New IOL shows marked improvement in rotational stability and asphericity

Study shows toric IOL reduces residual refractive error and increases MTF function.

The first generation of plate haptic toric IOLs were shown to have rotational instability, causing some surgeons to question the technology. Rotational stability is essential to predictable refractive outcomes giving patients good uncorrected distance or near visual acuity.

Lisa B. Arbisser

With the introduction of the one-piece acrylic toric implant, excellent stability was achieved. Now the new AcrySof Toric IOL (Alcon Laboratories, Inc.) adds the advantages of reducing spherical aberration, enhancing contrast sensitivity as well as dependable stability and giving patients excellent visual results, according to Edward Holland, MD, and Lisa B. Arbisser, MD, who presented their findings on the AcrySof Toric IOL during the American Society of Cataract and Refractive Surgery 2009 meeting.

“This lens is known for its stability due to the lens property and the tackiness, and its ability to stick to the capsule,” Dr. Holland said, adding that when the lens is placed in the right position and allowed to completely open, and when the viscoelastic is eliminated from behind the lens, then the lens stays “absolutely” where it is placed. “And this stability is why this is a better lens,” he said.

Clinical trial results

Dr. Holland, professor of ophthalmology at the University of Cincinnati and director of cornea services at the Cincinnati Eye Institute, supported his claims with results from a prospective clinical trial that studied 517 patients who received either an AcrySof Toric IOL or a monofocal control IOL (first eyes). At study conclusion, bilateral IOLs could be implanted in the patients. The protocol required surgeons to make an incision on the 180-degree axis and to complete surgery without moving the incision. Many times, though, surgeons can change the incision to on-axis to improve visual outcomes, according to Dr. Holland.

The AcrySof Toric IOL was shown to have a mean rotation of 4 degrees or less, and in 98% of patients the IOL rotated less than 15 degrees, according to Dr. Holland. In addition, 78% of the implanted IOLs rotated 5 degrees or less 1 year after surgery.

“We looked at long-term stability of the lens 1 year out and that showed the lens stayed where we put it at the time of surgery,” he said.

The study showed that patients were two times more likely to have less than 0.5 D of cylinder with the toric IOL than with the control IOL. Refractive error less than 0.5 D correlates with excellent uncorrected visual acuity, Dr. Holland said. Mean residual refractive error was found to be 0.59 D in patients who received the toric IOL and 1.22 D in patients who received the control IOL.

Enhanced contrast sensitivity

Dr. Arbisser, who teaches cataract and anterior segment surgery worldwide from her practice, Eye Surgeons Associates in Iowa and Illinois, and is an adjunct clinical associate professor at Moran Eye Center in Utah, stressed the importance of asphericity to the performance of a toric IOL. She explained that an average cornea has positive sphericity and as people age, lens fibers accumulate inside the eye, creating more positive and less negative sphericity. If a spherical lens is implanted in a patient with positive sphericity higher order aberrations are increased, according to Dr. Arbisser.

“When we add negative sphericity to our positive sphericity, we cause all the rays, both marginal and paraxial, to come to a nice sharp point, improving our contrast sensitivity,” improving the modulation transfer function (MTF), Dr. Arbisser said.

AcrySof Toric IOL accurately focuses waves of light into the visual system to improve the MTF, resulting in a sharper, clearer image especially when the pupil is large, as in night-driving.

“We now don’t have to sacrifice asphericity for toricity when we choose the only lens available with both attributes, the AcrySof Toric,” Dr. Arbisser said.