Simulation of Retinal Images in Eyes Wearing Bifocal HCL Using a Point Spread Function Analyzer

Abstract

Abstract: : Purpose: To predict the optical function in eyes wearing bifocal rigid gas permeable contact lens (RGPCL) by simulating its retinal image using a point spread function (PSF) analyzer. Methods: Simulation of retinal images was obtained using a PSF analyzer (Topcon, Tokyo). The optical characteristics of the eye were evaluated on the basis of the PSF of a light beam reflected from the retina when a point light is projected on the ocular optic system. A model eye was used for the experiment which had anterior radius of curvature and refraction equivalent to 7.70mm and –5.12D, respectively. The trial lens utilized was monofocal or bifocal concentric RGPCL, the added refraction for near vision in the latter being +0.75, +1.25 or +1.75D. The center of the lens and the visual axis for light projection in the model eye was either concurrent, or the lens was worn 0.5mm to 2mm lower on the model eye. The PSF was measured with an artificial pupil 4mm in diameter. Simulation of the retinal images of Landolt’s rings formed on the retina of the model eye was synthesized from the PSF data. Results: With monofocal RGPCL, little influence on the simulated retinal image due to the shift in lens position was recognized. With bifocal RGPCL adding +0.75D correction for near vision, the image quality did not deteriorate significantly when the lens position was shifted down 1.5mm or less. The image blurred when the shift in lens position was 2mm or more. With those adding +1.25 D or +1.75 D for near vision, the simulated retinal images blurred in the form of the Landolt’s rings dragged toward the superior direction when the lens position was shifted down 0.5mm or 1mm, retinal images becoming remarkably indistinct when the lens was shifted down 1.5mm or more. Conclusions: Predicting the retinal image seen with shifting in multifocal RGPCL position by simulation of the retinal image using a PSF analyzer may provide guidance in prescribing bifocal contact lens.

Keywords: contact lens • visual acuity • optical properties