Eyeworld

I INNOVATIONS IN LENSES N FOCUS 112 | EYEWORLD | APRIL 2019 "A larger diameter may allow a wider field of rays refracted by the IOL, but it also reduces to pencil of rays missing the IOL," Dr. Holladay said. "All it does is move the ND more peripherally." Dr. Miller said optic size is a critical approach to minimizing dysphotopsias, which he views as linking lenses sized almost exclusively to fit the capsular bag. "But when the capsular bag is torn, we use those same lenses in the sulcus space where they are not optimal," Dr. Miller said. Available IOLs are either single-piece lenses or three-piece lenses, but there are no single-piece IOLs for patients who are highly myopic. Sur- geons treating patients below 5 D or 6 D must move to a three-piece design, which lacks larger diameters. Another issue Dr. Miller raised about three- piece lenses is that they are more likely to be destroyed or kinked by injector systems. He urged IOL manufacturers to add sin- gle-piece lenses with options available for those patients below –10 D. It's more likely that PD can be addressed by larger optics, round edges, and low index. The only large foldable lens on the market—a 6.5 mm lens (MA50, Alcon)—has a square edge and has not reduced the incidence of PD or ND among Dr. Masket's patients. Although surface reflectivity, as determined by index of refraction, is a factor in PD, Dr. Masket said, the optic size does not seem to play a role in ND. He cited the example of the Crystalens (Bausch + Lomb), which has the smallest optic—5 mm—and a relatively low incidence of ND. "This is primarily because the surgical capsulotomy is larger than the optic, as one of the chief issues of ND is the overlapping capsule," Dr. Masket said. Dr. Holladay agreed myopia patients need larger optic, lower index of refraction, larger hap- tic lenses available in lower powers. "But in general, it is a larger anterior segment that requires larger haptics," Dr. Holladay said. Among materials that would best serve unmet needs, both in terms of haptics and the optic, Dr. Holladay said lower index of refraction acrylic seems to be the best for the optic. That earlier understanding was challenged by a study 1 in the Journal of Cataract & Refractive Surgery. The study, which looked at the largest series of patients undergoing surgical correction for chronic negative dysphotopsia and included 40 eyes, found 23% were silicone lenses and 13% had round edges. "There's a misconception that acrylic IOLs are causal of negative dysphotopsia; there's no clinical evidence to support that," said Samuel Masket, MD, who was the lead author of the study. However, moving back to rounded edges could return the challenge of posterior capsule opacification (PCO), which square edges retard. "If we went back to a rounder edge the problem would go away, but no one wants to do that because you trade that problem for another problem," Dr. Miller said. The sheer magnitude of dysphotopsia as a chief source of patient dissatisfaction has been met with limited help from IOL manufacturers, Dr. Masket said. Dr. Masket said lenses need to address all cat- egories of dysphotopsias: negative dysphotopsia (ND), a temporal dark shadow; positive dyspho- topsia (PD), peripheral and central light streaks or flashes; and multifocal dysphotopsia, demonstrat- ed by halos or spiderwebs. Dr. Masket has designed a lens that aims to eliminate ND; it is in European clinical trials. Jack Holladay, MD, has also reviewed several new proprietary designs that address ND and PD, and include changed parameters around the shape of IOL, edge design, material, and asphericity. "Each of the factors directly contribute to both ND and PD 2 ," Dr. Holladay said. Some designers have frosted the edge, which can scatter the light hitting the square edge to minimize visual impacts. A square anterior edge may be unnecessary in the sulcus, where it can scrape against the iris, while a square posterior edge can be retained and frosted, Dr. Miller said. Optic size Views were mixed on the impact of optic size on reducing glare related to ND or PD. Dr. Holladay viewed the IOL diameter as having little effect on ND. continued from page 110 About the doctors Jack Holladay, MD Clinical professor Baylor College of Medicine Houston Samuel Masket, MD Clinical professor of ophthalmology David Geffen School of Medicine University of California, Los Angeles Kevin M. Miller, MD Kolokotrones Chair in Ophthalmology David Geffen School of Medicine University of California, Los Angeles References 1. Masket S, et al. Surgical management of negative dysphotopsia. J Cataract Refract Surg. 2018;44:6–16. 2. Holladay JT, Simpson MJ. Negative dysphotopsia: Causes and rationale for prevention and treatment. J Cataract Refract Surg. 2017; 43:263–275. Financial interests Holladay: AcuFocus, Alcon, ArcScan, Carl Zeiss Meditec, Johnson & Johnson Vision, M&S Technologies, Oculus, RxSight, Visiometrics Masket: Morcher Miller: Alcon, Johnson & Johnson Vision, Carl Zeiss Meditec

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