The term “amblyopia” derives from the Greek word for “dullness of vision.” It is estimated that amblyopia affects two or three of every 100 children in the United States. The disorder is caused by conditions that affect normal visual development. These conditions can include an imbalance in the positioning of the eyes, such as strabismus, in which the eyes are crossed inward (esotropia) or turned outward (exotropia). Amblyopia can also result from a major difference in the refraction between the two eyes, such as nearsightedness, farsightedness, or astigmatism.
Despite the common occurrence of amblyopia, there has been little quality data on its natural history or on the outcomes of two forms of treatment of this disorder –occlusion therapy (patching) and topical drug therapy. Patching the unaffected eye has been the standard treatment for amblyopia, despite the lack of meaningful data demonstrating its superiority over other treatments. Reported rates of compliance for patching widely range from 49 to 87 percent. There is evidence that compliance is an important factor in determining the level of success of amblyopia treatment.
An alternative treatment –drug therapy with a cycloplegic eye drop (atropine) that dilates the pupil and blurs the image seen by the unaffected eye –has been known for almost a century. This method has been widely used when occlusion treatment does not work. However, it has seen little use as a primary treatment for amblyopia.
Prior to this study, a few small studies had suggested that atropine eye drops might be useful for treating mild to moderate degrees of amblyopia. If this were true, atropine drug therapy might be preferred as an initial treatment for many children with amblyopia, since it appears to be more readily accepted by the children and their parents. However, the use of atropine as a primary therapy for amblyopia had gained only limited use among pediatric ophthalmologists. A 1997 survey by the Pediatric Eye Disease Investigator Group (PEDIG) found that only three percent of eye care professionals prescribed atropine eye drops as a primary treatment of amblyopia, while 97 percent preferred patching. A definitive study to compare the outcomes from occlusion therapy and drug therapy was justified to determine if new practice guidelines for treatment of amblyopia were needed.
The Amblyopia Treatment Study was conducted to determine whether atropine was as effective as patching for treating amblyopia in children less than seven years of age. The study was funded by the National Eye Institute and conducted by the PEDIG, a network of eye care professionals at universities in North America and in local community offices. The PEDIG professionals have a goal of determining the best treatment for various eye problems in children.
Between April 1999 and April 2001, 419 patients entered the trial. The average age of the children at the beginning of the study was 5.2 years; 47 percent were female; and 83 percent were white. Enrollment was restricted to children who had either not been previously treated for amblyopia or who had received no more than two months of treatment in the prior two years. Each patient was randomly assigned to either the patching or atropine groups. Ninety-seven percent of those assigned to the patching group and 95 percent of the assigned to the atropine group completed the study.
The minimal patching time was six hours per day; some children were patched during all waking hours. This time was reduced or increased, depending on the success of the treatment at 16 weeks. Researchers judged the compliance rate in the patching group to be excellent in 49 percent of the patients, good in 34 percent, fair in 13 percent, and poor in five percent.
Atropine eye drops were prescribed, one drop a day initially but the frequency could be reduced depending on the success of the treatment at 16 weeks. Sunglasses were provided to the children for use in sunlight due to light sensitivity from the dilated pupils. Researchers judged the compliance rate in the atropine group to be excellent in 78 percent of the patients, good in 18 percent, fair in three percent, and poor in one percent. On a questionnaire completed by the child’s parent or guardian, the acceptability of the atropine treatment was judged to be better than that of the patching treatment.
Side effects were minimal for either group. In the patching group, mild skin irritation was reported at least once in 41 percent of patients, with moderate or severe skin irritation at least once in six percent of patients. In the atropine group, light sensitivity was reported for 18 percent of patients, eye lid or corneal irritation for four percent, and eye pain or headache for two percent. In the atropine group, some of the normal eyes that received the atropine had a temporary decrease in visual acuity. The results are inconclusive about whether this was an effect of the atropine or was due to a need to change the eyeglass prescription.
Atropine therapy is likely to be less expensive than patching. Atropine treatment is estimated to cost about $10 over six months, where an eye patch would cost nearly $100. About 25 percent of atropine-treated patients may need to wear a special lens in their eyeglasses to compensate for the effect of the atropine, at a cost of about $50.
Data from the study will provide valuable information about the course of amblyopia treatment and help determine whether factors such as age and refractive error should be considered in determining which procedure is best for a given patient.