Negative Dysphotopsia

"Negative dysphotopsia" is the term used to describe the "dark shadows"  that a few intraocular lens (IOL) patients see in their far peripheral vision. The primary cause is highly likely to be the limited size of the IOL in comparison to the natural crystalline lens that it replaces. At very large visual angles the light is no longer imaged by the IOL, and a shadowlike phenomena may be visible. This is actually an imaging property related to IOLs, rather than the casting of a shadow. 

This phenomenon is being evaluated systematically in a series of scientific papers, with the papers themselves containing references to earlier work. This work indicates that "negative dysphotopsia" is actually an expected characteristic of the use of an intraocular lens (IOL), and it has also led to additional questions about far peripheral vision. A summary of the current situation is given below. 

Initial video simulations of what might make a peripheral dark shadow "bothersome" have also been added below. The eye seems particularly sensitive to sudden movement in the far periphery, though it is not clear if this has ever been characterized. One video illustrates the peripheral image jumping across the shadow and changing size. The other illustrates a sudden change in the shadow if the pupil diameter changes. 

"Positive dysphotopsia" is also a potential concern with IOLs, and these are bothersome if there is total internal reflection at the lens edge at night. Discussed in 2021 JCRS paper.