An estimated 2 percent to 3 percent of the population has what is commonly known as "lazy eye," a visual disorder in which the brain and one eye do not work together properly. If treated, particularly if treated early, lazy eye - or amblyopia - can, in the majority of cases, be corrected, says Dr. Michael X. Repka, professor of ophthalmology at the Wilmer Eye Institute at Johns Hopkins.
Could you further describe what amblyopia, or lazy eye, is?
What we are thinking of when we say "lazy eye" is decreased vision in one of the eyes that is not correctible with glasses. The decrease in vision is from no apparent cause, meaning the structures of the eye look healthy.
What causes lazy eye?
At birth, a baby's brain, including its visual processes, is not fully developed. Its development depends upon focused images being sent to the brain (by the eye), and if those focused images are never sent, then the brain can't develop. So if your eyes are out of focus, the brain isn't getting good images and isn't developing. If one eye sees clearly and the other doesn't, the brain begins to favor the clearer eye, which makes it grow stronger.
Who is at risk for amblyopia?
Ninety-five percent of cases are caused by either having an uneven refractive error between the two eyes (a refractive error is what you measure "out of focus" to be) or the presence of strabismus, or misalignment of the eye (being cross-eyed or wall-eyed, which is when the eyes turn out). I should add that not every patient who has a strabismus gets lazy eye, or amblyopia.
What are the symptoms?
In children with unequal refractive errors, lazy eye is often asymptomatic. In those with strabismus, you may see crossed eyes, and often this is noticed by the parents or doctor.
How is amblyopia diagnosed?
A good way to diagnose it is screenings held in preschools, schools and pediatricians' offices. Some parents will decide to have their children's eyes examined for this specifically, particularly if they [themselves] had lazy eye.
What is the treatment?
The treatment is to make the person use the [weaker] eye. The first thing we try is correcting the vision of that eye, usually by giving the patient glasses. Then I have the child wear the eyeglasses for a short period of time (perhaps four, eight or 12 weeks). The focused vision allows the brain to develop - basically it is maturing - and correct the vision. It is like a baby learning to walk: Give it the information, and it can learn.
If that doesn't work, then we put a patch over the good eye so you basically force the child to use the other eye. It usually takes about 12 weeks.
Are there other options beyond an eye patch?
An eye drop called atropine can be placed in the good eye a few times a week. It blurs the good eye and makes the child use the lazy eye. This method can be easier for the parents because a drop can be placed in the eye once a day and the parent doesn't have to supervise the use of the patch. It turns out to be a little slower, but not much.
Do you recommend that children be screened for amblyopia?
Absolutely, all children should have an eye screening in the first year of life and at 3 or 4 years of age. I said eye screening - I am not saying they should get a full-court eye exam necessarily. But at least a screening so they can be sure their vision is normal. Some parents might want to go the next step and take their child for an eye exam, but that isn't something that I would suggest for everybody.
Holly Selby is a former reporter for The Baltimore Sun.