Can the Riddle of the Negative Dysphotopsia Be Solved?

William W. Culbertson, MD


September 28, 2012


A small fraction of patients perceive a dark crescent-shaped area in the temporal visual field following routine, otherwise successful cataract surgery. They come to the office with drawings that precisely outline what they see and a list of the conditions in which they are most likely to see it. These patients are often fearful that "something is wrong" such as a retinal detachment or movement of the IOL. In the title of their report, the study authors coined the term for this annoying negative dysphotopsia an "enigmatic penumbra" because of the misunderstood nature of the cause of this inconsistent phenomenon. Equally enigmatic to surgeons has been how to explain to patients why they have the bad luck to experience this personally, while their next-door neighbor who had "the same surgery by a different surgeon" is not experiencing it. At least now the patient's surgeon can offer up the explanation that his or her eye was different, anatomically, from the neighbor's eye, and this difference creates the "dark arc" that they sometimes see.

Surgeons and patients have been frustrated by the lack of dependable remedies for this problem when the time-honored conservative recommendation that "it will go away in time" doesn't turn out to be true. Thus, this "enigmatic penumbra" has been an enigma of cause and prevention, as well as of treatment -- Churchill's proverbial "...riddle, wrapped in a mystery, inside an enigma ......"[4]

Indeed, negative dysphotopsia can resolve spontaneously. "Transient" dysphotopsia (2 weeks in duration) can be explained by the hydration of a temporally placed clear corneal incision that gradually resolves in a few weeks as the incision area dehydrates. "Temporary," more slowly resolving dysphotopsia caused by the projection of the optical void (penumbra) of a square-edged IOL on the nasal retina could gradually be lessened in time as the peripheral capsule opacifies and diffuses/scatters obliquely entering light rays, illuminating the previous penumbra zone in the nasal retina with unfocused light. So-called "neuroadaptation" could also account for temporary cases that resolve in 6-12 months.

It is the persistent, lingering cases that annoy patients and perplex surgeons. For these situations, IOL manipulation, IOL exchange, and piggy-back IOL implantation may be helpful but not necessarily curative.

According to the theoretical model presented in this study, rotating the IOL haptics to a horizontal nasal-temporal orientation could serve to diffuse the obliquely entering light rays in the case of a 3-piece haptic that inserts into the optic with a short circumferential component. In 1-piece IOLs, in which the area of the haptic junction with the IOL serves to expand the IOL in that area, the effectively widened area of the optic would theoretically cause the retinal intercepts of the shadows to be more anterior and smaller in width and thus be less perceptible.

Exchanging a square-edged IOL with a frosted-edged IOL, a rounded-edged IOL, or a silicone IOL with a lower refractive index and a rounded edge all are treatments that may reduce but not eradicate the patient's annoying perception.

Finally, secondarily implanting a rounded-edged piggyback IOL anterior to the existing IOL would be predicted by the model to reduce the space behind the iris, and the rounded edge would diffuse light striking the peripheral retina. However, the addition of a piggyback IOL could possibly change the refractive error, resulting in further discontent in an already unhappy patient.

These palliative strategies could be applied in a preventive way to minimize the possibility of negative dysphotopsia occurring in the fellow eye, such as using a rounded-edged 3-piece silicone IOL oriented with the haptics horizontally instead of a square-edged acrylic IOL oriented vertically.

In summary, this interesting and thoughtful paper eloquently serves to elucidate the "enigma" of the crescent-shaped penumbra, validates some of the anecdotal reports in the literature, and offers reasonable, but not perfect, remedies for this perplexing and recurring problem. An IOL design that both eliminates this optical phenomenon and at the same time prevents posterior capsule opacification would be embraced by all surgeons.