Quantification And Analysis Of Negative Dysphotopsia And Associated Phenomena In A Physical Model Of The Eye

Negative dysphotopsia (ND) is a photic phenomenon affecting pseudophakic eyes where a dark crescent or shadow is perceived in the peripheral temporal visual field. Although is it understood that the edge of the intraocular lens (IOL) and the space between the IOL’s optic and the posterior iris are involved, the exact etiology remains unclear especially with respect to its clinical manifestation. The purpose of the study was to develop a physical model of the pseudophakic eye and to record ND at the retinal plane in a variety of conditions.

Diestia Systems PC, Athens Greece

The eye model resembles anatomically the human eye with an aspheric cornea made of PMMA (R=7.73mm) an exchangeable iris and an IOL holder with variable distance (0.5 to 1.5mm) from the pupil, representing a pseudophakic anterior chamber depth (pACD) ranging from 4.05 to 5.05 mm. The eye is filled with distilled water. A camera, in a water-tight container is used to record the retinal images. 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). 

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 70 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.

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.