IOL maintains mechanism of accommodation in studies

January 1, 2010

Accumulating results from studies investigating a light-adjustable IOL indicate this technology can afford precise postoperative control over refractive outcomes

"The IOL is a silicone, bag-filling implant that provides the optical quality of vision associated with a monofocal IOL," said Dr. Chang, clinical professor of ophthalmology, University of California, San Francisco. "In studies with follow-up ranging from 2 to 5 years, the posterior capsule in [eyes with implants] is remaining surprisingly clear and there is evidence that the accommodative mechanism of action of this implant and its ability to provide a full range of focus are being maintained over time."

Theory of accommodation

As predicated on the Helmholtz theory of accommodation, ciliary muscle contraction decreases zonular tension resulting in capsular bag relaxation, whereby the compressed optics are allowed to move further apart, producing the accommodative shift, Dr. Chang said.

Inserted using a preloaded injector, the IOL can be delivered through a 3.8-mm clear corneal incision that will be about 4 mm in size following implantation.

Patients should have a well-centered capsulorhexis that is smaller than and completely overlaps the 5.5 mm anterior optic diameter, so that the latter cannot prolapse out of the bag, he said.

"We believe that polishing of the undersurface of the anterior capsule also is important in order to reduce the risk of anterior capsular fibrosis," Dr. Chang said.

Multiple studies

Enrollment of 485 eyes at 20 investigational centers participating in the FDA phase III trial was completed 2 years ago, and the pre-market approval application for the study was submitted in August 2009. Although data from this study are not publicly available, the IOL received the European CE mark in 2006; more than 1,200 eyes have received the implant globally; and there have been several clinical studies from international investigators reporting outcomes after longer-term follow-up.

In Colombia, Ivan Ossma, MD, and colleagues conducted a randomized, patient/examiner-masked study enrolling 100 patients who underwent bilateral implantation of either the dual-optic accommodating IOL or an apodized diffractive multifocal IOL (AcrySof ReSTOR +4 D, Alcon Laboratories)

At 1 year postimplantation, the two IOL groups had similar binocular near visual acuity outcomes as measured through the best distance correction.

Distance-corrected intermediate vision measured at multiple different distances, however, was significantly better in patients with the dual-optic accommodating IOL implanted compared with recipients of the apodized diffractive multifocal IOL.

The dual-optic accommodating IOL group also had significantly better contrast sensitivity than the multifocal IOL group in all testing conditions (mesopic and photopic, with and without glare)

In addition, no patients with dual-optic accommodating IOLs experienced severe halos or glare whereas rates of these complaints in the group with multifocal IOLs were 31.4% and 20%, respectively.

At the 2009 meeting of the American Society of Cataract and Refractive Surgery, Ricardo Alarcon, MD, and Victor Bohórquez, MD, reported findings from their studies of the dual-optic accommodating IOL. They showed that binocular distance-corrected near visual acuity was maintained at 24 months when 95% of 21 patients could read 20/40 or better with distance correction. In addition, the patients experienced no loss in reading speed comparing results from testing at 1 and 2 years.

"This provides important evidence that the near vision benefit of this lens is not lost over time because of capsular fibrosis during the first 2 years," Dr. Chang said.

Studies using high-definition ultrasound biomicroscopy and wavefront aberrometry have provided objective evidence that the anterior lens is moving with accommodative effort, and defocus curves (a subjective measure of accommodation) correlate well with the objective studies.

Dr. Ossma also has 5-year follow-up from a cohort of 17 eyes in patients who received an earlier model of the dual-accommodating IOL. Visual acuity results showed little change in intermediate and near distance-corrected vision, and at 5 years, only 1 eye (5.8%) had undergone Nd:YAG laser capsulotomy. Worldwide, there have been no reports of interlenticular opacity (ILO) in eyes with a dual-accommodating IOL implanted, according to Dr. Chang.

These clinical findings are consistent with the results of a rabbit eye study conducted by Liliana Werner, MD, PhD, examining capsular fibrosis and ILO in the dual-accommodating IOL, and they also compare favorably with data from Dr. Alarcon and Dr. Bohórquez, who reported a 2% YAG capsulotomy rate at 3 years based on follow-up in a larger series of eyes, Dr. Chang said.

Capsular bag clarity

"The clarity of the capsular bag has impressed every investigator who has experience with silicone implants," he said. "Of course, this is the first time we have implanted an IOL that is able to keep the capsular bag completely open and expanded and we believe that this is a key reason for the lack of significant capsular fibrosis in most eyes."

If a YAG posterior capsulotomy is performed, Dr. Chang said, it does not seem to affect the accommodative mechanism of the implant.