Amblyopia

Also known as lazy eye

Amblyopia refers to reduced vision in an eye that in other ways seems normal. It is the most common cause of poor vision in children and about 1 in 25 children develop some degree of amblyopia.

It occurs when the part of the brain that deals with vision fails to develop normally. Sometimes the term lazy eye is also used to mean a wandering eye, but this is a different condition to amblyopia.

Causes

Through the first seven or eight years of a child's life, the vision centre in the brain is constantly developing. If vision is interfered with in any way then the brain will start to prefer one eye over the other. This will cause the vision in the other eye to suffer. To reverse the process and bring the vision back in the poor eye, it is necessary to make the brain use this eye again. 

Possible causes of amblyopia include

  • strabismus (turning eye or squint)
  • abnormal focus (refractive errors)
  • cloudiness in one eye leading to visual deprivation.

Strabismus – turning eye or squint

Strabismus is a visual problem in which the eyes do not look in the same direction. One eye may look straight ahead, while the other eye turns inward, outward, upward, or downward.

Strabismus can cause amblyopia, eg, if there is an in-turning of the eye, and it is always the same eye that turns in, then this eye will become amblyopic. If the child swaps back and forth quite freely and both eyes are being used equally then there will be no amblyopia. This is called alternation.

When amblyopia from a turned eye is being treated then the development of alternation is a sign that the treatment is successful, ie, if the other eye starts to turn it means the child is now using the previously bad eye.

Abnormal focus

Any problem that causes vision to be blurry during childhood can cause amblyopia. The most common problems are: poor focusing due to myopia (short-sightedness), hyperopia (long-sightedness) or astigmatism (irregularity of the focus).

Visual deprivation

Anything that interrupts the passage of light into the eye, such as a scar on the surface, a cataract (an opaque lens in the eye) or a very droopy eyelid can lead to amblyopia.

Treatment

With regular exercise, the vision in the affected eye will improve. Therefore, amblyopia treatment relies on the child using the poorer eye. Patching or covering the good eye is the most common way of encouraging use of the poorer eye.

Patching can be done full-time, with the patch worn all day every day for a set period, after which the vision is checked again. Or it can be done part-time for a certain number of hours a day. It is easier to treat amblyopia successfully if the treatment is started while the child is young. Beyond the age of five-and-a-half years it becomes increasingly difficult to reverse amblyopia. Beyond seven years it is usually impossible.

Tips on patching

Patching is hard work for both parents and children. Most children, even in infancy, object to the patch or sometimes simply fall asleep when it is put on.

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  1. It gets easier. Getting started is the hardest part of patching. Most children will learn to tolerate patching over time, particularly if the vision starts to improve in the bad eye.
  2. King/Queen for the Day. It may be helpful to start patching on a weekend when there may be more adult support available. Focus your attention on that child. Filling the day with special privileges and attention may distract the child from some of the initial difficulties.
  3. Positive reinforcement. Rewards, or linking patching with activities the child enjoys (eg, watching videos) is usually more successful than negative reinforcement or punishment. Try to avoid a battle of wills between child and parent. If this occurs, try a lower level of patching to regain co-operation and use positive reinforcement to build it up again.
  4. Be creative. Putting pictures or bows on the patch or even creating games (eg, pirates) can be helpful.
  5. For young children. There are strategies you can use to keep a patch on such as hand socks to make it more difficult for a child to peel the patch off. Another option is inflatable water wings, when placed around the elbows can prevent a child from bending his arms enough to reach the patch on his face, whilst still allowing him to use his arms normally for play.
  6. Patching can be done at home or at kindergarten or school. Patching at home lessens the chance of embarrassment and teasing, but if you feel the supervision and distraction is greater at Day Care or kindergarten then it may be better to patch during these hours. Occasionally, long periods of intensive patching at school will slow a child's progress.
  7. Treat skin irritation early. Some children will experience skin irritation where the patch is attached to the face. This may be due to a minor allergy to the adhesive. Switching tape/patch brands may help eliminate the problem.
  8. Tincture of Benzoin. This over-the-counter product available from chemists is a type of glue commonly used in hospitals when bandages or tapes need to be applied. Use a cotton swab to apply the liquid around the eye, then wave your hand over the area to help dry it out before applying the patch. The tincture makes it harder (and a bit painful) for the child to remove the patch. To remove the patch, use a wet, warm washcloth to help massage the patch off.
  9. Do not give up too soon. If the patching is proving impossible then it is reasonable to have some time out for a few weeks before trying again. As long as the child is still young there should be time to reverse the amblyopia. There are occasionally times when amblyopia treatment continues to be impossible and you may have to accept that one eye will always be poorer than the other. It is always reassuring to know that you have done everything you can with patching before accepting this.
  10. Tape versus commercial patches. Usually 5cm wide micropore tape is recommended for patching. A 5 x 3cm strip is placed lengthways on the back surface of the longer piece of tape. This provides a smooth surface over the eyelid itself, so that the tape does not stick to the eyelid itself, but allows 1cm at either side to be stuck down around the eye to prevent any peeking. Commercial patches can be obtained from some chemists and from the clinic but are relatively expensive.

Alternatives to facial patches

Spectacle lens patch: If a child wears glasses, then a patch over the spectacle lens is sometimes useful. The patch has to extend back to the forehead from the top of the glasses and along the side of the frame to ensure the child cannot see around it.

Atropine eye drops: These can be used on a daily basis to blur the vision in the good eye. Atropine drops act by relaxing the focusing system of the eye. They also dilate the pupil and can make the eye light sensitive. These drops will work only for certain degrees of amblyopia as they rely on blurring the good eye enough to make it worse than the amblyopic one.

Learn more

Amplyopia section KidsHealth, USA
Find an optometrist NZ Association of Optometrists
Find an eye specialist  Health Pages NZ 

Credits: Used with permission from Auckland Eye. Updated Health Navigator, Jan 2015. Last reviewed: 08 Mar 2015