A Randomized Trial of Full-time Bangerter Filters Versus Part-time Daily Patching for the Treatment of Moderate Amblyopia in Children

Amblyopia is the most common cause of monocular visual impairment in children, estimated to affect as many as 3.6% of the childhood population. The natural history of amblyopia is relatively unknown although it has been reported that visual acuity may deteriorate further without treatment.

Although occlusion or patching of the sound eye has been the mainstay for amblyopia therapy, alternative treatment such as pharmacological or optical penalization may be as effective. In a randomized, controlled clinical trial of 419 children, 3 years to less than 7 years old with moderate amblyopia, patching was compared to atropine. Although improvement with atropine was initially slower, both treatments produced similar improvement after 6 months.

Although both patching and atropine have been proven effective for treating amblyopia, neither treatment is without adverse side effects. Patching is associated with compliance difficulties, the need for continuous monitoring, and social stigma. Negative side effects observed in children treated with atropine include light sensitivity, facial flushing, and fever. In a randomized clinical trial comparing patching to atropine as a treatment for amblyopia, a questionnaire to assess the impact of patching and atropine treatment on the child and family indicated that both treatments were well tolerated overall, however, patching had lower compliance and higher social stigma than atropine.

Bangerter filters, also known as Bangerter foils, have been used mainly as secondary amblyopia therapy following patching or atropine to either further improve or maintain the visual gain. One advantage of Bangerter filters compared to patching is that the lower density filters are not readily apparent and therefore would be expected to increase patient compliance due to reduced social stigma. Another advantage of Bangerter filters is that there is no opportunity for skin irritation from bandage adhesive, a commonly-reported side effect of patching. In addition, there is a theoretical advantage that Bangerter filters are less disruptive to binocular function during treatment compared to other modalities such as patching.

Few data are available comparing Bangerter filters with patching for the treatment of amblyopia. Bonsall randomized 14 patients, 3 to 10 years old, with previously untreated strabismic/anisometropic amblyopia to either 6 hours of daily patching or full-time Bangerter filters. Baseline amblyopic eye acuity was 20/30 to 20/400 for the patching group and 20/30 to 20/200 for the Bangerter group. The Bangerter filter prescribed was the minimum density foil needed to elicit a switch in fixation from the sound eye to the amblyopic eye. Visual acuity was measured every 6-8 weeks until the amblyopic eye visual acuity was equal to that of the sound eye, an improvement that was achieved in 5 of the 14 at the time the study was stopped. The average time to achieve equal vision between the amblyopic and sound eyes was about 4.5 months (142 days) for the foil group versus about 9 months (272 days) for the patching group. Both forms of therapy were equally tolerated. Despite good preliminary data, a large randomized clinical trial comparing the effectiveness of Bangerter filters to patching for the treatment of amblyopia has yet to be conducted.