Multifocal IOL a successful option

As medical monitor for the multicentre clinical investigation of a multifocal full-optic diffractive IOL (Tecnis, Abbott Medical Optics), and as a busy refractive cataract surgeon regularly implanting these lenses, I have developed an intimate understanding of this technology's strengths and weaknesses.¹

Having a strong knowledge base of expected outcomes will facilitate counselling prospective surgical candidates.

It's interesting that this satisfaction rate is very similar to that reported for LASIK: "The overall patient satisfaction rate after primary LASIK surgery was 95.4% (2097 of 2198 subjects; range of patient satisfaction for the 19 articles was 87.2% to 100%).² That 19 out of every 20 patients will be satisfied with the outcomes of surgery should provide some initial confidence to surgeons trying a new technology for the first time.

That's an exciting result, and it leads to an important question. If they are in the 12% wearing glasses, why and for what purpose?

One consideration is correction of astigmatism. In the FDA study, investigator-surgeons were not allowed to perform adjunctive procedures to correct astigmatism such as limbal-relaxing incisions (LRIs). The FDA has required this approach in every IOL study of which I am aware.

Another consideration is intermediate-range vision - computer distance. The optical design of the diffractive multifocal IOL produces a defocus curve with a saddle point at 67 cm (Figure 1). The distance from my eyes to my laptop screen is 67 cm. For subjects with a 4 mm pupil, the visual acuity at that distance dipped to 20/40. Those with small pupils did better: about 20/25 with a 2.5 mm pupil.

I find, in clinical practice, that patients who receive this multifocal lens often notice a soft focus at computer distance, especially in the first few days to weeks after surgery. I have had patients move their monitors closer, or push them back to the far edge of their desks, to improve the crispness of the screen. Fortunately, at the 6- to 8-week point, almost all of these people find a comfortable working distance for computer use (and it's usually right back where it was prior to surgery). I have found this gradual progressive improvement of intermediate range vision to be consistent and predictable.

Accuracy to target for IOL power calculation and reduction of astigmatism remain the keys to achieving success with this lens. Using the IOL Master, EyeSys Topographer, and Holladay 2 formula, I am achieving 86% within ±0.5 D SEQ and a mean absolute error of 0.325 D. Using LRIs cut to 90% of pachymetry at the 10 mm optical zone and adjusted with the ORange intraoperative aberrometer, I am reducing mean preoperative keratometric cylinder from 1.31 to 0.44 D.³

The result is that 62% of my patients with binocular Tecnis multifocal lenses read uncorrected 20/20 at distance and 20/25 at near or better, and 80% read 20/25 at distance and 20/30 at near or better (this was true of 79.9% of 294 subjects in the FDA study).

Dysphotopsia - glare and halo - remain an issue with multifocal lens technology. With the Tecnis multifocal about 40% of subjects in the FDA study noticed halos at 4 to 6 months. Fortunately, this percentage drops to 22% by 1 year. Similarly, the percentage of subjects who described their halos as 'severe' dropped from 9% at 4 to 6 months to 5% at 1 year. The reduction in symptoms of dysphotopsia over time probably relates to neural adaptation. The important guidance for surgeons is to provide lots of reassurance, avoid the early YAG capsulotomy unless absolutely certain that the posterior capsule is the culprit, and spare the IOL exchange as long as possible. My own experience, over 15 years of multifocal IOL implantation, is that a handful of patients ultimately will decide that IOL exchange is the only solution. Also, in my experience, those who do opt for exchange are glad that they did.

In summary, this multifocal lens offers a successful option for achieving spectacle independence after cataract surgery. The new one-piece design and microincision injection system should inspire more surgeons to give this technology a try.

Dr Mark Packer is co-editor of Cataract Corner published in OT. He is associate clinical professor of ophthalmology at Oregon Health & Science Univeristy, Portland, Oregon, USA, and is in private practice in Eugene with Drs Fine, Hoffman and Packer. He is a consultant to Abbott Medical Optics.

References

1. M. Packer et al., Am. J. Ophthalmol., 2010; 149:577–584.e1. Epub 6 Feb 2010.

2. K.D. Solomon et al., Ophthalmology, 2009; 116:691–701.

3. M.Packer, J. Cataract Refract. Surg., 2010; 36:747–755.