Disturbing optical phenomena

Nick Mamalis MD Dysphotopsias may be the most significant issue that negatively affects patient satisfaction after uncomplicated cataract surgery, said Nick Mamalis MD. Speaking at the 37th Congress of the ESCRS in Paris, France, Dr Mamalis discussed the epidemiology, aetiology and management of dysphotopsias may be the most significant issue that negatively affects patient satisfaction after uncomplicated cataract surgery, Data on how many people experience dysphotopsias after cataract surgery varies, and most surgeons think that the incidence is low because patients may not spontaneously report the problem. However, a study in which complaints were elicited showed that dysphotopsias affect up to 50% of patients early after surgery. “Most of the time the symptoms go away or people get used to them, but dysphotopsias can persist and be a significant issue for some patients,” said Dr Mamalis, Professor of Ophthalmology, John A Moran Eye Center, Salt Lake City, UT, USA Dysphotopsias are broadly categorised as positive and negative. Between the two types, positive dysphotopsias are less common, but they are more visually disturbing than negative dysphotopsias and less likely to resolve spontaneously. Positive dysphotopsias are perceived as bright forms in the visual field, including rings, arcs, halos or flashes of light. “Imagine how disturbing it would be to your visual function if when driving at night, the light from an oncoming car’s headlight is directed right in the centre of your vision,” Dr Mamalis said. The incidence of persistent positive dysphotopsias is reported to be as high as 1.5%, and it varies depending on IOL material and optic design. Reports of the problem began to increase when hydrophobic acrylic IOLs were introduced, and it is also associated with 
a sharp edge optic design. “Frosted or textured edges as well as bevelled designs have been implemented by manufacturers to decrease the intensity of stray light and the incidence of positive dysphotopsias, Dr Mamalis said. He added: “Edge design may explain why silicone IOLs are rarely associated with positive dysphotopsias.” In patients bothered by persistent positive dysphotopsias, IOL explantation and exchange using an implant made of a different material and especially with a round-edge optic can be effective for resolving the problem, Dr Mamalis said. Negative dysphotopsias Negative dysphotopsias are seen as a dark crescent or shadow in the temporal visual field. “Affected patients describe what they feel would be the sensation of horses wearing blinders on their eyes,” Dr Mamalis said. According to the literature, more than 15% of patients report negative dysphotopsias on the day after cataract surgery, but within two months, the symptom resolves in the majority of patients. Negative dysphotopsias are a persistent problem after cataract surgery for between 0.2 and 2.4% of patients. “Negative dysphotopsias do not necessarily go away, but rather there may be cerebral adaptation. However, because they often resolve, surgeons should not rush to intervene when patients complain about negative dysphotopsias early after surgery.” The aetiology of negative dysphotopsias is a subject for ongoing research. Findings from ray tracing analysis suggest the phenomenon may be related to the internal reflection of light around the peripheral edge of the IOL, leading to a dark, non-illuminated area in the peripheral nasal retina. “But it may not be that simple,” Dr Mamalis said. Space between the iris and the IOL surface and the relationship between the anterior edge of the capsulotomy and the anterior IOL surface may be involved. IOL design and material may also be factors considering that negative dysphotopsias are seen more often in patients with an IOL featuring a square edge optic and with hydrophobic acrylic lenses, although they can occur with any IOL material. Options for treating negative dysphotopsias include placing an IOL in the ciliary sulcus or implanting an add-on IOL that will diffuse the light before it reaches the primary IOL. Reverse optic capture of the existing IOL with placement of the optic over the edges of the anterior capsule is also an alternative that targets the relationship of the capsular bag edge and IOL as the potential cause. Laser anterior capsulotomy to increase the size of the anterior capsular opening has also been tried, and novel IOL designs have also been introduced. One, developed by Samuel Masket MD, features a groove on the anterior optic surface that allows a lip of the optic to override the anterior capsule. This approach is supported by evidence that the bag-in-the-lens IOL, which fixates the capsular bag behind the anterior lip of the optic, decreases the incidence of negative dysphotopsias. Another recently proposed modification features an optic with a peripheral concave surface that would redirect light rays to illuminate the dark region of the nasal retina. “Exchanging the IOL in-the-bag for one with a different material and round edge design is often not effective, providing further evidence that the factors causing negative dysphotopsias may not be simple as the lens material or optic design,” Dr Mamalis said. Nick Mamalis: nick.mamalis@hsc.utah.edu

Tags: dysphotopsias