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What is Anisometropic Amblyopia? - (Lazy Eye)

The term ‘lazy eye’ is used to mean different things. Some people think that it means a squint, some people think it means that the vision in one eye is lazy and some people think it means a droopy eyelid.

Unfortunately, there is no easy name for anisometropic amblyopia, although it does fall into one of the ‘lazy eye’ groups.

In this condition, the vision in one eye is poor, but this is not caused by a squint.

In anisometropic amblyopia, the two eyes need different spectacle corrections – this is called ‘anisometropia’. As the two eyes are unable to focus differently, the brain will naturally focus with the eye that needs the weaker spectacle correction and sees better. So the other eye – the one that needs the stronger spectacle correction – is out of focus all the time. This means that the picture on the retina is blurred and it interferes with the clear picture in the other eye. In a child, the brain quickly learns to cut out the blurred picture
and concentrate on the clear one. The blurred picture is ignored by the brain, leading to under-use of that eye and
the vision becomes poorer or ‘lazy’. This ‘laziness’ is called ‘amblyopia’.

How can it be found?

The eye that has become lazy looks completely normal and does not squint. The eye with the better vision will be
depended on and so the child can function perfectly well. This means that this type of lazy eye can be very difficult to detect without an eye test.

This is one of the main reasons why there is a city-wide eye screening service in Birmingham. Every child is offered an eye test while they are in their Reception year at school. At this age, a child is old enough to do a thorough and
accurate eye test, but still young enough for problems to be treated. Children’s eyes develop until they are 7 or 8 years old and any treatment must be done before that age for it to be effective.

How can it be treated?

The treatment of anisometropic amblyopia is straightforward – correct the underlying cause – the anisometropia, by prescribing appropriate glasses.

If your child is found to have poor vision in one eye, they will be referred to the Paediatric Eye Service. A test for glasses will be done by an Optometrist, after the child has had drops put in their eyes.

The drops make the pupils big and paralyse the eyes’ focussing, giving a more accurate result to the test. The glasses that are prescribed will need to be worn full-time as the eye and brain need to be stimulated.

There is usually a good improvement in the vision at the first review (16 – 18 weeks) and a more gradual improvement after that.

Although the vision improves, this does not mean the glasses will need changing at this point. This is because the wearing of the glasses is overcoming the effects of the underlying anisometropia, but not changing the anisometropia itself. Paediatric Eye Service This difference between the two eyes is something that you are born with and it stays with you throughout your life. So although the overall strength of the glasses is likely to change
as the child gets older, the difference in strength between the two eyes will stay.

If at any stage the vision does not seem to be improving or if the improvement is very slow, the Orthoptist may prescribe some patching. In this case, a patch is given, to be worn over the better eye for a given amount of time. This further stimulates use of the vision in the poorer eye. While the vision is improving, the orthoptist will review the child regularly – usually every two months.

Will the glasses be permanent?

Generally speaking, the child will need to wear their glasses full-time until the vision has completed its development – usually between the ages of 7 and 8 years. After this, the situation will be reviewed, taking into account the strength of the glasses and the child’s vision with and without them. At this stage, it may be possible for the child to wear the glasses just for close-work or even discard them altogether. This is obviously only done under careful supervision by the Orthoptist and only when it is certain that the vision is stable and will not deteriorate.