Amblyopia

 

Amblyopia

Definition

Amblyopia is the medical term used when the vision in one of the eyes is reduced because the eye and the brain are not working together properly. The eye itself looks normal, but it is not being used normally because the brain is favoring the other eye. This condition is also sometimes called lazy eye.

Source : National Eye Institute

Amblyopia or "lazy eye" is a condition in which the eye and brain are not working together as they should.

From birth until about 6 years of age, vital connections are formed between a child's eyes and brain. Anything that blocks or blurs vision in one or both eyes may then inhibit or block the development of these connections. This can cause the brain to not fully recognize the images seen by one or both eyes.

When this happens, the brain begins to ignore or suppress the images seen by the otherwise healthy eye, and the eye becomes weaker, losing vision strength (acuity). This eye is then referred to as "amblyopic."

Source : Kids Health

 

Symptoms

It is not easy to recognize amblyopia (lazy eye) in children. A child may not be aware of having one stronger eye and one weaker eye. Unless the child has an eye that is misaligned or another condition that can be seen, there is often no way for parents to tell that something is wrong.

Some symptoms of amblyopia (lazy eye) to look for in a child include:

  • Poor vision in one eye or overall poor vision
  • Squinting, tilting the head or closing one eye to see
  • Poor depth perception (difficulty judging relative distances between objects)
  • An inward- or outward-wandering eye
  • Headaches

Source : AAO 

 

Frequency

It's estimated that about 2 to 3 percent of the U.S. population has some degree of amblyopia.

Source : All About Vision

 

Causes

The following factors can raise a child's risk of having amblyopia (lazy eye):

  • Having misaligned eyes (strabismus)
  • Severe nearsightedness or farsightedness in both eyes
  • Unequal vision in both eyes (one eye more nearsighted or farsighted than the other)
  • Having a condition that prevents light from entering the eye correctly, such as cataract or possibly a droopy eyelid
  • Family history of amblyopia or strabismus
  • Premature birth or low birth weight

Source : AAO

One of the most common causes of amblyopia is strabismus, or wandering of one or both eyes either inward (called esotropia), outward (called exotropia), up (hypertropia), or down (hypotropia).

When eyes are misaligned, the straight or straighter eye may become dominant. The vision strength (acuity) of the straight eye stays normal because the eye and its connection to the brain are working normally. The misaligned or weaker eye, though, does not focus properly and the brain suppresses or ignores its signal, eventually leading to amblyopia.

Not all kids with amblyopia will have crossed or wandering eyes — in fact many have eyes that are perfectly straight. If so, amblyopia is usually the result of an anatomical or structural problem that interferes with or blocks vision, such as a droopy eyelid or a cataract.

Another cause of amblyopia is severe far-sightedness (hyperopia), near-sightedness (myopia), or astigmatism (a form of blurry vision). These vision problems ("refractive errors") cause vision to be blurry, and it's these blurry images that are sent to the brain. Over time, the brain begins to ignore or suppress these unclear images, resulting in amblyopia in one or both eyes.

Another cause could be having different vision strengths in each eye — a condition known as anisometropia. When one eye sees more clearly than the other, the brain can ignore or suppress the vision of the blurry eye.

Genetics play a role, too. Amblyopia tends to run in families. It's also more common in children born prematurely or those affected by developmental delays.

Source : Kids Health

 

Evolution

As a rule, the younger the child is treated, the quicker the improvement in vision is likely to be and the better the chance of restoring full normal vision. If treatment is started before the age of about 6-7 years then it is often possible to restore normal vision. If treatment is started in older children then some improvement in vision may still occur. However, full normal vision is unlikely to be achieved.

About 1 in 4 children develop a recurrence of amblyopia on stopping treatment. This risk is higher if patching is stopped abruptly, and is the reason for careful monitoring. If the problem returns, further treatment is usually needed.

It is very important to follow the advice given to you by an eye specialist (an orthoptist or ophthalmologist) about patching (or other amblyopia treatments) carefully. The most common reason for a treatment failure is because the patch has not been worn correctly for long enough. As your child grows older, the vision pathways will become fully formed and impossible to change, so early patching is essential. 

Source : Patient

 

Prevention

Though modern amblyopia treatments might improve vision in older children and adults, most experts agree that early detection and treatment of lazy eye is preferred for normal visual development and the best visual outcomes from amblyopia treatment.

The American Optometric Association recommends that all children have their first eye exam at 6 months of age, another exam at age 3 and a third exam prior to entering school to ensure vision is developing normally in both eyes and there is no risk of amblyopia.

Source : All About Vision 

 

Diagnosis

Amblyopia can be diagnosed by examining the eyes and testing vision. Different techniques are used to test vision, depending on the age of the child. Children with a known squint (strabismus) are monitored carefully to see if amblyopia develops.

Children in the UK are usually offered a routine preschool or school-entry vision check. One of the main reasons for this is to detect amblyopia whilst it is still treatable. However, even if your child has had an eye check in the past, tell your doctor if you suspect that vision in one or both eyes has become poor.

A baby or child with a suspected amblyopia is usually referred to an orthoptist. Orthoptists are specially trained to assess and manage children with squint and amblyopia. If necessary, an orthoptist will refer a child to an eye surgeon (ophthalmologist) for further assessment and treatment. 

Source : Patient

 

Treatment

Treatment for amblyopia involves forcing the brain to pay attention to the images of the amblyopic or weaker eye so that vision in that eye gets stronger. This is done through glasses, eye patches, eye drops, surgery, or a combination of these:

Glasses. Glasses are prescribed when amblyopia is caused by severe refractive errors and/or anisometropia (when one eye sees more clearly than the other). Glasses help send clear, focused images to the brain, which will teach it to "switch on" the weaker eye. This allows the brain to use the eyes together and develop normal vision.

Eye patches. In many cases, kids with amblyopia must wear an opaque eye patch over their stronger or unaffected eye. The patch is worn for 2-6 hours a day while the child is awake for several months or years, depending on the severity of the condition. There are two types of eye patches: the first type works like a band-aid and is placed directly over the eye. The second type, designed specifically for kids who wear glasses, is a cloth patch that fits securely over one lens.

For parents, enforcing the use of an eye patch might seem challenging. But kids usually adapt well after an initial adjustment period, and the patch simply becomes part of their day. In the meantime, distraction with a new or exciting toy, a trip to the park, or just playing outside can help kids forget they're wearing an eye patch.

Atropine drops. Sometimes, despite parents' best efforts, some kids just refuse to wear their eye patch. In these cases, atropine drops may be used as an alternative to patches. Just as a patch blocks the vision in the unaffected or straight eye, atropine drops will temporarily blur out the vision in the strong eye, forcing the brain to recognize the images seen by the weaker eye.

Surgery. If strabismus is the cause of a child's amblyopia and treatment with glasses, patches, or drops doesn't improve the alignment of the eyes, eye muscle surgery might be an option. Surgery also might be done if amblyopia is caused by a droopy eyelid or a cataract.

Surgery involves loosening or tightening the muscles that are causing the eye to wander. Although it is an invasive measure, surgery is considered safe and effective and usually does not require an overnight hospital stay.

Source : Kids Health

 

Images

  A child wearing an adhesive eyepatch to correct amblyopia

Child eyepatch

SourceBy National Eye Institute, National Institutes of Health [Public domain], via Wikimedia Commons

 

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