Lens Adjustment After Cataract Surgery in View

Laird Harrison

October 14, 2019

SAN FRANCISCO — Specialists currently struggling to improve their calculation of intraocular lens power for patients undergoing cataract surgery should look to the cornea, but in the future, postoperatively adjustable lenses could be the way to go, experts said here at the American Academy of Ophthalmology 2019 Annual Meeting.

Currently, only 70% to 80% of cataract surgeries are accurate within ±0.5 D of predicted values, said Douglas Koch, MD, from the Baylor College of Medicine in Houston. And rates for complex eyes are even worse.

But "the one thing we can do most about in our practice is the cornea," he said.

In 2008, one researcher estimated that effective lens position accounted for 35% of errors, axial length accounted for 27%, and refraction accounted for 17% (J Cataract Refract Surg. 2008;34:368-376).

But that has changed, Koch said, because optical biometers — such as optical or swept-source biometry — are so much more accurate than those used in the past that axial length is no longer a significant source of error.

Effective lens position and refraction remain important factors, but the anterior and posterior surfaces of the cornea also enter into the mix, he added.

To begin to address problems of intraocular lens calculation, he explained, formulas should be categorized by mechanism: geometric optics, which differ by the number of variables they use to calculate effective lens position; ray tracing; artificial intelligence; and combination formulas.

"The common goal of all these formulas, one way or the other, is to calculate or to compensate the effective lens position," said Koch.

In principle, ray tracing should work best because it incorporates all the positions of either the cornea or the implanted lens, but that has not been the case. Because each region of the eye has a unique index of refraction, the segmentation of axial lengths can improve accuracy in both long and short eyes, he explained.

We may nail it on the operating table but then it may change as the patient heals.

Preoperative and postoperative optical coherence tomography has shown that effective lens position shifts unpredictably, with one study documenting an anterior chamber depth shift of more than 1 mm from 1 hour to 2 months in 17.6% of eyes (J Cataract Refract Surg. 2018;44:642-653).

"We may nail it on the operating table but then it may change as the patient heals," Koch said.

Short eyes (<22 mm) are especially challenging, he pointed out, because a small shift gives you a lot of refractive change.

Post-LASIK eyes are also "bumping against" a 70% success rate, said Koch, and keratoconus poses an even bigger challenge. The steeper the cornea, the greater the hyperopic error.

"We do need more than one measurement, and we need to verify the quality of our raw data before we use them for our calculations," he said. Multizone light-emitting diodes can be used to measure corneal curvature, he recommended.

With a variety of new lens types in development, postoperative adjustment will likely become mainstream, said Koch. "These are exciting technologies to improve our outcomes."

Postoperative Adjustment

There are three categories of intraocular lens that can be adjusted postoperatively, Burkhard Dick, MD, PhD, from the University Eye Hospital in Bochum, Germany, explained at the meeting.

Two categories require secondary procedures for power adjustment: multicomponent, mechanically adjustable, and repeatedly adjustable lenses; and magnetically adjustable and liquid-crystal lenses with wireless control. In contrast, femtosecond laser, two-photon chemistry, and light-adjustable lenses can be adjusted noninvasively.

"The multicomponent technology is more or less for specific indications," said Dick. Laser-induced refractive index change (LIRIC) research is under development and "there are clinical trials underway," he reported. The two-photon approach has worked in rabbit trials, he added.

In addition, "upgraded light-adjustable lens technology just started commercially in Europe with great success. I think it offers great options to improve refractive incomes," he said.

The new version of the light-adjustable lens (LAL 2.0) is a 13.0 mm, foldable, three-piece silicone lens with enhanced ultraviolet light absorption implanted with a proprietary injector though an incision less than 2.75 mm wide.

The LAL 2.0 can be adjusted to an extended depth of focus, or to correct up to 2 D of myopia or hyperopia, said Dick. It can be used to achieve individually adjusted mini-monovision and to induce negative asphericity.

In a prospective trial, Dick and his colleagues implanted the lens in 100 eyes of 50 patients with 0.5 D to 3.0 D of preoperative keratometric astigmatism. They found that more patients had 20/20 uncorrected distance visual acuity after the lenses were adjusted than before (73% vs 33%).

Koch reported financial relationships with Alcon, CAPSULaser, Carl Zeiss Meditec, Ivantis, Johnson & Johnson Vision, PerfectLens, and Vivior. Dick reports financial relationships with Allergan, Avedro, Bausch + Lomb, Carl Zeiss Meditec, Johnson & Johnson Vision, Johnson & Johnson, Oculus Surgical, Oculus, Optical Express AG, Polytech-Domilens, and RxSight.

American Academy of Ophthalmology (AAO) 2019 Annual Meeting. Presented October 11, 2019.

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