What Is Amblyopia?

This article is amblyopia, colloquially known as ‘lazy eye’. We’ll take you through what a lazy eye is, what causes amblyopia, how to fix a lazy eye with an eye patch, eye exercises and amblyopia surgery.

What Is Amblyopia?

Amblyopia is a vision development disorder in which an eye fails to achieve normal visual acuity, even with prescription glasses or contact lenses. It's estimated that about 2-3% of the US population has some degree of amblyopia.

Amblyopia typically begins during infancy and early childhood. In most cases, only one eye is affected. However, it’s also known to occur in both eyes.

If amblyopia is detected and treated early in life, reduced vision can be avoided, but an untreated case can cause permanent vision loss in the affected eye. 

Amblyopia Signs and Symptoms

Because amblyopia is typically a problem in infants’ vision development, symptoms of lazy eye sometimes can be hard to spot.

A common cause of amblyopia is misalignment of the eyes - a condition called strabismus. 

If you notice your baby or young child has crossed eyes or some other eye misalignment, schedule an appointment with an eye doctor near you immediately - preferably with an optometrist or ophthalmologist who specializes in children’s vision.

You can try a simple amblyopia screening test at home by covering and uncovering your child's eyes (one at a time) when they are performing a visual task like watching television.

If your child is not bothered when one eye is covered, but objects when the other eye is, this may suggest that the eye you have covered is the ‘good’ eye, and that the uncovered eye is amblyopic, causing blurred vision.

Obviously, a simple screening test is no substitute for a comprehensive eye exam.

It's recommended to schedule your child's first eye exam at around 6 months of age to make sure their vision is developing normally and their eyes are working properly together.

How to Tell if Your Child Has a Lazy Eye

A lazy eye does not usually cause symptoms. Younger children are often unaware that there's anything wrong with their vision and, if they are, they're usually unable to explain what's wrong.

Older children may complain that they cannot see as well through one eye and have problems with reading, writing and drawing.

In some cases, you may notice that one eye looks different from the other. However, this is usually a sign of another condition that could lead to a lazy eye, such as:

• A squint – where the weaker eye looks inwards, outwards, upwards or downwards, while the other eye looks forwards 
• short-sightedness (myopia), long-sightedness (hyperopia) and astigmatism
• Childhood cataracts – cloudy patches that develop in the lens, which sits behind the iris (the coloured part of the eye) and pupil

If your child is too young to tell you how good their vision is, you can check their eyes by covering each eye with your hand, one at a time. They might object to covering the good eye, but they might not mind if you cover the lazy eye.

If they try to push your hand away from one eye but not the other, it may be a sign they can see better out of one eye.

What Causes a Lazy Eye?

There are three types of lazy eye, based on these underlying causes:

• Strabismic amblyopia. Strabismus is the most common cause of lazy eye. To avoid double vision caused by poorly-aligned eyes, the brain will ignore the visual input from the misaligned eye, leading to amblyopia in that ‘lazy’ eye. This type of amblyopia is called strabismic amblyopia.
• Refractive amblyopia. Sometimes, a lazy eye is caused by unequal refractive errors in the two eyes, despite perfect eye alignment. For example, one eye may have significant nearsightedness or farsightedness, while the other eye does not. Or, one eye may have significant astigmatism while the other does not. In such cases, the brain relies on the eye that has less severe refractive error and ‘ignores’ the blurred vision from the other eye. This causes amblyopia in the affected eye simply via neglect. This type of lazy eye is called refractive amblyopia or anisometropic amblyopia.
• Deprivation amblyopia. This is lazy eye caused by something that obstructs light from entering and being focused in a baby's eye, such as a congenital cataract. Prompt treatment of congenital cataracts is necessary to allow normal visual development to occur and prevent visual disabilities.

Lazy Eye Treatments

In some cases of refractive amblyopia, normal vision can be restored by fully correcting the refractive errors in both eyes with glasses or contact lenses. Usually, however, at least some patching of the ‘good’ eye is required to force the brain to pay attention to the visual input from the ‘lazy’ eye.

Treatment of strabismic amblyopia (lazy eye caused by misaligned eyes) often involves strabismus surgery to align the eyes, followed by use of an eye patch on the dominant eye and some form of visual therapy to help both eyes work together equally as a team.

It may be necessary to wear an eye patch for several hours each day (or even all day long) for several days or weeks to force the brain to start using the lazy eye normally.

Children may be uncomfortable wearing an eye patch and are prone to taking them off - you may want to consider a specially designed prosthetic contact lens that prevents light from entering the good eye but does not affect your child's appearance.

Though prosthetic contact lenses are more costly than an eye patch and require a contact lens exam and fitting, they can work wonders in difficult cases of amblyopia treatment when compliance with eye patching is poor.

Amblyopia Surgery

In many cases of strabismic amblyopia, surgery must be performed to properly align the eyes before eye patching.

It must be noted that ‘lazy eye surgery’ is a misleading and incorrect term. The correct term to describe surgically straightening the eyes is strabismus surgery.

Sometimes, more than one strabismus surgery is needed to attain adequate eye alignment. Additionally, special eyeglasses with prism lenses might still be required after strabismus surgery to let the eyes work together as a team and for lazy eye treatment to be effective.

Remember: Early detection of amblyopia is essential for the best treatment outcomes. It’s always a good idea to schedule routine eye exams with an eye doctor for you and your children.

If you’ve found this guide to ‘what is amblyopia’ interesting or informative, you can browse the rest of our eye health articles here. Alternatively, you can visit our store here, where we stock a range of prescription glasses and contact lenses.