After bilateral cataract surgery, patients implanted with multifocal intraocular lenses (IOLs) were more likely to be spectacle-independent but also to undergo IOL exchange than those with monofocal lenses, according to findings of a randomized, multicenter clinical trial published online September 24 in Ophthalmology.
"Patients receiving monofocal IOLs with the powers of the lenses set to give clear distance vision are very likely to require reading glasses," lead author Mark R. Wilkins, MD, FRCOphth, consultant ophthalmologist, Moorfields Eye Hospital, London, United Kingdom, told Medscape Medical News. "In contrast, multifocal IOLs allow distance and near vision without glasses but...are more likely to produce glare symptoms."
The UK National Health Service only offers monofocal, or fixed-focus, IOLs to patients having cataract surgery, Dr. Wilkins explained. Multifocal IOLs are available privately, but even insured patients have to pay for the extra cost of the multifocal IOLs.
"When implanting monofocal IOLs, it is possible to adjust their powers to produce monovision, where one eye is set for distance and the other eye is set for near," Dr. Wilkins said. "We wanted to find out if monovision...achieved the same level of spectacle independence as...multifocal IOLs."
Before bilateral sequential cataract surgery, 212 patients with bilateral, visually significant cataract were randomly assigned 1:1 to receive bilateral Tecnis ZM900 diffractive multifocal lenses (Abbott Medical Optics) or Akreos AO monofocal lenses (Bausch & Lomb) with the powers adjusted to target −1.25 diopters (D) monovision.
The main study endpoint was spectacle-independence 4 months after surgery on the second eye, and secondary endpoints included questionnaires (VF-11R, dysphotopsia [glare] symptoms, and patient satisfaction). Other visual function outcomes measured 4 months after the second surgery were near, intermediate, and distance logarithm of minimum angle of resolution (logMAR) visual acuity, stereoacuity, contrast sensitivity, and forward light scatter.
Spectacle Independence Better With Multifocal IOLs
Of 212 participants, 187 (88%) returned for 4-month postoperative evaluation. In the monovision group, uniocular distance refractions showed a mean spherical equivalent of +0.075 D in the distance eye and −0.923 in the near eye. Mean distance spherical equivalents in the multifocal group were −0.279 D in the right eye and −0.174 D in the left eye.
Spectacle-independence (reporting never wearing glasses) occurred in 24 (25.8%) of 93 patients in the monovision group and 67 (71.3%) of 94 patients in the multifocal group (P < .001; adjusted odds ratio, 7.51; 95% confidence interval, 3.89 - 14.47).
Binocular uncorrected acuities did not differ significantly for distance (0.058 logMAR for monovision vs 0.076 for multifocal; P = 0.3774). However, the multifocal group had significantly worse intermediate acuity (0.149 vs 0.221; P = .0001), and the monovision group had significantly worse near acuity (0.013 vs −0.025; P = 0.037).
Adverse events were more common in the multifocal group, with 13 patients having an IOL exchange during the primary surgery because of IOL damage during injection. However, Abbott Medical Optics has since switched from the 3-piece silicone optic design used tin this study to a 1-piece acrylic IOL.
In the first postoperative year, no patients in the monovision group underwent IOL exchange. In contrast, 6 patients (5.7%) in the multifocal group underwent IOL exchange, 4 of which were bilateral and 2 unilateral exchanges.
"Patients receiving Tecnis ZM900 multifocal IOLs were much more likely to report being spectacle-independent than those randomized to monovision using the Akreos AO IOL," Dr. Wilkins said. "The increase in spectacle independence came with an increased risk of intolerable glare symptoms. In the first year after surgery, 6 out of 112 patients receiving a multifocal IOL, [but none of the monovision patients,] underwent IOL exchange, mainly because of glare symptoms."
Glare was reported by 79% of patients receiving multifocal lenses and by 56% of those receiving monovision lenses (P = .001). Even though glare symptoms can contribute significantly to patient dissatisfaction, both groups of patients in this study had similar levels of overall satisfaction.
"Basically, the trade-off for an increased chance of spectacle-independence is reduced visual quality and a 1 in 20 chance of a further operation with some morbidity attached," Gerald Sutton, MBBS, MD, from the Sydney Medical School Foundation, professor of corneal and refractive surgery, Save Sight Institute Sydney University, Australia, told Medscape Medical News when asked for independent comment. "Stereopsis was better in the multifocal group, although the data were not presented; contrast sensitivity was better in the monovision group; intermediate distance was better in the monovision group; near vision was better in the multifocal group; and distance vision was equivalent."
Study Strengths and Limitations
"[This was] a well-designed, randomized controlled trial comparing multifocal and monovision strategies to reduce post–cataract surgery spectacle-dependence," Dr. Sutton said. "The study is prospective, the power of the study is high, and the conclusions are reasonable based on the data collected."
Because the study was conducted at government-funded teaching hospital clinics, the findings may not be generalizable to private practice. Limitations noted by Dr. Sutton were that the target for monovision was −1.25, but the final near target was −0.98.
"The study only gave patients 1 D of monovision [difference in prescription between eyes]," Dr. Wilkins agreed. "Studies with more monovision might achieve higher spectacle-independence."
Dr. Sutton wondered why there was no discussion regarding reduced contrast sensitivity, which is significant in patients who develop age-related macular degeneration (ARMD).
"All multifocal IOLs, by their nature, reduce modulation transfer function, and the major long-term concern with them is that they will further impair the function of an eye that subsequently develops ARMD," Dr. Sutton said. "The follow-up time of 4 months probably didn't allow for complete neuroadaptation that occurs in patients with multifocal IOLs. There was also no apparent attempt to work out the dominant eye. I think the explanation that this is difficult in patients with cataracts is a little weak, as is the assumption that all patients can 'adapt.' "
In terms of future research, Dr. Sutton recommended trials of better multifocal IOLs, genuine accommodative IOLs, and the "best" target refraction for monovision.
"Newer multifocal IOLs such as Zeiss Trifocal may perform better at intermediate range," he concluded.
Unrestricted grants from Abbott Medical Optics and Bausch & Lomb funded this study, which was supported in part by the UK National Institute for Health Research Biomedical Research Centre in Ophthalmology at Moorfields Eye Hospital and the University College London Institute of Ophthalmology. The authors, Dr. Sutton, and Dr. Wilkins have disclosed no relevant financial relationships.
Ophthalmology. Published online September 23, 2013. Abstract
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Cite this: Multifocal IOLs May Improve Vision but Need Replacement - Medscape - Oct 09, 2013.