Aspheric multifocal IOL boosts intermediate vision, minimizes aberrations

A study suggests that fewer concentric steps in the +3 D version of the lens result in less higher-order aberration.

Niels E. de Vries

Bilateral implantation of a +3 D aspheric diffractive multifocal IOL improved intermediate vision without diminishing distance or near vision, a study showed.

The +3 D lens resulted in markedly lower levels of higher-order and spherical aberrations and a higher preferred working distance at near compared with a +4 D iteration of the lens, the study authors said.

“Except for patients with a strong preference for a short working distance, the +3 D model is currently our multifocal IOL of choice,” Niels E. de Vries, MD, the lead author, told Ocular Surgery News.

Dr. de Vries and colleagues compared the AcrySof ReSTOR SN6AD1 IOL with a near addition of 3 D and the AcrySof ReSTOR SN6AD3 IOL with a near addition of 4 D (both Alcon).

The +3 D AcrySof ReSTOR IOL was designed to improve intermediate vision without diminishing near or distance visual acuity, the authors said.

Although a recent study compared visual acuity and patient satisfaction with the AcrySof ReSTOR lenses, Dr. de Vries noted that he and colleagues were unaware of research comparing contrast sensitivity, straylight and wavefront aberration measurements.

The study was published in the Journal of Cataract and Refractive Surgery.

Protocol and procedure

The prospective, nonrandomized study included 68 eyes implanted with the +3 D AcrySof ReSTOR IOL and 46 eyes implanted with the +4 D lens. Mean patient age was 63.5 years in the +3 D IOL group and 65.8 years in the +4 D IOL group. Axial length was statistically significantly longer in the +4 D IOL group (P = .027).

Inclusion criteria were age between 40 and 85 years, presence of senile cataract and motivation to achieve spectacle independence after cataract surgery.

Patients with preoperative corneal astigmatism exceeding 2 D, occupation requiring night driving, and significant ocular comorbidities such as abnormal cornea or iris, glaucoma, macular degeneration, retinopathy, uveitis, retinal detachment or neuro-ophthalmic disease were excluded.

“We feel that both patient selection and preoperative counseling are important factors in achieving high levels of patient satisfaction in this particular field of cataract surgery,” Dr. de Vries said.

Primary outcome measures were binocular corrected and uncorrected near, intermediate and distance visual acuities, preferred working distance, contrast sensitivity, straylight and wavefront aberrometry measurements.

Visual acuity, refraction and optics

Study results showed that binocular uncorrected intermediate vision was markedly better in the +3 D IOL eyes than in the +4 D IOL eyes at 40, 50, 60 and 70 cm. The improvement in intermediate vision was shown on a monocular defocus curve assembled by determining visual acuity with spectacle correction adapted in 0.5 D increments from –5 D to +2 D from the patient’s manifest refraction.

“The better intermediate vision for the +3 D model as compared to the +4 D model is demonstrated by the better visual acuity between the two ‘hilltops’ in the defocus curve, which represent the two nodal points of the IOL,” Dr. de Vries said.

Both IOLs yielded similar contrast sensitivity and intraocular straylight levels, Dr. de Vries and colleagues reported.

Preferred working distance for near tasks was 38.9 cm in the +3 D IOL group and 31 cm in the +4 D IOL group; statistically significant (P < .001).

“None of the +3 D subjects spontaneously mentioned problems with the increase in working distance for near, whereas difficulty with intermediate visual acuity — for example, computer work — used to be a complaint of some patients when only the +4 D model ReSTOR was available,” Dr. de Vries said. “We have been unable to formally compare this, since this was a nonrandomized study resulting in patients choosing the +3 D model when intermediate visual acuity was considered of prime importance for their personal situation.”

The +3 D IOL eyes had significantly less higher-order and spherical aberration than the +4 D eyes. Dr. de Vries attributed the difference to the +3 D IOL’s apodized central diffractive surface having nine concentric steps and the +4 D lens having 12 steps.

“This is of importance, since the levels of both higher-order aberrations and spherical aberrations have been associated with clinical results, notably contrast sensitivity, distance visual acuity and depth of focus, for both monofocal and multifocal IOLs,” Dr. de Vries said. “Differences between both models in vitro using an optical bench might further clarify optical differences between the +3 D and +4 D model.”

Dr. de Vries advised caution in comparing the aberrometry values of two IOLs.

“Aberrometry findings are the result of both corneal and IOL-related parameters,” he said. “Caution should therefore be exercised when comparing two IOLs with respect to aberrometry findings in patients, given that differences in corneal shape rather than differences in IOL design can influence measurements.” – by Matt Hasson

• Niels E. de Vries, MD, can be reached at Maasricht University Medical Center, Department of Ophthalmology, P. Debyelaan 25, 6202 AZ, Maastricht, The Netherlands; e-mail: niels.de.vries@mumc.nl.