Dr. Jeff Hersh: Symptoms and cures of lazy eye (amblyopia)
Q: The doctor said my grandson has lazy eye and is at risk to lose his vision. He does not look cross-eyed to me -- isn’t that what lazy eye is?
A: Normal visual development occurs from birth through age 5, with the nerve pathway from the eye to the brain developing from birth through age 8.
Amblyopia (colloquially called lazy eye) is a significant decrease (or even loss) of vision due to a problem with development of this nerve pathway. If the brain gets a very strong/interpretable signal from one eye and a minimal/difficult to interpret signal from the other eye, it starts to "ignore" the weak eye, and so the nerve pathway from the weak eye can degrade.
Strabismus, which occurs in 2 to 4 percent of children, is a condition where the eyes are not aligned with each other (so they do not "look" at the same thing at the same time, giving a cross-eyed appearance); it can cause the brain to "ignore" the signal from the misaligned eye, and this is the most common cause of amblyopia. Strabismus can occur from anything that compromises or causes an imbalance in the muscles that are responsible for moving the eyes.
Blurry vision from cataracts, astigmatism, near- or far-sightedness or from anything else can also cause the nerve signal from the affected eye to be "minimal" as compared to the other eye, hence causing amblyopia.
Symptoms of amblyopia, which typically presents in children ages 3 to 5, may include strabismus (so as noted above this can be a cause of amblyopia but it can also be a symptom, as the compromised vision may cause the brain to start to "ignore" the signals from the affected eye), poor depth perception and a rapid decrease in visual acuity. In fact it is the loss of visual acuity of at least two lines on the eye chart that is a factor for the diagnosis of amblyopia.
After the loss of visual acuity is identified, a thorough eye examination is needed to look for anatomic causes. When none are identified and other possible causes are ruled out by an eye specialist, the diagnosis of amblyopia can be made.
Amblyopia, the most common preventable cause of childhood blindness, occurs in anywhere from 1 to 4 percent of healthy kids, and in a higher percentage of children with certain concomitant medical problems (such as those that cause cataracts or other risks for amblyopia).
Since amblyopia is due to inadequate stimulation of the nerve pathway, treatment of it is based on "exercising" the nerve pathway.
The first step is to correct conditions causing blurry vision if they exist, which may be enough to allow the nerve pathway issue to resolve.
For cases where there is no blurry vision, or where correction of the blurry vision is not sufficient, the next step is to place a patch over the normal (stronger) eye to exercise the nerve pathway of the weak eye. The total duration of patching (some literature notes 200 total hours is often sufficient), as well as the amount of time the good eye should be patched each day, depends on many factors, including the severity of the visual loss and response to treatment (as demonstrated by regaining the lost visual acuity).
Some studies have shown that longer patching duration per day may increase the risk of recurrence after patching is discontinued. In some kids, where compliance with patching is not optimal, eye drops to intentionally distort the vision in the good eye can be used.
Surgery to treat some cases of strabismus (if this is a cause of amblyopia) may be considered for cases that do not improve sufficiently with patching.
Patching before age 5 will lead to recovery of visual acuity in about three fourths of kids (although some loss of depth perception may persist), typically within weeks to months. However, up to a quarter of these kids will have their amblyopia recur within the first year after treatment. Most of these recurrences will again improve with patching, although more prolonged patching may be required.
Although it was once felt that patching was not beneficial after age 10 (and the earlier amblyopia is treated the better the results), more recent studies have shown that patching can still be beneficial for some patients even through their teens.
Since early treatment is best, regular acuity screening is indicated for all children. Parents who notice their child is cross-eyed should discuss this with their child’s pediatrician so appropriate evaluation can be done.
Jeff Hersh, Ph.D., M.D., can be reached at DrHersh@juno.com.