The development of motor fusion in strabismic amblyopes using the Bangerter foil

Abstract

Purpose: To examine the possibility the Bangeter foil encourages the development of motor fusion in strabismic amblyopes without motor fusion. Methods: Fifty-four consecutive amblyopes with small to moderate angle horizontal strabismus (“flick” to 20Δ), spectacles, and no motor fusion for at least 1 year previous were given a (0.1) Bangeter foil 4 hours/day to treat residual amblyopia or for maintenance. Motor fusion was tested by looking for a convergent version of the amblyopic eye in response to a 10Δ base-out prism while binocularly viewing a near target without the foil. Data on visual acuity, angle, and results of the 10Δ test were collected for a minimum of 2 years. Results: Twenty-eight of 46 patients (60%) developed motor fusion (“converters”) after a mean of 201 days. Seven patients were lost to follow-up, and one required surgery. There was no significant difference in the mean initial visual acuity in the amblyopic eye (20/40+, 20/30−) or initial horizontal angle (8.25Δ, 10.12Δ) between converters and nonconverters, respectively. There were significant differences in mean initial age (4.78 years, 5.85 years; p = 0.043) and final angle (6.14Δ, 9.25Δ; p = 0.022). There was also a significant decrease in the mean angle (−2.33Δ; p = 0.007) associated with conversion. Conclusions: Amblyopes with small to moderate horizontal angles, good initial visual acuities, and no motor fusion as measured by a 10Δ base-out test may develop motor fusion when treated with the Bangeter foil. These results are consistent with Parks’ 4 to 8Δ rule and further suggest there may be a mechanism for realignment.