Which multifocal to use depends on patient’s needs
With no universally perfect choice, knowledge of each IOL’s characteristics is necessary to guide patient selection.
Patient selection would be much easier if we had a powerful accommodating IOL. Optical quality would not be compromised by nighttime halos or reduced contrast sensitivity. Patients could dynamically shift their focus along a continuous range of distances from far to near. The deciding factor would simply be the patient’s desire and willingness to pay for this convenience.
Although much improved, multifocal IOLs will always fall short of these lofty goals, and compromise, both in terms of optical quality and pseudoaccommodative performance, will be inherent in their design. Therefore, proper patient selection becomes critical, and our expertise in this area is a big part of the premium cost of the procedure.
The optical differences in the design of the AcrySof ReSTOR (Alcon) and the ReZoom (Advanced Medical Optics) IOLs should be well-understood by refractive IOL surgeons. Eyes with high or irregular astigmatism, maculopathy or reduced vision potential, and zonular problems predisposing to IOL decentration are poor candidates. However, assuming that an interested patient is a good multifocal candidate, each design has pros and cons. It is our job to determine the best match for each patient.
The central distance-only zone of the ReZoom makes this multifocal “distance-dominant” with normal pupil sizes. This means that uncorrected reading vision is poor through small pupils, and patients read better if lighting is reduced enough to avoid miosis.
David F. Chang
Although halos are less severe than with the Array (Advanced Medical Optics), they are still noticeable to patients whenever the pupil dilates widely, such as in younger patients at night. The ReZoom has a lower near add (+2.6 D) than the ReSTOR (+3.2 D). In addition, the blending of the ReZoom’s refractive zones creates a progressive add, which devotes some focus to intermediate distances. However, having more light coming from distance and intermediate points reduces the near performance of the ReZoom when compared with the ReSTOR.
The zonal refractive design seems to make this technology slightly more forgiving of being ±0.5 D hyperopic or myopic. Distance contrast sensitivity should be reduced less than with the ReSTOR because the central 2-mm zone essentially functions like a monofocal distance lens. In addition, there is no loss of incoming light with the zonal refractive optic.
The apodized diffractive design of the ReSTOR provides excellent near and distance function, despite the loss of some incoming light due to diffractive scattering. The 50:50 distance/near split throughout the center of the lens provides good reading ability, regardless of pupil size. The higher near add allows a closer reading distance, which is the habitual preference of many myopes. A closer reading distance also increases the magnification of smaller print, but the tradeoff is having less light coming from intermediate distances.
With increasing dilation, the incoming distance/near light ratio increases dramatically due to the ReSTOR’s design (no peripheral diffractive optic). This significantly reduces the severity of nighttime halos, compared with the ReZoom. Although ReSTOR patients still notice halos, severe complaints are rare, in my experience.
Pupil centration is important with a diffractive optic in order to avoid coma and other aberrations. Because the pupil is usually decentered nasally, I have found that orienting the ReSTOR haptics from 6 o’clock to 9 o’clock and slightly nudging the IOL nasally improves the centration of the diffractive pattern. Paulo Vinciguerra, MD, has suggested this strategy based upon improved wavefront scans and decreased patient complaints in eyes in which he re-positioned the ReSTOR because of symptomatic decentration with the pupil.
The crystalens (eyeonics) has a different set of pros and cons compared with multifocal IOLs. With emmetropia, near performance is reduced and is more variable compared with both the ReSTOR and the ReZoom. However, intermediate focus is good without the tradeoff of halos and reduced contrast sensitivity. The ability to hit emmetropia is less consistent because of an added variable – the effective lens position of a hinged IOL will vary according to bag and capsulorrhexis size.
The crystalens is an excellent alternative for those patients who desire and are accustomed to monovision and are concerned about the risk of halos. I also favor this choice if there is a possibility of decreased macular function (eg, a patient following macular hole repair who nevertheless has a strong desire to try to reduce spectacle dependence).
Based upon these observations, I tend to choose the ReSTOR for patients with smaller or larger pupils, or if the patient frequently drives at night. The ReSTOR is more likely to satisfy the reading expectations of myopes, who tend to read fairly close without glasses and are unaccustomed to having good uncorrected intermediate vision. The ReZoom works well for hyperopes and taller patients with longer arms, for whom intermediate vision is important. Hyperopes usually do not hold reading material close to their faces and have lower expectations for reading ability. Emmetropia is less consistently attained in higher hyperopes, and the ReZoom is more forgiving of slight ametropia. Currently, only the ReZoom is available in low diopter powers.
Patients with early macular degeneration are not good multifocal candidates because they would be less likely to reap the benefits. However, it is not clear how adversely multifocal IOLs might affect such patients because the higher add when donning reading glasses might function as a low vision aid. Nonetheless, when using reading glasses, there should be less contrast sensitivity loss with the ReZoom compared with the ReSTOR if a patient later develops macular degeneration.
Based upon these guidelines, the bilateral ReSTOR matches the profile for more of my refractive IOL patients than the bilateral ReZoom. I have performed a prospective study comparing the clinical and real-life experiences of 15 consecutive patients bilaterally implanted with the ReSTOR and 15 consecutive patients bilaterally implanted with the ReZoom. Multifocal IOL selection was not randomized but was determined based upon what I thought would best match the patient’s needs. Both groups performed well without glasses and had high satisfaction scores. The ReZoom gave slightly better distance performance, and the ReSTOR was superior at near. Although the incidence of halos was similar in both groups, they were more severe in the ReZoom group. Because of halos, one ReZoom patient required an explantation, and another chose to indefinitely postpone cataract surgery in his second eye.
Mixing ReSTOR and ReZoom
As pointed out by Frank Bucci, MD, Richard L. Lindstrom, MD, and others, the strengths and weaknesses of these two multifocal designs are complementary in many respects. The ReZoom can fill the intermediate gap found with the ReSTOR. The ReSTOR provides a stronger reading add and allows reading with smaller pupils under brighter illumination. The ReZoom probably provides better contrast sensitivity in the distance, while the ReSTOR can make it easier to suppress the nighttime halos from the ReZoom eye. Pairing a crystalens (which is better for intermediate than near distances) with a ReSTOR lens is another possible strategy. Just as monovision is well-tolerated by some and not by others, it is unclear how many patients might find the asymmetry of this strategy bothersome. For this reason, many surgeons are understandably cautious about this approach.
In general, older cataract patients who have required spectacles for many years are less demanding as refractive patients. They are usually extremely happy with bilateral multifocal IOLs and would question the need to do anything different after a successful procedure on the first eye. Most of my patients have the same multifocal IOL in both eyes for this reason.
Refractive lens exchange patients and young cataract patients who have been relatively spectacle-free have much higher refractive expectations. I am more likely to offer these patients the option of mixing multifocal IOLs. Although it might make sense to implant the ReZoom in the dominant eye, I usually start with whatever IOL I would choose to use bilaterally. The patient can then decide to have the same or a different IOL implanted in the second eye based upon their evaluation of the first eye result. For example, if the patient is significantly bothered by haloes with a ReSTOR in the first eye, we can implant a crystalens in the second eye, which will improve nighttime symptoms and should augment intermediate focus.
The premium IOL channel appropriately allows surgeons and patients to differentiate between cataract treatment and optional refractive surgical goals. That we have no universally perfect solution increases the importance of careful patient selection. Understanding the differences between the available presbyopia IOL designs permits us to individualize our approach, which for some patients may include mixing different lenses.
For more information:
- David F. Chang, MD, is a clinical professor at the University of California, San Francisco. He can be reached at 762 Altos Oaks Drive, Suite 1, Los Altos, CA 94024; 650-948-9123; fax: 650-948-0563; e-mail: email@example.com. Dr. Chang is a consultant for AMO, Alcon and Visiogen.