What Is Amblyopia?
Amblyopia (lazy eye) is reduced vision as a result of abnormal visual development. Typically, amblyopia occurs in only one eye but can affect both eyes. Lazy eye generally starts between birth and early childhood, which is the critical period for normal vision to develop. During this time, neural connections form between the visual cortex of your brain and your eyes.
Typically, your brain processes visual information from both eyes equally. If one eye cannot see as well as the other eye, the weaker eye does not receive normal visual signals. As a result, your brain starts to favor the stronger eye and suppresses vision in the weaker eye.
If left untreated, a lazy eye can cause permanent vision loss ranging from mild to severe.
Who Is At Risk?
Children are at the highest risk for amblyopia between birth and eight years of age. The chances of an adult developing amblyopia are minimal. Other risk factors include:
- Premature birth
- Low birth weight
- Developmental disabilities
- Down syndrome
- Family history of amblyopia
Symptoms of amblyopia can be hard to detect. In many cases, children do not complain about visual problems or show any signs. They may go undiagnosed until a parent brings them for an eye exam.
Here are some common symptoms of lazy eye:
- Eye that turns in, out, up, or down
- Both eyes do not appear to point in the same direction
- Squinting or closing one eye
- Bumping into objects on one side
- Poor depth perception
- Head tilt
- Flash photography shows different colored pupil reflections (for example, one eye has a bright red reflex while the other has a dim reflex)
If a flash photo reveals a white reflex, this can be a sign of retinoblastoma, a rare but serious eye cancer in children.
Amblyopia affects 2 percent to 4 percent of children under age 15.
Causes of Amblyopia
Several eye conditions can lead to amblyopia. Some of these causes include:
When one eye is misaligned, both eyes cannot focus in the same direction. To avoid double vision, your brain tries to tune out what the misaligned eye is seeing. Some children have intermittent strabismus, which means the eye turn is not present all the time. Because their brain receives visual signals from time to time, they are less likely to develop amblyopia compared to children who have constant strabismus.
Many babies may appear to have strabismus, but in actuality, they have pseudostrabismus. Babies often have broad epicanthal folds, which are the eyelid folds that run from the upper lid to the nose. These folds give the appearance that the child’s eyes turn inwards, when, in fact, the eyes are aligned properly. This condition is temporary and goes away as the baby’s face develops.
Different forms of refractive error include myopia (nearsightedness), hyperopia (farsightedness), and astigmatism. The higher your refractive error, the blurrier you see. Having a significant refractive error in one eye causes the brain to suppress vision in that eye. Children may not complain of vision problems since the better-seeing eye compensates.
Less commonly, amblyopia can occur if both eyes have a high refractive error. However, the amblyopia is mild compared to having a high refractive error in only one eye. Additionally, a high refractive error can cause an eye turn, so it is possible to have both refractive and strabismic amblyopia.
Deprivation amblyopia occurs when something obstructs the line of vision. This type of lazy eye is rare. Conditions that can cause deprivation amblyopia include congenital cataracts, severe droopy eyelids (ptosis), or corneal scars. This type of amblyopia tends to cause more severe vision loss if left untreated.
Amblyopia Treatment Options
Children who receive amblyopia treatment at a younger age have a better visual outcome, so early detection is critical. Amblyopia is more challenging to treat in older children and adults because their visual systems have already developed. Different therapies include:
Many cases of refractive amblyopia can be treated with glasses and contact lenses. If strabismus related to high refractive error is present, correcting the refractive error with glasses often helps straighten the eye out. Glasses with special prism lenses also help to align the eyes.
This treatment involves covering the stronger eye to train the brain to use the weaker eye. Usually, the child must wear an eye patch for at least a few hours a day and during certain activities such as reading. Eye patching is often prescribed if the amblyopia is more severe, and glasses alone may not be adequate treatment.
If eye patching is not effective, or the child resists using a patch, some eye doctors prescribe atropine eye drops to dilate the pupil of the stronger eye. The drops cause blurry vision in the better eye, forcing the brain to rely on the amblyopic eye to see.
Vision therapy helps improve both refractive and strabismic amblyopia. The eye doctor prescribes a program of eye exercises to help improve eye alignment, strengthen eye coordination, develop depth perception, reduce suppression of the lazy eye, and other visual benefits. There are a variety of devices, including computer programs, that are designed for vision therapy.
Some instances of strabismus may require eye muscle surgery to straighten out the misaligned eye, especially if other treatments have failed. This is dependent on the severity of strabismus, the child’s age, and other factors. Some people need more than one strabismus surgery to correct the problem.
If deprivation amblyopia is detected, it is best to treat the problem as quickly as possible since there is a higher risk of irreversible vision loss. Treatment involves fixing the underlying cause, such as cataract surgery or eyelid surgery.