailed vision which we use when reading, watching TV, sewing and looking at people's faces. They are also responsible for most of our colour vision.

The optic nerve is made up of thousands of nerve fibres. These fibres pass the electrical signals along to our brain where they are processed into the image we are looking at.

How we see

Seeing can be likened to the process of taking pictures on a film with a camera which you then get developed. The retina is like a camera film which stores an image of what we are looking at. The image directed onto the retina is then sent along to the brain where it is processed, like developing a camera film. Therefore we actually "see" in our brain with the light information sent to it from our eyes. This whole process happens very quickly so that everything we see is in focus.

About corneal dystrophies

Corneal dystrophies are relatively rare eye conditions and most tend to occur in the first few decades of life. The exception is Fuchs'Dystrophy, which appears much later. Most run in families and if a corneal dystrophy is discovered in one family member, then all other adult family members should be examined. While they can lead to serious sight loss, they only account for roughly 0.5 per cent (half of one percent) of all those registered as blind and partially sighted.



The cornea is the clear outer layer covering the front of the eye. Normally it is smooth and as transparent as glass but it is also very strong. It helps the eye in two ways:

Firstly it acts as a barrier between the eye and the outside world and helps to protect the eye from injury and infection. The cornea is extremely sensitive and can detect the presence of even the smallest piece of dirt or fluff.

And secondly, it is the eye's outermost lens, controlling and focusing the entry of light into the eye. The cornea bends the incoming light onto the lens. The lens further focuses the light onto the retina at the back of the eye, which converts the light into images which are then sent to the brain.

Therefore, the cornea is vital for maintaining both the health of the eye and good, clear vision. It is normally able to cope well with minor injuries.



The name literally means "conical or cone-shaped cornea" and rarely appears until puberty or older. In keratoconus the cornea becomes stretched and thins at its centre, and the thinned part of the cornea bulges making the vision more shortsighted and irregular. As a result the vision is distorted. The stretching of the cornea tends to progress but the rate varies. Both eyes are affected but the condition may not be at the same stage in both eyes. The majority of people with keratonconus have no family history of the condition and are very unlikely to have affected children.

Treatment usually begins with the use of rigid contact lenses, although soft contact lenses or spectacles may still be suitable in the early stages. The rigid contact lenses help to provide the best possible vision but they do not affect the rate of progression of the condition. As the condition progresses good vision may be difficult to maintain and contact lens tolerance may vary.

A condition called 'hydrops' may also occur. This may result in a sudden drop in vision and is due to a break in Descemet's membrane allowing fluid to leak into the stroma of the cornea. This can be uncomfortable and cause the eye to water. It may also lead to scarring.

In at least 20 per cent of people with keratoconus, the cornea may become extremely steep, thin and irregular, or the vision can no longer be improved sufficiently with contact lenses. At this stage the cornea may need to be replaced surgically with a corneal transplant. Over 90 per cent of corneal transplants done for keratoconus continue to allow good vision at five years post-transplant