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Up Front | Oct 2008

Accommodating Plus Diffractive Multifocal IOLs

Understanding the differences among the available presbyopia-correcting IOL designs permits an individualized approach.

The strengths and weaknesses of different presbyopia-correcting IOL designs are complementary in many respects. The growing interest in a mixing approach affirms that no available refractive IOL is perfect, and we are learning that many patients tolerate and achieve functional advantages with combinations of IOL styles.1

PRESBYOPIA-CORRECTING IOL OPTIONS
Until the diffractive Tecnis Multifocal (Advanced Medical Optics, Inc., Santa Ana, California) is approved by regulators in the United States, the aspheric apodized diffractive AcrySof Restor (Alcon Laboratories, Inc., Fort Worth, Texas) provides the strongest reading add of any presbyopia-correcting IOL available to US surgeons.1,2 The 50:50 distance:near split throughout the center of the lens provides good reading ability even with small pupil sizes. The higher near add allows a close reading distance, which is the habitual preference of many myopes. A close reading distance also increases the magnification of smaller print, but the tradeoff is having less light coming from intermediate distances.

With respect to mixing IOLs, the zonal refractive multifocal ReZoom (Advanced Medical Optics, Inc.) and the accommodating Crystalens HD (Bausch & Lomb, Rochester, New York) can potentially fill the gap in the intermediate range found with the aspheric Restor. With increasing dilation, the incoming distance:near light ratio of the Restor design increases dramatically; there is no diffractive component in the optic periphery. This significantly reduces the severity of nighttime halos compared with the ReZoom. Although Restor patients still notice halos and rings around lights, the severity is less compared with the zonal refractive Array (Advanced Medical Optics, Inc.; no longer available) and ReZoom.2

The Crystalens HD has an entirely different set of pros and cons. With emmetropia, near performance with the Crystalens is reduced and more variable compared with that provided by diffractive multifocal IOLs. However, particularly if the eye is left slightly myopic, uncorrected intermediate focus is typically good without the tradeoffs of halos and reduced contrast sensitivity.3

The ability to hit emmetropia with the Crystalens is less consistent because of an added variable; the effective lens position of a hinged IOL varies according to the sizes of the capsular bag and capsulorrhexis. However, refractive accuracy was improved with the broader haptics, larger optic diameter, and greater overall length of the 5-0 model, and the pseudoaccomodative range was noticeably improved with the recent Crystalens HD modification.

This technology is an excellent alternative for patients who desire and are accustomed to monovision and for those who are concerned about the risk of halos or diminished quality of vision at night. I also favor this choice if there is a possibility of decreased macular function (eg, in a patient following macular hole repair who nevertheless has a strong desire to reduce spectacle dependence). Generally, nighttime halos are of minimal severity with the Crystalens, and contrast sensitivity should be comparable to that of a spherical monofocal IOL.

MIXING PRESBYOPIA-CORRECTING IOLs
Currently, the biggest impetus for mixing IOLs seems to be for refractive lens exchange (RLE) patients who have much higher refractive expectations than senior citizens with cataracts. The latter group is usually thrilled with any IOL, and attaining good pseudoaccommodation is a surprising bonus for someone who lost accommodation 2 decades ago. My older cataract patients are usually so happy after their first surgery that they would question the notion of doing anything different for their second eye. Most of my cataract patients have the same presbyopia-correcting IOL in both eyes for this reason.

In contrast, the presbyopic RLE patient has excellent spectacle-corrected vision preoperatively and will be less forgiving of new optical aberrations and halos. They would not be considering expensive refractive surgery if they did not expect to be spectacle-free for most activities afterwards. Younger cataract surgery patients also have a different concept of presbyopia from senior citizens, and their refractive expectations are similar to those of RLE patients. Baby boomers are accustomed to having technology solve most problems, and they like to research which technology is the best. Those who spend many hours on the Internet researching which cell phone to buy usually feel that their IOL decision deserves the same careful analysis. They are more open to a mixing strategy to attain the complementary benefits that no single lens can provide.

Pairing a Crystalens HD in the dominant eye with a diffractive multifocal IOL, such as the aspheric Restor, in the nondominant eye is my preferred mixing strategy. Of the two, the diffractive multifocal provides better and more predictable near reading ability. On the other hand, the Crystalens HD provides better intermediate function and should provide better quality of vision at distance, particularly at night.

Staging the IOL decision makes particular sense if there is any question as to which IOL to choose. Both the patient and the surgeon can assess the functional result of the first eye implantation before deciding which IOL to implant in the second eye. For example, implanting a monofocal or accommodating IOL in the second eye can be an excellent fallback strategy for patients having trouble adapting to halos or aberrations from a multifocal IOL in their first eye. Such a contingency plan helps reassure patients preoperatively who are worried about being locked in to a multifocal that they may not tolerate well. Likewise, if a patient were disappointed with his reading ability following implantation of a Crystalens HD or ReZoom in one eye, a diffractive multifocal IOL, such as the aspheric Restor, can be implanted in the second eye.

UNDERSTAND THE DIFFERENCES
In the United States, the ability of surgeons to bill patients out of pocket for the refractive component of cataract surgery allows surgeons and patients to differentiate between the treatment of cataract and any optional refractive surgical goals. That we have no universally perfect IOL solution increases the importance of careful patient selection. Understanding the differences among the available presbyopia-correcting IOL designs permits us to individualize our approaches, which for some patients may include mixing different IOL technologies.

David F. Chang, MD, is a Clinical Professor at the University of California, San Francisco, and is in private practice in Los Altos, California. Dr. Chang states that he is a consultant to Advanced Medical Optics, Inc., Alcon Laboratories, Inc., and Visiogen, Inc., and he donates these consulting fees to the Himalayan Cataract Project. Dr. Chang may be reached at tel: +1 650 948 9123; e-mail: dceye@earthlink.net.

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