Results--A Randomized Trial Comparing Part-time Versus Minimal-time Patching for Moderate Amblyopia (Two v. Six)
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 refractive error between the two eyes, such as nearsightedness, farsightedness, or astigmatism. Less common causes of amblyopia are cornea and lens diseases and injury to the eye of a young child. The results reported in this study do not include amblyopia from these less common causes.
Despite the common occurrence of amblyopia, there has been little quality data on its natural history. For decades, patching the unaffected eye had been the standard treatment for amblyopia (In March 2002, researchers reported the effectiveness of drug therapy with a cycloplegic eye drop [atropine] that dilates the pupil and blurs the image seen by the unaffected eye). However, opinions varied widely on the number of hours of patching per day that should be prescribed. No prior study had provided conclusive evidence of the optimal number of prescribed patching hours. This information would be crucial, since reported rates of compliance for patching varied widely, from 49 to 87 percent. Compliance with the prescribed dosage of patching hours is an important factor in determining the level of success of amblyopia treatment.
A Randomized Trial Comparing Part-time to Minimal-time Patching
To address the clinical issue of the optimal number of patching hours for moderate amblyopia, researchers conducted a clinical trial called A Randomized Trial Comparing Part-time to Minimal-time Patching for Moderate Amblyopia. Its purpose was to compare two hours versus six hours of daily patching for children with moderate amblyopia (20/40 to 20/80) and less than seven years of age. The study was funded by the National Eye Institute and conducted by the Pediatric Eye Disease Investigator Group (PEDIG), a network of eye care professionals at universities and community offices in North America. The PEDIG professionals have a goal of determining the best treatment for various eye problems in children.
Between May 2001 and May 2002, 189 patients entered the trial, with 95 randomly assigned to the two-hour patching group and 94 assigned to the six-hour patching group. The number of patients enrolled per site at the 35 sites ranged from one to 21 (median three). The average age of the patients was 5.2 years; 44 percent were female, and 85 percent were white. To avoid including in the study those patients whose prior treatment was unsuccessful, enrollment was restricted to children who had not been previously treated for amblyopia; or had not received patching treatment within six months of enrollment and had not received other amblyopia treatment of any type (other than eyeglasses) within one month of enrollment.
Parents in both groups were advised that the daily hours of patching should be continuous when possible. In addition to patching, parents were instructed to have the child spend at least one of the hours of patching time each day doing "near" visual activities, such as reading, writing homework assignments, making crafts, coloring, tracing, cutting out objects, connecting dots, doing hidden pictures and word finds, playing computerized video games, or other activities requiring eye-hand coordination. Instructions of one hour of near activities were identical in both the two-hour and six-hour patching groups.
After four months, 97 percent of patients in the two-hour group and 95 percent in the six-hour group completed the primary outcome exam. Patients in both groups showed substantial improvement in the eye with amblyopia, averaging 2.40 lines from baseline in each group. At four months, 79 percent of patients in the two-hour group and 76 percent of patients in the six-hour group had improved by two or more lines on the eye chart.
Vision in the unaffected eye decreased by either one or two lines on the standard eye chart in about 21 percent of patients in the two-hour group, and about 24 percent of patients in the six-hour group. However, this is normal for patients with amblyopia, and vision in the unaffected eye is expected to return to normal when treatment is completed.
Researchers note that the amount of vision improvement after four months in the eye with amblyopia should not be considered to be the maximum amount of improvement that can occur with patching. Instead, four months represented the maximum length of time they believed the treatments could be maintained in the study before either increasing the prescribed number of hours of patching or switching to an alternate treatment for amblyopia might be necessary.