Expanding binocular depth of focus by combining monovision with diffractive bifocal intraocular lenses

PURPOSE: To test the hypothesis that binocular depth of field can be expanded while retaining high quality vision at intermediate distances by combining anisometropia (monovision) and simultaneous vision bifocals. SETTING: School of Optometry, Indiana University, Bloomington, Indiana, USA. DESIGN: Prospective research study. METHODS: A computational polychromatic model was used to simulate retinal images as seen through a pseudophakic eye with a diffractive bifocal for a range of target distances. Computationally blurred stimuli were presented dichoptically, simulating a binocular pseudophakic person with 1 emmetropic eye and 1 eye with myopia of 0.40 diopter (D), 0.80 D, or 1.20 D. Binocular visual acuity was measured for computationally blurred high-contrast Sloan letters. RESULTS: Ten subjects participated in this study. The emmetropic eye achieved best vision at infinity and near distance specified by the addition (add) power, while the myopic eye peak acuities were achieved at shorter viewing distances. Having 1 myopic bifocal eye had no effect on distance acuities. With a bifocal add of 2.20 D and 1.20 D of anisometropia, the binocular depth of focus was more than 3.00 D and provided binocular acuities of better than 20/20 throughout this range. For each target distance, the binocular acuities closely approached those of the better-focused eye. CONCLUSIONS: By careful selection of unilateral myopia and bilateral use of high-quality bifocal lenses, high intermediate distance acuities can exist with a large depth of field. This approach can improve intermediate vision and expand depth of field without compromising best achievable distance and near acuities.