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Effect of pupil diameter on both negative dysphotopsia and peripheral vision with IOLs

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Session Details

Session Title: Pseudophakic IOL Power Calculation: Photic Phenomena after IOL Implantation

Session Date/Time: Sunday 08/10/2017 | 16:30-18:00

Paper Time: 17:36

Venue: Room 3.4

First Author: : M.Simpson USA

Co Author(s): :    M. Muzyka-Wozniak                    

Abstract Details

Purpose:

Negative dysphotopsia with intraocular lenses (IOLs), where some patients see peripheral dark shadows, has brought attention to light rays that miss the IOL. The primary cause of shadows is probably vignetting, which causes the main focused image to go dim at large angles. Light missing the IOL also illuminates the peripheral retina, however, and this typically reduces or eliminates shadow visibility. With larger pupils, however, the peripheral image extends to lower visual angles. The extent of this secondary image is evaluated.

Setting:

Simpson Optics, R&D Consultancy

Methods:

Unlike the phakic eye, a single retinal location can be illuminated by light from two different input angles, which can create a type of double image. The light missing the IOL “appears” to come from a larger visual angle because it has not been focused by the IOL, and the Zemax raytrace software was used to calculate where rays that just miss the IOL hit the retina, for a range of pupil diameters. The actual ray input angles were then compared to the corresponding “apparent” visual angles, which were calculated in reference to light actually imaged by the IOL.

Results:

As the pupil diameter increased from 2-4 mm, the apparent visual angle of the rays just missing the IOL decreased from 92 to 72 degrees, but then decreased more rapidly down to 24 degrees for a 5.5 mm pupil. The actual input visual angle was only about 4 degrees lower than the “apparent” angle for these rays. For small pupils the illumination is very peripheral, which can leave a dark gap beyond the main focused image, but this “shadow” is rapidly eliminated as the pupil opens. For large pupils, the second image can be present for relatively modest visual angles.

Conclusions:

Negative dysphotopsia is only reported for small pupils, which is consistent with the effect being eliminated by light bypassing the IOL as the pupil opens up. However, for larger pupils the peripheral light becomes superimposed on the main focused image at much smaller angles, and although double images are not usually reported in the periphery, this may be something to bear in mind when evaluating visual phenomena with IOLs. The apparent visual angle at which the second image starts is only a few degrees larger than the actual visual angle, which may reduce its visibility.

Financial Disclosure:

NONE

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