Negative dysphotopsia: the enigmatic penumbra.

PURPOSE: To determine the cause of negative dysphotopsia and the location, appearance, and relative intensity of such images in pseudophakic eyes.

SETTING: Baylor College of Medicine, Houston, Texas, USA.

DESIGN: Reporting available data addressing a specific clinical question.

METHODS: Negative dysphotopsia was simulated using the Zemax optical design program. The nominal values for the pseudophakic eye model were as follows: IOL power, 20.0 diopters (D); corneal power, 43.5 D; Q value, -0.26; axial IOL depth behind pupil, 0.5 mm; external anterior chamber depth (corneal vertex to iris plane), 4.0 mm; optic diameter, 6.0 mm; pupil diameter, 2.5 mm.

RESULTS: From the first ray-tracing simulation, analysis of the image for the nominal parameters showed 2 annuli (ring-shaped) shadows. The inner annulus shadow was located from a retinal visual field angle of 86.0 to 100.0 degrees (width 14.0 degrees), and the outer annular shadow was located from 105.9 to 123.3 degrees (width 17.4 degrees). Superimposing the inner annulus on the human visual field showed that the shadow would be apparent only temporally, where it is within the limits of the visual field and functional retina. The patient would perceive this as a temporal dark crescent-shaped partial shadow (penumbra).

CONCLUSIONS: Primary optical factors required for negative dysphotopsia are a small pupil, a distance behind the pupil of 0.06 mm or more and 1.23 mm or less for acrylic, a sharp-edged design, and functional nasal retina that extends anterior to the shadow. Secondary factors include a high index of refraction optic material, angle α, and the nasal location of the pupil relative to the eye's optical axis.

FINANCIAL DISCLOSURE: Drs. Zhao and Reisin are employees of and Dr. Holladay is a consultant to Abbott Medical Optics, Inc. No author has a financial or proprietary interest in any material or method mentioned.