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Optical Characterization of Bangerter Foils

PURPOSE. Optical penalization is emerging as an alternative topatching for the treatment of amblyopia. Bangerter foils offer aform of optical penalization that is distinctly different fromstandard techniques making use of atropine or spectacle lensmanipulation, or both, to produce defocus. The authors examinedthe optical properties of Bangerter foils and comparedthem with the effect of defocus.

METHODS. Bangerter foils were evaluated on an optical bench tocalculate point spread and modulation transfer functions. Retinalimages through the foils were also simulated and qualitativelycompared with those with defocus and Gaussian blur.Subjective visual acuity and contrast sensitivity were comparedin two subjects wearing spectacles with foils and with simpledefocus.

RESULTS. The optical characteristics of the Bangerter foils donot correspond well with their labeled density designation.Bangerter foils and defocus affect the modulation transfer functionsimilarly, with more attenuation of mid-range spatial frequenciesthan low spatial frequencies. However, Bangerterfoils do not exhibit spurious resolution and phase shifts, asdoes defocus.

CONCLUSIONS. The blur resulting from Bangerter filters is qualitativelydifferent from defocus. Whether this difference is ofany consequence when these two methods of optical penalizationare used for amblyopia treatment remains to beinvestigated.

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