long-sightedness

long-sightedness is more common, although usually milder than short-sightedness. long-sightedness is associated with difficulties in seeing objects that are close by. Glasses need to be worn for close work, such as reading and writing.

Short-sightedness

Short-sightedness is usually indicated by the child’s need to get very close up to objects. Children who sit close to the television set, however, do not necessarily do so because they are short-sighted. They may just enjoy being close to action. Short-sightedness is corrected by glasses, which usually need to be worn as much as possible. Holes can be drilled in the parts of the glasses that lie just behind the ears, and a broad elasticised band can be attached which wraps around the back of the head, keeping the glasses in place. Glasses with curled wire ends that fit around the ears may be sufficient. If the child takes the glasses off, you should not make a fuss, but say firmly ‘NO’ and replace them. Some children will not tolerate glasses except when at school. In this case, it may be best to have the teacher keep the glasses, which can be put on on arrival and taken off before going home.

Squint

Around 20% of children with Down’s syndrome have a squint. A squint is when the eyes are pointing in slightly different directions. Squints can be intermittent especially when they first appear; others are constant. In some cases the child alternates between squinting with the right eye and the left eye; in others, the child squints constantly with the same eye. When one eye moves out of alignment the brain receives two separate images so the one from the squinting eye is suppressed. The vision in a constantly squinting eye tends to be reduced.

Many children squint because they are long-sighted or short-sighted and consequently need glasses. Many children with a convergent squint, where one eye turns inwards towards the nose, are long-sighted (hypermetropic) and often, if such a child is given glasses to correct this the squint can become less noticeable or even disappear completely while the child is wearing the glasses. Children who are short-sighted, or who are likely to become shortsighted when they grow older, may have a tendency for one eye to drift outwards which can be controlled.

If any child is suspected of having a squint or any visual problem, it is important to arrange referral to someone who can establish a diagnosis and arrange treatment. Usually, children see an orthoptist, who always works closely with an ophthalmologist and possibly an optometrist. Often it is more difficult to recognise a squint in children with Down’s syndrome because of the distinctive appearance of the eyelids.

PEOPLE WHO SPECIALISE IN EYE CONDITIONS

• An ORTHOPTIST is specially trained in the assessment of vision in people of all ages and all abilities, the recognition of squints and disorders of eye movements and the treatment of squints and related disorders.

• An OPHTHALMOLOGIST is a doctor specialising in eye conditions.

• An OPTOMETRIST is trained to test for glasses and other aspects of visual function and to recognise ocular abnormalities. They are also able to dispense glasses.

• A DISPENSING OPTICIAN is trained to fit spectacle frames and arrange to have these made up with the appropriate measurements and lenses for individual people.

Treatment of Squints

Firstly, the child must be carefully examined to check the health of the eyes and to determine whether glasses are needed. This is usually done by putting drops into the eyes. These dilate and fix the pupil of the eye and make it possible to test accurately for glasses and examine the back of the eye with a light with only minimal co-operation from the child. Different drops are used in different clinics. Sometimes they may contain a substance called atropine. In the past some people were worried that atropine might have adverse effects for people with Down's syndrome. In fact there is no evidence whatever of any harm. The only difference is that if atropine is used the pupil may stay dilated for longer than is usual.

The second aspect of treatment is to make sure that the child has equally good vision in both eyes. An experienced orthoptist will be able to establish this and treat younger children who have reduced vision in one eye. This is often done by covering the eye which can see well for a period of time each day to improve the vision in the squinting eye. The orthoptist aims to produce equal vision in both eyes so that the child is able to use either eye to fix on a test target picture.

Thirdly, if the child has a noticeable and unsightly squint, even when wearing glasses, then surgery can be arranged to correct this. At operation the position of the small muscles on the outside of the eye is adjusted so that they pull the eye into a straighter position.

Nystagmus

About 10% of children with Down’s syndrome have nystagmus. Nystagmus is a condition in which the eyes make small, involuntary, jerky movements. Often these movements are more noticeable when the child is looking sideways. Sometimes there is a position of gaze where the movements are considerably reduced. If this is the case, the child might adopt a compensatory head posture which allows the eyes to be in a position in which the nystagmus movements are minimised. If this happens the child should not be discouraged from adopting the head posture as this is likely to be the position where the vision is at its best. The vision is often better for near than distance. Children with nystagmus often prefer to hold books very close as this improves their vision and they should be allowed to do this.

Cataracts

A cataract is when part or all of the lens of the eye has become cloudy. If the affected area is small it is possible to see round it, through the clear part of the lens. This kind of cataract does not cause a significant problem and is relatively common in people with Down’s
syndrome. A denser opacity of most of the centre of the lens is fortunately much less common as it causes a marked reduction in vision. Less than 1% of children with Down syndrome have a dense cataract.

These can be treated by removing the lens of the eye under general anaesthetic. As this leaves the eye unfocused, older people can have a lens implant at the time of the operation. Children often have an operation which makes it possible to have a lens implant inserted at a subsequent operation when the eye has reached adult size. If a lens implant is not inserted, the eye needs to be focused either by wearing thick glasses or contact lenses. Cataracts can be present at birth or develop later. They would be discovered at a routine check.

Keratoconus

This condition of the cornea (the clear structure covering the front of the eye) is more common in people with Down’s syndrome but is still relatively rare. The cornea, instead of being the normal curved shape, becomes conical. During the early stages this makes the person short-sighted, often with marked astigmatism making the vision distorted. Many cases do not progress any further than this stage. Other cases go on to develop scarring in the centre of the cornea. A small number of those affected develop sufficient thinning of the centre of the cornea to make them require a corneal graft. This is carried out under general anaesthetic.
After a corneal graft the eye is vulnerable until it is completely healed. This can present some problems in people with Down’s syndrome as the patient has to be discouraged from touching the eye.
The condition is extremely rare in childhood, may start to develop in adolescence and ultimately affects 10 – 15% of adults though for many the effects will not be serious. Although rare this is one reason why it is very important for people with Down’s syndrome to have regular eye checks throughout the teenage years and beyond.