Direct observation of negative dysphotopsia in a physical model of the pseudophakic eye

Abstract

Introduction: Negative dysphotopsia (ND) is a phenomenon affecting pseudophakic eyes where a dark crescent or shadow is perceived in the peripheral temporal visual field. Although is it understood that the size and position of the intraocular lens (IOL) creating a space between the IOL's optic and the iris are involved, the exact aetiology and conditions remains unclear. The purpose of this study was to develop a physical model of the pseudophakic eye and to record ND at the retinal plane in a variety of conditions.Methods: The eye model resembles anatomically the human eye with an aspheric cornea made of PMMA (R = 7.73 mm, Q = −0.24) an exchangeable iris and an IOL holder with variable distance (0.5 to 1.5 mm) from the pupil, representing a pseudophakic anterior chamber depth (pACD) ranging from 4.05 to 5.05 mm. The eye model is filled with distilled water. A camera, in a water‐tight housing is used to record images at the retinal plane. Negative dysphotopsia was investigated using both point sources and extended surfaces for two different pACD values (4.05 and 5.05 mm) and two pupil diameters (3 and 6 mm).Results: A characteristic crescent appeared next to the point spread function (PSF) in the periphery, representing light that was propagated beyond the edge of the IOL. This crescent was more prominent in greater pupil diameters and greater pACD values. When testing with an extended field, a relatively dark band appeared at a specific location at approximately 75 degrees of field angle. Various optical strategies to eliminate negative dysphotopsia can be envisaged including inverted meniscus lenses that ‐naturally‐ have a narrower peripheral gap and allow optical propagation until greater field angles as well as formations that block peripheral light.Conclusion: A peripheral crescent, corresponding to light that misses the IOL's optic results to a double‐peaked PSF for field angles as small as 45 degrees in some conditions (large pupil diameter, deep pACD). Yet, a dark band does not appear until much greater angles, where effectively the part of light passing through the IOL is eliminated while the peripheral crescent persists.