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, and it has been evaluated systematically in a series of scientific papers. A pdf is included below, along with an initial video simulation of what might make a peripheral dark shadow "bothersome".

This work led to finding that "Far peripheral vision"  appears to be a visual region where there has been very little research (above 60 degrees). A review summarizes the information that is readily available: Simpson MJ. Mini-review: Far Peripheral Vision. Vision Research 140C (2017) pp. 96-105 (a version can be downloaded from the Downloads page).  One question is how the limit of vision varies with age and refractive error, with a limiting visual angle measurement of about 105 degrees dating from 1915, but modern test equipment only extending to 90 degrees at most. What if there happens to be an unexpected connection to myopia development, for example, but there are no data so nobody has noticed... 

"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. This is discussed in the 2021 JCRS paper.