Liam Jordan, Associate Editor
PUBLISHED 3 MARCH 2017
New Torics: What You Need to Know
An in-depth look at the Symfony, ReSTOR and enVista toric lenses.
For years, surgeons outside of the United States have had access to more varieties of toric intraocular lenses than their U.S. counterparts. However, thanks to the recent approval of Alcon’s ReSTOR +3 D multifocal toric and Abbott’s Symfony, as well as a new lens in the pipeline, U.S. surgeons’ options are multiplying. More options, however, means more information to sift through as you put these new lenses into practice. In this article, experienced surgeons offer their insights into the new lenses, both approved and on the horizon, focusing on the AMO Symfony, the ReSTOR +3 D multifocal toric and Bausch + Lomb’s enVista toric, which is currently in trials.
AMO’s Symfony Toric
The recently approved Symfony toric sets itself apart from similar lenses by being the only extended depth of focus lens approved in the United States. This hydrophobic, acrylic EDOF lens is able to achieve this extended-depth-of-focus through some unique design elements. The Symfony has a defractive grating on its face, similar to multifocal lenses, but has some significant differences. The ring structures have z-shaped echelette formations that elongate the focus area, rather than splitting and dispersing the light.
Jim Loden, MD, an ophthalmologist based in Nashville, provides some
The Symfony has four toric models to correct up to approximately 3 D of stigmatism at the corneal plane.
insight into the Symfony’s design: “We’re able to achieve an extended depth of focus through the manipulation of chromatic aberration,” he says. The spherical shape of the lens and the hydrophobic acrylic material elongate the depth of field. By addressing the chromatic aberration, you maintain a higher modulation transfer function and decrease the loss of contrast sensitivity you usually find with traditional multifocal lenses.” The design manipulates the chromatic aberration so that instead of dispersing the light, it helps collapse it into a tight region of focus, which improves contrast sensitivity.
The Symfony has four toric models to correct up to approximately 3 D of astigmatism at the corneal plane. Models ZXT150, ZXT225, ZXT300 and ZXT375 correct 1.03 D, 1.54 D, 2.06 D and 2.57 D of astigmatism at the corneal plane, respectively. “For treating more than that, we have the option of doing bioptics,” says Dr. Loden. “I leave the patient with compound myopic astigmatism; I intentionally leave him with nearsightedness in the IOL calculation. Then I can just do LASIK surgery to correct the rest of the astigmatism. Say someone has six diopters of astigmatism preop. You’re going to get three diopters of it with the Symfony toric and correct 2.75 to three through the refractive surgery, depending on the calculation.”
In terms of postop rotation, Dr. Loden claims that it’s minimal. Because the Symfony lens is similar to the TECNIS Toric IOL, the FDA drew from the TECNIS Toric approval data, which reported that of the first eyes done with the toric lens, 97 percent had <10 degrees of rotation from baseline to six months. “I have presented that data, and I’m basically seeing zero rotation,” he says. “I have not come back and repositioned a Symfony toric yet. For those saying the lens is more prone to rotate, I’m not seeing that at all.” The same study reported more than 90 percent of eyes having ≤5 degrees of axis change between consecutive visits three months apart.
Sioux City, Iowa, surgeon Jason Jones, MD, offers these tips for reducing the risk of rotational issues. “The first is to have a very clean surgical experience without any zonular compromise and have the capsulorhexis overlap the optic for 360 degrees,” he says. “Then, ensure you have complete viscoelastic removal from the posterior surface of the IOL. In my experience, I find that if I evacuate the viscoelastic from beneath the optic, it will disappear [from my view]. However, if I then rotate the lens 180 degrees and go behind the optic again, I’ll sometimes find a very small amount of viscoelastic remaining.
“In addition, though you of course leave the eye nicely closed and secure in terms of the wound, you might want the IOP to be a little lower than with a non-toric lens,” Dr. Jones adds. “This is so you don’t hyperinflate the capsular bag and the anterior segment, and instead have it ‘collapse’ around the haptic peripherally, if you will.
“If you want to avoid a rotational issue, I’d look into a capsular tension ring,” he continues. “The first option along these lines would be a regular CTR that most surgeons are familiar with. This will help ensure the capsular bag is symmetrically expanded and that there’s no ovalization of the peripheral capsule. Ovalization can permit the lens to rotate, and this helps prevent that. The other strategy, though I don’t use it routinely, is to use a Henderson CTR. This device has undulations in the ring structure and it, theoretically, provides an interface for the haptics to interact with, peripherally, thus preventing a rotational problem. The last strategy—which most surgeons probably won’t want to employ—is to do some form of optic capture,” he continues. “In some circumstances you can consider a reverse optic capture in which the haptics are in the bag and the optic is prolapsed through the anterior capsulorhexis. I tend to avoid this in the Tecnis single-piece family because the optic has fairly thick peripheral structure and has a squared-off anterior and posterior edge, and I want to avoid any potential iris chafe. Other single-piece acrylic lenses from other manufacturers might be more agreeable to this strategy, however. For the Tecnis monofocal toric lenses, I’ve also employed optic capture through a posterior capsulorhexis, both secondarily in patients who experience rotation and in primary cases in which I want to avoid rotation. Though this ensures no postop rotation, it’s not for the faint of heart, since you must be willing and able to perform a posterior capsulorhexis.”
To aid in the implantation of the new toric Symfony, Abbott offers an online calculator. Visit it at https://www.amoeasy.com.
