Amblyopia is a developmental cause of vision loss. It occurs during early childhood and can be prevented or limited with early diagnosis and treatment.
Amblyopia is one of the most common eye disorders in children. The condition is often referred to as “lazy eye” and it is present in approximately 3% of the U.S. population. The disorder affects the way the brain processes input from the affected eye.
Any condition that interferes with one eye’s focusing during early childhood can cause amblyopia.
When one eye is not focusing clearly during early childhood because one eye turns inward or there is a refractive error in one eye or a cataract, the unequal input from each eye causes the brain to ignore the information from the weaker eye.
Because all this is occurring during the development of the brain’s visual cortex, if the condition is not corrected it will lead to permanent vision loss in the weaker eye. And that vision loss is not because the eye is damaged but because the brain cannot process incoming visual signals from that eye.
The poorer-seeing eye can be open and healthy and sending visual information to the brain, but the brain ignores the input. If the weaker or misaligned eye is not corrected during early childhood, visual input from that weak or misaligned eye will continue to be ignored by the brain.
Unless amblyopia is successfully treated in early childhood, it will persist into adulthood and cause permanent one-eye vision impairment.
The three most common causes of amblyopia are strabismus, refractive error, and cataract.
Strabismus is a misalignment of the eyes causing one eye to deviate inward toward the nose or outward while the other eye remains focused forward. The forward focusing eye is the only eye that the brain will process incoming visual signals from.
The eyes might be correctly aligned but there is a refractive error in one eye, for example, one eye could have substantial nearsightedness, farsightedness, or astigmatism while the other eye does not. When this happens, the brain becomes reliant on the better eye and ignores the vision from the weaker-seeing eye.
The other cause could be a congenital cataract in one eye or any other disorder that obstructs vision in one eye such as a droopy eyelid.
Treatment for Amblyopia
The best visual outcomes are achieved when the condition is diagnosed and treated in early childhood. The standard treatment method for amblyopia is an eye patch placed on the stronger eye in order to restore the brain’s attention to the visual input from the weaker eye. And if the cause was a refractive error in one eye, then that refractive error is corrected with glasses before the eye patching part of the treatment is started.
If the cause is strabismus—a misalignment of the eyes, then surgery is often used to align the eyes and then continued treatment using an eye patch to retrain the brain to use the incoming visual signals from the formerly misaligned eye.
If the cause was a drooping eyelid or a congenital cataract then surgery is also used first to fix the droopy eyelid or remove the cataract and then eye patching is used.
The outcome of treatment depends on the type of amblyopia and the compliance with the treatment, in other words, if the eye is patched to enable the brain to learn to process the visual signal from the unpatched eye and the child does not consistently wear the eye patch, then that would detrimentally affect the long-term outcome.
But if treatment is started early and is applied consistently, the condition can be completely resolved in the majority of patients.