Derby Eye Surgery
Lazy Eye

What is it?

Lazy eye and squint are often assumed to be the same thing, which (though related) they are not. A lazy eye is where the vision in one eye is reduced because the visual part of a young child’s developing brain is not fully responding to the input of that eye. The alternative word for lazy eye is amblyopia.

The other eye is normal and the child will actually function as though he or she is seeing quite normally, which can make lazy eye difficult to diagnose. If diagnosed early enough a lazy eye can be treated. After a certain age this treatment does not work. Most people can function quite normally in spite of a lazy eye, things like reading and driving not being affected. That said it’s always better to have both eyes seeing as best they can so it is well worth treating lazy eye if it is found early enough. Because of this, all children in Derby aged three to four years old are offered screening for squint and lazy eye.

What causes it?

The two most common causes of this are firstly when one eye is constantly pointing the wrong way (squint); and secondly when one eye is more blurred due to being more long or short sighted than the other eye. Being long or short sighted is known as having a refractive error (see refractive errors). When one eye has a greater refractive error than the other, this is called anisometropia.

Quite often the two (squint and anisometropia) are combined making the eye particularly lazy.

If a child develops a greater refractive error on one side, the developing visual brain “ignores” that eye. This occurs because the image is more blurred due to the refractive error and the normal connections from that eye in the brain don’t develop properly. 
In a child with a squint a different but related process occurs in the brain. By doing this the child avoids double vision. If an adult develops a squint, their mature brain cannot do this and they suffer from double vision. In a child with a combination of a squint and greater refractive error in that eye, both processes occur in the brain at the same time and the eye is rendered very lazy.

If the lazy eye is not treated before a certain age the brain changes become permanent and that eye will always have reduced vision, even if glasses are used. 

How is lazy eye treated?

Treatment of lazy eye depends on what the cause is. If the only problem is that one eye is a lot more long or short sighted than the other eye (anisometropia), then giving the child glasses will be the first step. Over a period of time the visual brain will start to use the lazy eye, now that this eye is not more blurred than the other eye, and the correct connections within the visual brain form. In short, the eye starts seeing better. 

More often than not this is all that is required. Provided the vision in the lazy eye improves to a satisfactory level nothing else is done. However the glasses will need to be worn all the time until the child is much older (11 or 12), otherwise the lazy eye may recur. After that it’s not as vital to wear the glasses all the time but many continue to do so.

If the vision does not improve to a satisfactory level with the use of glasses alone, treatment involves forcing the visual brain to use the weaker eye by somehow reducing the input from the better eye. The traditional method is by placing a patch over the better eye for all or part of the day. Generally the better eye is patched for several hours a day over a period of four to six months. However the requirement for patching varies from person to person. For example, very lazy eyes usually require longer periods of patching. An alternative to patching is to blur the better eye by putting a drop in that dilates the pupil. This drop is called atropine and has to be put in once a day. Some experts think this is not as effective as patching, but others think that it is. Whatever method of treatment is used, the child will need to be seen regularly (every few months) until he or she has responded to treatment and has reached an age where the vision is stable (about seven years old).

If a squint (one eye pointing the wrong way- see squint) is the cause of the lazy eye, then the treatment is the same but often takes longer. Many children with a squint also have a higher refractive error (usually more longsighted) in the squinting eye. This combination of squint and difference in refractive error will often make the eye very lazy. These children will need glasses in the same way to help treat the lazy eye and more often than not require prolonged patching treatment. They usually also need glasses to help control the squint, so the glasses in effect are doing two jobs at the same time.

Who treats it?

A number of health professionals are involved and it can be confusing.
An orthoptist is someone who has been trained to assess lazy eyes and squints. They also treat lazy eyes and monitor the progress of this treatment. When a child is having treatment for lazy eye, most of the time they will be seen by an orthoptist. Initially they will also have a glasses test (refraction) which is usually performed by an optometrist (optician). Glasses tests are performed at least once a year. Children with squints very rarely can have retinal or neurological disease as a cause of the squint. Because of this these children are always seen by an eye surgeon (ophthalmologist) at an early stage to rule this out.

Childrens eye problems

Lazy Eye
Refractive Errors
Sticky Eye


Derby Eye Surgery

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 Roger Holden Eye Surgeon
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