Purpose: Multifocal lenses have been shown to produce enhanced near and intermediate vision. The division of incoming light into more than one focal point must physically produce retinal images of reduced contrast. The purpose of this report is to provide quantitative data on the increased depth of focus and decreased contrast sensitivity demonstrated in patients receiving the 3M diffractive multifocal lens versus the parent monofocal control lens.
Methods: Uncorrected and best-corrected distance and near acuities, Regan and Pelli-Robson contrast sensitivity measurements, and defocus curves were obtained on 22 eyes with monofocal and 16 eyes with multifocal age-matched, pathology-free implants at 1 year after surgery.
Findings: Visual acuity data demonstrated significantly improved (P < 0.001) near acuities in multifocal patients with manifest refraction in place. No difference was noted between implants for other acuity measures. A statistically significant reduction (P < 0.05) in contrast sensitivity was measured for multifocal implants at the limits of contrast and resolution (Regan 4%); however, careful patient questioning revealed no clinical impact. Defocus curves demonstrated significantly increased (P < 0.0001) depth of focus at the 20/40 acuity level of 3.8 diopters (D) in multifocal patients versus 1.8 D in monofocal patients.
Conclusion: The quantifiable and expected loss of contrast sensitivity in the examining lane, not manifest in patient awareness, appears to be an acceptable tradeoff for enhanced near/intermediate vision and depth of focus.