What Is Lazy Eye? What Is Amblyopia? What Causes Lazy Eye Or Amblyopia?

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Main Category: Eye Health / Blindness
Also Included In: Pediatrics / Children's Health
Article Date: 19 Sep 2009 - 0:00 PST

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Lazy eye is also known as Amblyopia. Lazy eye is an early childhood condition where a child's eyesight in one eye does not develop as it should. The problem is usually in just one eye, but can sometimes affect both of them.

When a patient has amblyopia the brain focuses on one eye more than the other, virtually ignoring the lazy eye. If that eye is not stimulated properly the visual brain cells do not mature normally. In the USA and UK amblyopia affects approximately 2% to 3% of all children. It is the most common cause of partial or total blindness in one eye (monocular blindness) in the USA.

The term lazy eye is inaccurate, because the eye is not lazy. In fact, it would probably be more accurate to say lazy brain, because it is a developmental problem in the brain, not an organic problem in the eye.

What are the symptoms of lazy eye?

A child with lazy eye will not be able to focus properly with one of their eyes. The other eye will make up for the problem, so much so that the affected eye suffers as a result. The eye with impaired vision (amblyopia) will not receive clear images; the brain won't receive clear data, and will eventually start to ignore it.

In many cases the brain and the good eye make up for the shortfall so well that the child does not notice he/she has a problem. That is why lazy eye is often first detected after a routine eye test.

The signs and symptoms of a lazy eye may include:

• Blurred vision
• Double vision
• Poor depth perception (of vision)
• Eyes do not appear to work together
• A squint (either upwards, downwards, outwards, or inwards)

It is important for a child to have a vision check. In most countries the first eye exam occurs at the age of 3 to 5 years. It is especially important to have an early eye check if there is a family history of crossed eyes, childhood cataracts or other eye conditions. Parents who see their child's eye wandering after they are a few weeks old should tell their doctor.

What causes lazy eye?

Anything that causes a child's eyes to cross or turn outward, or something that blurs their vision can provoke lazy eye. Below are examples of some possible causes:

• An imbalance in the muscles that position the eye - strabismus - causing them to cross or turn out. The muscle imbalance undermines the two eyes' ability to track objects together (move in harmony with each other, in a synchronized way, to be aligned). Strabismus may be inherited; it could be the result of long- or short-sightedness, a viral illness, or an injury.


• Anisometropic amblyopia - a refractive error occurs due to myopia (short-sightedness), hypermetropia (long-sightedness), or astigmatism (the surface of the lens is uneven, causing blurred vision). A refractive error means light changes direction after going through the lens differently in each eye. A child with anisometropic amblyopia will be more long-sighted or short-sighted in one eye than the other, resulting in amblyopia developing in the eye that is affected more.


• Stimulus deprivation amblyopia - this is the most uncommon form of amblyopia. One eye (or sometimes both) is prevented from seeing, and becomes lazy. This could be due to:
  
  
  • A corneal ulcer, a scar, or some other eye disease
  • A congenital cataract (baby is born with clouding of the lens)
  • Ptosis (droopy eye lid)
  • Glaucoma
  • Eye injury
  • Eye surgery

How is lazy eye diagnosed?

Vision problems, any level of blindness in one eye - amblyopia - ideally, needs to be detected before the child is six years old. Diagnosis can sometimes be made a long time after the onset of problems, especially if the child is unaware that there is something wrong with his/her vision.

Routine eye examination

In developed nations children have their first eye examination between the ages of 3 and 5 years, or before they start school. This means that most cases of amblyopia are diagnosed, and subsequently treated in developed nations.

If the ophthalmologists suspects the child has lazy eye further tests will be carried out before a diagnosis is reached. Each eye is tested separately to determine whether there is any short- or long-sightedness, and how serious it is. The child will also be carefully tested to determine whether there is a squint.

The eye test will also determine whether the child has astigmatism or any other abnormality.

What are the treatment options for lazy eye?

An ophthalmologist and an orthoptist usually treat children with lazy eye. Treatment tends to be more effective the younger the child is. After a child is eight years old the likelihood of effective treatment drops significantly. However, evidence that the brain regions responsible for vision that are capable of adapting in adults offers new hope for those with lazy eye.

There are two approaches to lazy eye treatment:

Treating an underlying eye problem.
Getting the affected eye to work so that vision can develop.

Treatment for underlying eye problems

Many children who have unequal vision - anisometropia - do not know they have an eye problem because the good eye and the brain compensate for the shortfall. Sadly, the bad eye progressively suffers and amblyopia (blindness) develops.

• Glasses - a child with myopia (short-sightedness) or hypermetropia (long-sightedness) will be prescribed glasses. The child will have to wear them all the time so that the specialist can monitor how effective they are on improving amblyopia (vision problems on the lazy eye). Glasses may also get rid of a squint. Sometimes, glasses can solve the amblyopia and no more treatment is required. It is not uncommon for children to complain that their vision is better when they don't wear the glasses. They need to be encouraged to wear them for the treatment to be effective.


• Cataracts - cataracts can be surgically removed with either local or general anesthetic.


• Ptosis (droopy eye lid) - the usual treatment for this is surgery.

Getting the lazy eye to work

• Occulation (using a patch) - A patch is placed over the good eye so that the lazy eye has to work. As the brain is only getting data from that eye it won't ignore it. A patch won't get rid of a squint, but it will improve vision in the lazy eye.
  
  The length of treatment depends on many factors, including the child's age, the severity of their problem, and how much they adhere to the specialist's instructions. The patch is usually worn for a few hours each day. A child should be encouraged to do close-up activities while wearing the patch, such as reading, coloring or schoolwork. A child with amblyopia does not have to wear a patch all day; three to four hours daily for a total of twelve weeks is all that is usually needed to improve vision, say researchers from City University, London, England, and McGill University, Montreal, Canada.
  
  Encouraging the child to wear the patch when they are told to is important. If the child is old enough, explaining why the patch is so important helps. For some children, having to wear a patch is unpleasant, irritating and embarrassing.


• Atropine eye drops - These may be used to blur vision on the unaffected eye. Atropine dilates the pupil, resulting in blurring when looking at things close up - this makes the lazy eye work more. Atropine is usually less conspicuous and awkward for the child, compared to the patch, and can be just as effective. Children who cannot tolerate wearing a patch may be prescribed eye drops instead.
  
  Atropine may have the following rare side effects:
  
  Irritation in the eye
  Reddening of the skin
  Headaches
  


• Vision exercises - this involves different exercises and games aimed at improving vision development in the child's affected eye. Experts say this is helpful for older children. Vision exercises may be done in combination with other treatments.

Sometimes eye surgery is performed to improve the appearance of a squint, resulting in better alignment of the eyes. This will not improve vision.

What are the complications of lazy eye?

Blindness - if untreated, the patient may eventually lose all vision in the affected eye. This vision loss is usually permanent. According to the National Eye Institute, lazy eye is the most common cause of single-eye vision impairment in young and middle-aged adults in the USA.

Squint - strabismus, where the eyes are not properly aligned, can become a permanent feature.

Central vision - if amblyopia is not treated during childhood the patient's central vision may not develop correctly. The problem may affect his/her ability to do certain tasks.

Written by Christian Nordqvist
Copyright: Medical News Today
Not to be reproduced without permission of Medical News Today