Amblyopia is a relatively common eye disorder that presents itself as diminished vision in one (unilateral) or both (bilateral) eyes of an individual. The condition is more common in infants and young children, affecting an estimated 3-5% of the population. It is one of the leading causes of impaired vision in children.
Vision develops early in childhood during the ‘critical period', usually before 8 years of age. Any interferences of the visual pathway at this stage could lead to reduced visual activity among other ocular problems. Amblyopia develops when the brain, by focusing on only one eye, inhibits the cortical activity of the weaker eye in a child. This results in poor visual development either unilaterally or bilaterally.
Also Known As
Amblyopia is classified into three major types based on the underlying cause:
- Strabismic amblyopia
- Refractive amblyopia
- Deprivational amblyopia
Causes and Risk Factors
The most common cause of amblyopia is strabismus, a condition of apparent misalignment of the eyes. In this case, one of the eyes is usually focused ahead while the other is turned either inward, outward, upward or downward. To avoid double vision, the brain responds by suppressing the visual input of the defective eye. This ultimately prevents proper visual development of the child and results in amblyopia.
The other cause of the disorder is unequal refractive errors, otherwise referred to as anisometropia. This is where one eye significantly suffers from a refractive error such as nearsightedness, farsightedness or general blurry vision much more than the other. The brain in this case acknowledges images from the eye with less refractive error and tunes out the vision from the other eye.
Obstruction of light in one eye can also cause amblyopia. This is known as deprivational amblyopia. The common causes of this type of amblyopia are conditions such as ptosis, cataracts, cornea opacities, and vitreous hemorrhage.
A family history of amblyopia or related eye disorders such as strabismus, refractive errors or opacities puts your child at a higher risk of developing amblyopia. Infants born prematurely, with low birth weight or with conditions such as down syndrome are also at a risk.
Signs & Symptoms
In most cases, children appear to be asymptomatic. However, one should watch out for signs such as wandering of the eyes, misalignments, and poor depth perceptions. Other abnormalities such as cataracts, tilting of the head to see better and frequent squinting should prompt an immediate eye check up.
Amblyopia can easily be detected through comprehensive vision examinations. The tests may include visual acuity checks by use of acuity charts, photo screening for ocular defects such as cataracts, and other ophthalmic exams. Once amblyopia is found, treatment should begin immediately.
Treatment is directed towards improving vision in the amblyopic eye by either forcing its usage or correcting the underlying problem in the lazy eye.
Medical treatment of amblyopia involves use of corrective lenses, contact lenses and most commonly, the use of patches. While lenses rectify impairment such as refractive errors in both eyes, patches are placed over the stronger eye in order to improve the visual activity of the defective eye. The patches should, however, be used with caution to prevent deprivational amblyopia on the ‘good’ eye.
An alternative approach in treating amblyopia is penalization. This involves using atropine eye drops or fogging of the stronger eye. The drops work like patches, forcing the brain to acknowledge images from the defective eye. The atropine drops however blur the vision of the ‘good’ eye instead of completely obstructing it. Fogging involves use of excessively strong lenses, as prescribed by the eye doctor or by placing semi-opaque materials over the lens of the stronger eye.
Surgery may involve loosening or tightening of the eye muscles for proper eye alignment, correction of droopy eyelids, or removal of cataracts for a clear visual pathway.
One way to improve the strength of the lazy eye is to engage in vision therapy exercises. Some of the tools that are useful include mazes, puzzles, drawings and reading books. If coupled with correct use of lenses and patches, vision should improve significantly.
If left untreated, the brain continues to ignore the amblyopic eye until it eventually has no use. However, if managed early enough, particularly during the critical period of development, most children can regain normal vision. Amblyopia gets harder to treat as children grow older and therefore recovering the vision might be impossible where too much vision is lost.
Children should be screened frequently in order to detect amblyopia as early as possible. This enables proper treatment and ultimately, improved vision. Follow-up should also be done about one to three months during treatment and regularly after treatment to avoid regression.