In the search for the best presbyopia treatment, a lot of attention has been paid to multifocal and diffractive intraocular lenses, while there's been little movement on the accommodating IOL front. That may change in the next year, as the clinical investigators and company researchers at Visiogen are readying their Phase III data for the Synchrony dual-optic accommodating IOL for submission to the Food and Drug Administration. Here's a look at this technology, its long-term international results and the injector that makes the whole package work.
One Lens, Two Optics
The Synchrony is the first dual-optic accommodating IOL, and is a single-piece silicone lens that has a high-powered +32 D anterior optic joined to a rear minus-powered optic by flexible silicone spring-like struts. The medical monitor for the
"Ophthalmologists and patients want improved accommodating lenses that can reduce spectacle dependence without the inherent drawbacks of multifocality. Many surgeons and patients currently forego choosing a multifocal IOL because of unwanted images at night, the slight reduction in contrast sensitivity, and a limited range of intermediate vision," Dr. Chang explains. "The hope with an accommodating lens is to be able to accomplish the upside of some reading ability without any optical drawbacks in comparison to a monofocal lens." Dr. Chang says that for any moving optic, the resulting amount of accommodative shift is proportional to the dioptric power of the IOL. This limits the accommodative potential for myopic patients requiring lower-power optics. "The concept behind a dual-optic accommodating system is to be able to place a very high-powered moving optic in every eye and then use a rear minus optic to adjust the net power to whatever is needed for the individual eye," he says. "What varies is how much minus is in the rear optic, while the anterior optic is greater than 30 D in every eye."
The Lens in Action
Dr. Chang says the struts connecting the two silicone optics were carefully designed to produce a precise amount of spring-like tension.
"The Synchrony operates according to the Helmholtz mechanism of accommodation," he explains, "with tensing and relaxation of the zonules in response to ciliary muscle contraction and relaxation. As the capsular bag relaxes, the front optic is allowed to move forward, which increases the effective lens power. Conversely, as the bag tenses, the two optics are compressed together, restoring distance focus. You can view the forward movement of the anterior optic with high-frequency ultrasound biomicroscopy."
The challenge with the Synchrony involved getting the large lens into the eye, however. "When we started our studies of the lens," recalls Colombian surgeon and Visiogen consultant Ricardo Alarcon-Jimenez, "we used forceps to implant it, which was really difficult because it's two lenses in one."
Early on during the evolution of lens, the company knew it needed a reliable injector, says Dr. Chang. "A pre-loaded injector system was eventually developed, and it has made implantation of this complicated lens design surprisingly manageable. What the injector does is to first displace the rear optic ahead of the front optic by way of a sliding tray," Dr. Chang explains. "Both optics are then compressed into the lumen of the injector. The surgeon uses a plunger to advance the lens into the eye, one optic at a time. The injector requires a larger incision than for current monofocal IOLs, and I prefer about a 3.7- to 3.8-mm incision, as measured with an incision gauge."
Dr. Chang says that the capsulorhexis must be round, well-centered and slightly smaller than the anterior 5.5-mm diameter optic.
"The capsulorhexis must be small enough to completely overlap and restrain the forward-moving anterior optic," Dr. Chang explains. "If the capsulorhexis is too large, or it's eccentric so that it fails to overlap one part of the anterior optic edge, you can't insert the lens.
"The surgeon also has to get visually oriented as to what part of which optic is emerging out of the injector first," Dr. Chang continues. "Typically, you have to make minor manipulations to properly position the two optics. At that point, the lens will completely fill the capsular bag—and you can't really see the rear optic, which is obscured by the front optic—and the surgeon uses bimanual irrigation/aspiration to completely remove the OVD, which includes any amount sandwiched between the two optics."
The results from the Synchrony's FDA trial of nearly 450 implantations at 20 investigator sites are currently being tabulated and aren't available for publication. Dr. Alarcon-Jimenez, however, implanted 84 lenses in 42 patients, and has two years of follow-up in 22 implantations.
"At 24 months, over 95 percent of the cases had 20/40 or better distance vision," Dr. Alarcon-Jimenez says. "All had better than 20/34 intermediate visual acuity and 95 percent had 20/40 or better near visual acuity." At two years, 85 percent can use the computer or read a newspaper without spectacles.