Eyeworld

EW FEATURE 36 by Michelle Dalton EyeWorld Contributing Writer Understanding positive dysphotopsia The visual disturbances exacerbated by ocular surgery can range from annoying to disabling P ositive dysphotopsia—the unwanted images includ- ing rings, arcs, and central flashes that become both- ersome after IOL implan- tation—have been associated with everything from the patient's ability to recognize the edge of the im- planted IOL to corneal disease to multifocal IOLs to an oversized pe- ripheral iridotomy (PI) that allows too much light scatter in the back of the retina. Like most visual anomalies post-surgery, it's nearly impossible to determine who will be affected and who will not beyond a generalized "anyone who is at risk for glare or halo postop." Numbers may not bear it out, as positive dysphotopsia may not result in an IOL exchange but will result in substantial additional chair time after uneventful cataract surgery. In short, these patients are unhappy, and the wrong approach to take is to reinforce the surgery was "perfect." "Square-edge IOLs that reduce posterior capsule opacification (PCO) and have higher index of refractions (acrylic) will have an ini- tial result of about 15% who notice positive and negative dysphotopsia that decreases to less than 5% by one year," said Jack Holladay, MD, professor of ophthalmology, Baylor College of Medicine, Houston. It's not just the IOL, added William Trattler, MD, in practice at the Center for Excellence in Eye Care, Miami. "If someone is on tam- sulosin and the iris is not managed well intraoperatively, you can dam- age the iris," he said. "Iris defects can lead to glare and/or halo that can result in positive dysphotopsia." Simple under- or overcorrection can also lead to the unwanted aberra- tions, although this can be managed with spectacles, he said. Jeremy Kieval, MD, in practice at Lexington Eye, Massachusetts, added the cornea and ocular surface can adversely impact vision postop, and while the IOL's optics and the design of the optic edge have been implicated in numerous studies, he cautions surgeons against excluding other potential causes. "I usually think about the im- plant, but you can't forget about the surface of the eye, the iris, and the capsule," he said. "Multifocal IOLs will cause positive dysphotopsia, due to the edge of the optic as well as the concentric rings." But severe dry eye and other corneal disease "can have some induced aberrations just from the ocular surface that they are perceiving as positive dysphotopsia," he said. Treating the surface issues before surgery will substantially reduce the potential for aberrations postop, he added. "You want to avoid aberrations that are induced by the cornea and not the implant," he said. Irregular topography should be considered before lens selection to minimize the risk as well. Frosting or texturing the edge of the IOL can help reduce—but not eliminate—the occurrence of posi- tive dysphotopsia, Dr. Holladay said. "Marie-Jose Tassignon, MD, developed an IOL with flanges that has totally eliminated the problem, but it is not available in the U.S. and requires a posterior capsulorhexis," Dr. Holladay said. In Europe, the need to create a PI as part of the Visian ICL (STAAR Surgical, Monrovia, Calif.) procedure has been eliminated by the latest iteration of the implant, but again, that version is not available in the U.S. In the U.S., square-edged IOLs were developed to try and prevent PCO, but the square-edge design led to patients having portions of their retina exposed to reflected light from the optic edge in addition to refracted light from the central optic, Dr. Kieval said. "The location of the end of the peripheral functional retina is an important factor in negative dys- photopsia. There is no simple way to measure this preoperatively so pa- tients at risk for this phenomenon cannot currently be identified, ex- cept it is more likely in the second eye if it occurred in the first," Dr. Holladay said. "Rounded-edge IOLs would reduce the incidence, but it is not worth the increased rate of PCO." When to treat? Dr. Kieval believes there are more patients affected by these dyspho- topsias than are reported, mainly because it's not typically asked about during the follow-up visits. Also, patients may not mention the dys- photopsia unless their daily lives are being significantly impacted, "which is thankfully not too frequently," he said. Additional chair time may be necessary to fully grasp the patient's level of discomfort, but in general, if the patient has merely noticed the dysphotopsia but is not complaining about it, "there is no reason for intervention," Dr. Holladay said. "Anterior capsule opacification often ameliorates the symptoms, so inter- vention is rare." Dr. Kieval also prefers to use IOLs with zero asphericity in pa- tients with irregular corneas "be- cause negative aspheric lenses can potentially contribute to positive dysphotopsia if they're not perfectly centered, and can induce other higher order aberrations because the cornea is, essentially, already aber- rated." Dr. Holladay disagrees, saying "there is no evidence that aspheric- ity has any relationship to dyspho- topsias; it is primarily a result of edge design. The improvement of one line of visual acuity, 0.3 log units of contrast sensitivity, and a reduced reaction time with night driving of 0.3 seconds with aspheric IOLs with negative spherical aberra- Pseudophakic dysphotopsia April 2014 AT A GLANCE • Positive dysphotopsia will become problematic for a small portion of patients. • Most issues will resolve over 3 to 6 months. • Ensure the cause of the dysphotopsia is the implant and not poor surface health before considering an IOL exchange. • Piggyback IOLs and Nd:YAG may be viable treatments to consider. Piggybacking an IOL can help to stave off dysphotopsia. Source: Samuel Masket, MD

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