April 2019

IN FOCUS

Innovations in Lenses
Needed IOL innovations


by Rich Daly EyeWorld Contributing Writer


Illustration of the origin of negative dysphotopsia (ND) and one of many positive dysphotopsias (PD). Light entering a pseudophakic eye from the temporal periphery can strike the square edge of an IOL if it is sitting far enough behind the pupil and its optic diameter is sufficiently small. Some light from a polished, square edge design will reflect and strike the temporal retina, producing one of the many PDs. Light that reflects off the edge is not available to traverse the edge,
leading to an arc-shaped shadow over the nasal retina, which causes ND.
Source: Kevin M. Miller, MD

A mid the growing number and variety of IOLs, surgeons see key areas where patient needs remain unmet.
Needed IOL changes that would not necessitate entire redesigns include either moving away from acrylic materials or adding a higher index of refraction acrylic material, said Kevin M. Miller, MD.
But the primary IOL design challenge stems from edge design.
“The thing we know about dysphotopsias is that they suddenly appeared with the introduction of the square edge,” Dr. Miller said.
Initially, dysphotopsias were linked to both square edge and higher index refraction materials. Now square edges are seen as the primary culprit in regard to positive dysphotopsia.
That earlier understanding was challenged by a study1 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 categories of dysphotopsias: negative dysphotopsia (ND), a temporal dark shadow; positive dysphotopsia (PD), peripheral and central light streaks or flashes; and multifocal dysphotopsia, demonstrated 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 PD2,” 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.
“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. Surgeons 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 single-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 haptic 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.

Sulcus lenses

No lens has been brought through an FDA trial for sulcus placement, so no available lenses are specifically designed for placement in that location, Dr. Masket said. A three-piece silicone, 6.3 mm IOL with polyimide haptics that is no longer available was the best off-label option for U.S. surgeons.
Europe has one approved lens specifically designed for sulcus placement (Sulcoflex, Rayner), which is a single-piece hydrophilic available in low powers or as a piggyback lens to add multifocality.
Among materials, Dr. Masket said silicone and hydrophilic acrylic are well tolerated but hydrophobic acrylic tends to be “tacky,” and some patients have developed marked iris chaffing from it.

Single-piece IOL vs. three-piece IOL

Dr. Holladay said there is a need for a single-piece IOL over a three-piece IOL for lower powers (+5 to –10) in high myopia eyes.
“But the frequency is so low, it is not cost effective for most companies,” Dr. Holladay said.
Dr. Masket warned about iris chafing concerns from meniscus design IOLs, which have a thin center and a thick edge. The thick, square, tacky, acrylic material can damage the posterior iris.
In terms of addressing presbyopia in patients who have had previous cataract surgery, Europe has an approved lens (Sulcoflex) specifically designed for that situation, and surgeons have obtained good results with it. U.S. regulatory approval may be complicated by the lack of an existing lens designed for sulcus placement.
“All of that said, there is a new FDA pathway for devices that fit unmet needs; clearly this is such a device, and they might be able to bring it to market with a less onerous pathway,” Dr. Masket said.
Additionally, as a presbyopic device, the lens has the advantage of being clearly reversible should the patient be intolerable of the diffractive add-on optic. “There is potentially a huge market for this device and I would hope that it becomes available to patients in the U.S.,” Dr. Masket said.
 

At a glance

• Research indicates acrylic IOLs are not driving negative dysphotopsias.
• Positive dysphotopsias may be minimized by larger optics, round edges, and low index.
• Needed IOLs include single- piece lenses for those patients below –10 D.
• U.S. surgeons need access to a lens specifically designed for placement in the sulcus.

Contact information
Miller
: kmiller@ucla.edu
Masket: avcmasket@aol.com
Holladay: holladay@docholladay.com

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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