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 nerve cells responsible for vision do not mature normally.
In the United States, amblyopia affects approximately 2 percent of all children. It is the most common cause of partial or total blindness in one eye in the U.S.
The term "lazy eye" is misleading because the eye is not lazy. In fact, it is a developmental problem in the nerve connecting the eye to the brain, not a problem in the eye itself.
- Symptoms of lazy eye include blurred vision and poor depth perception.
- Lazy eye is not a problem with the eye, but the connections to the brain.
- Amblyopia can be caused by a number of factors, including a muscle imbalance or eye disease.
- Treatment can be effective and the sooner it begins, the better.
Amblyopia is a relatively common problem.
Treatment tends to be more effective the younger the child is.
After a child is 8 years old, the likelihood of vision improvement drops significantly but can still be effective.
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, or anisometropia, do not know they have an eye problem because the stronger eye and the brain compensate for the shortfall. The weaker eye gets progressively worse, and amblyopia develops.
Glasses: A child with near-sightedness, far-sightedness, or astigmatism will be prescribed glasses. The child will have to wear them all the time so that the specialist can monitor how effective they are at improving the vision problems in the lazy eye. Glasses may also correct an eye turn. 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.
Cataract surgery, or phacoemulsification: If a cataract is the cause of amblyopia, it can be surgically removed under either local or general anesthesia.
Correcting droopy eyelids: For some people, amblyopia is caused by an eyelid that is blocking the vision to the weaker eye. In this case, the usual treatment is surgery to lift the eyelid.
Getting the lazy eye to work
Once the vision is corrected and any underlying medical issues are addressed, then there are several other actions that can be taken to help improve vision.
Occlusion, or 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 information from that eye, it will not ignore it. A patch won't get rid of an eye turn, 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.
Atropine eye drops: These may be used to blur vision in 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 with a patch, and can be just as effective. Children who cannot tolerate wearing a patch may be prescribed eye drops instead.
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.
Surgery: Sometimes, eye surgery is performed to improve the appearance of an eye turn, resulting in better alignment of the eyes. This may or may not improve vision.
Exercises to help correct vision known as orthoptics. However, there are initially no specific exercises that can help to improve amblyopia.
The stronger eye may be patched, and the weaker eye stimulated with a range of vision-intensive activities, such as coloring, dot-to-dot drawing, word games, or building Lego, depending on the age of the child.
Other exercises, such as home-based pencil push-ups (HBPP), may be used once strength has returned to the weaker eye. These involve slowly moving a pencil towards the tip of the nose and focusing on the end of the pencil during this movement until it becomes blurry.
However, home-based exercises are not likely to be used for people with amblyopia as a first-line treatment. Many orthoptic exercises require vision in both eyes and are intended for people with different vision problems.
Anything that obstructs vision in either eye during a child's development has the potential to cause lazy eye. Although the reasons are not clear, the brain suppresses the images coming from the most affected eye.
Below are examples of some possible causes.
This is an imbalance in the muscles that position the eye that causes the eyes to cross or turn out. The muscle imbalance makes it difficult for both eyes to track objects together. Strabismus may be inherited, or be the result of far- or near-sightedness, a viral illness, or an injury.
A refractive error is when the light is not focused correctly as it travels through the lens of the eye. Refractive errors occur due to nearsightedness, farsightedness, or astigmatism, in which the surface of the cornea or lens is uneven, causing blurred vision.
A child with anisometropic amblyopia will be more far-sighted or near-sighted in one eye than the other, resulting in amblyopia developing in the eye that is most effected.
Stimulus deprivation amblyopia
This is the least common form of amblyopia. One eye is prevented from seeing and becomes weaker. Sometimes, both could be affected.
This could be due to:
- a corneal ulcer, a scar, or another eye disease.
- a congenital cataract, in which a baby is born with clouding of the lens
- ptosis, or a droopy eye lid
- eye injury
- eye surgery
Symptoms of lazy eye include blurred or double vision.
A child with amblyopia 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 will not receive clear images. The brain will not receive clear data, and will eventually start to ignore it.
In many cases, the brain and the stronger eye make up for the shortfall so well that the child does not notice they have a problem. That is why lazy eye is often not detected until the child has a routine eye test.
Symptoms of a lazy eye may include:
- blurred vision
- double vision
- poor depth perception
- eyes do not appear to work together
- an eye turn, either upward, downward, outward, or inward
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.
Early diagnosis is essential, preferably before the age of 6. Because the child often does not realize there is a problem, this is not always possible.
Routine eye examination
Amblyopia is often picked up by a routine eye test.
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.
If the ophthalmologist or optometrist 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 near- or far-sightedness, and how serious it is. The child will also be carefully tested to determine whether there is an eye turn.
Blindness: If untreated, the patient may eventually lose 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 U.S.
Eye turn: Strabismus, where the eyes are not properly aligned, can become permanent.
Central vision: If amblyopia is not treated during childhood, the patient's central vision may not develop correctly. The problem may affect their ability to do certain tasks.