Amblyopia
Penn pediatric ophthalmologists at Children’s Hospital of Philadelphia combine the expertise of ophthalmology, neurology and pediatric ophthalmology to treat amblyopia. To refer a child for treatment, call (215) 590-2791 for an appointment in Pediatric Ophthalmology.
What is Amblyopia?
Amblyopia occurs when one or (rarely) both eyes do not develop the normal capacity to see early in childhood. The visual impairment can be mild to modest, ranging from a relatively good 20/30 to legally blind 20/200. Amblyopia is one of the most common causes of irreversible visual impairment, affecting up to 2% of the population.
‘Seeing’ really occurs in the brain. In order to develop vision, each eye must be used; that is, each eye must be allowed to see objects. If an eye is not allowed to see, then the nervous tissue in the brain represented in the visual center does not develop properly. The visual centers develop within the first 5-6 years in life. Therefore, amblyopia starts in early childhood, and conversely, must be treated in early childhood.
Causes of Amblyopia
There are four basic causes of amblyopia:
- Refractive Error: The eye may be very nearsighted or farsighted or have a lot of astigmatism. In these cases of refractive amblyopia, the images are so blurry that the brain never sees a normally focused image coming from the affected eye.
- Eye Disease: Another disease, such as a cataract, obstructs light that normally enters the eye causing obstructive amblyopia.
- Eye Disease: Another disease, such as optic nerve hypoplasia, damages the eye and vision. This damage is then compounded by amblyopia.
- Strabismus: The eyes may be crossed, otherwise known as strabismus. This situation may lead to strabismic amblyopia. The association between strabismus and amblyopia requires further explanation.
Strabismic Amblyopia
Some children develop ‘crossed eyes,’ otherwise known as strabismus. Amblyopia and strabismus are not the same disease but are closely associated to each other. When a child develops strabismus, the brain usually selects only one eye to see with – otherwise the child would experience double vision (diplopia) that would be very incapacitating.
The unused eye is ‘turned off’ by the brain to avoid seeing double. However, if the eye is not used sufficiently, the visual centers in the brain for that particular eye do not develop normally, leading to amblyopia. Note that amblyopia is a permanent condition beyond the age of 5-6, even though the strabismus can be corrected at any time. Also, note that not all children with strabismus develop amblyopia, and conversely, not all children with amblyopia have strabismus.
Treatment for Amblyopia
Amblyopia is very treatable if it is caught early! As stated above, the visual centers develop early in childhood; they are usually developed by 5-6 years old. Therefore, amblyopia must be detected early and treated appropriately. Early treatment provides the best outcome. The treatment for amblyopia depends upon the cause:
- Refractive amblyopia from astigmatism, farsightedness, or nearsightedness can be treated by glasses and patching.
- Obstructive amblyopia (such as from a cataract) can only be treated if the obstruction is first cleared (e.g., cataract removal). Then, any refractive error must be treated and patching performed to force the eye to be used.
- Patching treats strabismic amblyopia. Treating the strabismus is usually less urgent.
- Amblyopia from other diseases, such as optic nerve or retinal dysfunction, usually involves patching.
Important: Note that the GOOD eye is the eye that is patched to treat amblyopia. Patching the deficient (or amblyopic) eye will make the condition worse!
Patching the ‘Good Eye’
Patching involves placing an occlusive patch over the strong eye for a specific length of time. The purpose of the patch is to force the weaker eye to be used. The length and duration of patching should be carefully prescribed and monitored by an ophthalmologist.
Many parents find patching a young child a difficult experience. This is normal. Patching will usually succeed if caregivers are persistent enough. The use of the patch should not be trivialized: it just important to properly place and use the patch as a medicine or other pill.
There are several potential complications with using a patch.
The most common problem is that patching does not improve vision in the amblyopic eye. In this case, the parent and eye doctor need to discuss the length and duration of the patching, and make sure the child is compliant with the treatment; some children will, for example, remove the patch or peak around the patch with their good eye. Occasionally, irritation from the patch may require using a different type of material.
In some cases, patching can cause reversal of the amblyopia; that is, the previously good eye becomes impaired while the treated eye improves. In this case, the problem can be rectified by reversing the patch or by decreasing the duration of patching. Lastly, some children may develop strabismus after patching. In general, however, treating the amblyopia is still the more important consideration. Alternatively, eye drops can be used in some cases of amblyopia instead of a patch to blur the “good” eye.
Early Detection of Amblyopia
Amblyopia must be detected early. No newborn should leave the hospital until the primary physician has performed direct ophthalmoscopy and checked for a good red reflex. Parents should have their children evaluated if they suspect visual impairment, observe crossing of the eyes, notice a white pupil, or have a family history of amblyopia and/or strabismus.
Verbal children should have annual screening vision exams. Screening vision exams may be conducted in a physician’s office or at school. Abnormal vision in either eye warrants further evaluation by an ophthalmologist.
Visual loss from Amblyopia
Visual loss from amblyopia cannot be treated in older children or adults. Individuals with significant visual loss in the affected eye should wear impact resistant glasses at all times, and protective eyeglasses during high-risk activities.
Individuals with good eyesight in one eye are not handicapped. However, they do need to protect their good eye from secondary injury. Some studies have suggested that amblyopic individuals tend to have a higher risk for secondary injury to their good eye.
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