Characterization of bangerter filter effect in mild and moderate amblyopia associated with strabismus.

Background: To evaluate the outcome achieved by using Bangerter filters in cases of mild to moderate amblyopia associated to strabismus.

Methods: Prospective study comprising 30 children (age range 2-9 years) with unilateral mild to moderate amblyopia associated to esotropia and hyperopia. All patients were treated by prescribing the use of a Bangerter filter in the non-amblyopic eye in combination with the refractive correction. In all cases, the filter selected induced a reduction of the visual acuity of 2 lines below the best spectacle-corrected visual acuity (BSCVA) of the amblyopic eye. A follow-up of 12 months was completed.

Results: A statistically significant improvement in BSCVA was observed at 3 months in amblyopic eyes (p 0.01), with additional significant improvements at 6, 9 and 12 months (p 0.02). The BSCVA in non-amblyopic eyes remained unchanged during the initial 6 months of treatment (p 0.52), with a significant improvement at 9 months (p=0.03). Significant differences between amblyopic and fellow eyes were only detected at 3 months (p 0.01). Filter density had to be changed during the follow-up in 12 eyes (40%). Inverse significant correlations between baseline filter density and BSCVA were found at the end of the follow-up (r -0.35, p 0.01). A significant correlation of the visual acuity with the baseline visual acuity difference among eyes was only present at 3 months (r=-0.55, p 0.01).

Conclusions: Bangerter filters seem to be useful for treating mild or moderate amblyopia due to strabismus, but ocular dominance inversion should be maintained during treatment for obtaining an optimized outcome.