By Laura J. Rongé, Contributing Writer
This article is from July/August 2005 and may contain outdated material.
In March, the FDA approved the AcrySof ReStor for cataract patients with and without presbyopia. How does this new multifocal IOL compare with other multifocal and accommodative lenses, such as the AMO Array (to be replaced eventually by the ReZoom IOL) and the Eyeonics CrystaLens? Does the new lens overcome previous limitations such as glare and halo around lights at night and loss of contrast sensitivity?
Diffractive Design
The AcrySof ReStor (Alcon) features a 6-millimeter optic that contains a central diffractive portion surrounded by a purely refractive portion.
The central 3.6 mm of the lens uses diffractive optics to divide its function into distance and near correction, with 50 percent of the light rays focused for each, explained Richard J. Mackool, MD, director of The Mackool Eye Institute and senior attending surgeon, New York Eye and Ear Infirmary. In the refractive periphery of the lens, beyond 3.6 mm from the center, the focal point is determined by the IOL power.
The central 3.6 mm of the lens contains diffractive grating. The largest diffractive step, located at the lens center, sends the greatest proportion of energy to the near focus. “As the steps move away from the center, they decrease in size, blending into the periphery and sending a decreasing proportion of energy to the near focus,” said David T. Vroman, MD, assistant professor of ophthalmology at the Medical University of South Carolina.
“When the pupil is small, such as during reading tasks, the lens provides excellent near and distance vision. In large-pupil situations, such as at night, the ReStor IOL becomes a distant-dominant lens,” said Dr. Vroman, who was an investigator in the Phase 3 FDA trial of the lens.
Efficacy Evaluated
The greatest advantage of the ReStor lens as compared with other multifocal, accommodative or pseudoaccommodative lenses is its efficacy, according to Dr. Mackool, who, as one of the principal investigators in the FDA trials, implanted ReStor lenses in 22 patients (43 lenses; 21 bilateral and one unilateral implantation).
In his study, every patient achieved BCVA of at least 20/25 at distance and at near. Of these patients, 19 were able to discontinue the use of spectacles for all distance, near and intermediate tasks. Three patients preferred to use glasses for reading small print. Dr. Mackool pointed out that these three patients had a residual refractive error, but treatment with a refractive procedure was deferred because of their participation in the FDA trial.
Even without secondary procedures to correct residual astigmatism or spherical refractive error, approximately 80 percent of the patients in the entire FDA study never used spectacles for distance, reading or intermediate tasks after having bilateral ReStor lens implantation, Dr. Mackool said. “Premarket approval data submitted for the Array and CrystaLens indicated that this most favorable result occurred in only 41 percent and 26 percent, respectively, of patients implanted with those lenses,” he added.
Intermediate Vision Questione
The design of the ReStor lens provides one focus at infinity and a second near focus at about 14 inches. There is no intermediate focus, and the defocus curve falls to 20/40 between the distance and near foci, explained Mark Packer, MD, clinical assistant professor, Oregon Health & Science University, Eugene.
“Intermediate vision is not as crisp as distance and near for some patients,” Dr. Vroman noted. “Rarely, a patient has requested glasses for the intermediate zone.”
Jorge L. Alio, MD, PhD, noted that intermediate vision with the ReStor lens is debatable. “Some surgeons find it inadequate and claim that this is a bifocal lens. In my opinion, intermediate vision is also pupil dependent,” he said. “My results with intermediate vision are good at this moment, and I do not have complaints from my patients concerning this.”
Dr. Alio is medical director, Vissum, Instituto Oftalmologico de Alicante in Spain, and vice chairman of the ISRS/ AAO executive committee. He has implanted the ReStor IOL in about 60 patients.
Comparing the ReStor to other lenses, Dr. Packer noted that the CrystaLens accommodating IOL provides excellent distance-corrected and uncorrected acuity at the intermediate range (32 inches), which is useful for computer work, shopping, dining out and magazine perusal. “On the other hand, many of the subjects in the FDA-monitored study of the CrystaLens wore a low-powered (+1.25) pair of glasses for prolonged reading,” Dr. Packer said.
The Array multifocal IOL features a refractive zone for intermediate-range vision, but it is the weakest of the zones, Dr. Packer reported.
Adjustment Period
Studies of the Array lens suggest that patients need approximately three months following bilateral implantation to adapt to the multifocal optical system, Dr. Packer reported. “We don’t know yet if a similar period of adjustment will be the rule with the ReStor, but it is probably prudent for surgeons to tell patients about a possible adjustment period,” he said.
Drs. Mackool and Vroman noted that the ReStor lens does not seem to require a neuroadaptation process. “Patients begin to function normally within 24 hours,” Dr. Mackool said.
Glare, Halo and Opacification
Any multifocal lens, whether refractive like the Array or diffractive like the ReStor, will produce a halo or blur circle around point sources of light, Dr. Packer said.
The design of the ReStor helps to minimize the halo effect but does not eliminate it, Dr. Packer said.
Dr. Alio’s patients do have some halos at night. “However, these halos are much less frequent and less troublesome than with the other multifocal lenses,” he reported. “This is especially noteworthy in high positive corrections, in which other diffractive technologies usually lead to a lot of night visual phenomena. The ReStor IOL has proven to be a good lens to replace other previously implanted multifocal lenses that have failed because of night photic phenomena,” Dr. Alio said.
All patients should be advised that there is a small chance that they may experience significant nocturnal halos after implantation, Dr. Mackool said, and if the problem is severe, IOL exchange to a monofocal lens within one month should be considered. After this time, he said, removing the first IOL and placing the second IOL within the capsular bag can be difficult.
The design and material of the AcrySof IOL has an excellent track record and the lens is easy to implant with the Monarch injector, Dr. Vroman said. “The truncated lens has been shown to have a low rate of posterior capsule opacification. If PCO does occur, a YAG capsulotomy would not alter the function of the lens.” He pointed out that, unlike accommodating lenses, the ReStor does not require movement to function, so there will be no concern about PCO affecting the accommodating effect of the lens.
Candidates and Consideration
Ideal candidates should have normal, otherwise healthy eyes with no macular degeneration or diabetic issues, Dr. Vroman said, and these patients should be highly motivated in seeking spectacle independence.
Spectacle dependence. Those patients with the most dependence on spectacle correction (poor distance and near acuity) would obviously benefit the most, Dr. Mackool added. “As with other multifocal and accommodative IOLs, presbyopic hyperopes will be great candidates. The plano presbyope or low myope will be tougher to please, simply because they already enjoy a good deal of spectacle independence,” Dr. Packer said.
Axial length. Dr. Mackool does not offer the refractive lens exchange procedure to men with an axial length of 25 mm or greater. “We have performed retrospective studies on these axially myopic men, between 20 and 60 years of age, and found that during the first three years after cataract-implant surgery they have a retinal detachment rate of approximately 5 percent. This is much greater than in any other group of patients undergoing cataract-implant surgery. We found that the rate of retinal detachment for women with an axial length of 25 mm or greater was approximately 0.3 percent,” he said.
Astigmatism. Patients should have less than 2.5 D of corneal astigmatism before surgery, and astigmatism should be corrected during the lens surgery procedure, Dr. Alio pointed out. “We cannot correct more than 2 to 3 diopters of astigmatism with limbal relaxing incisions. Even if we perform LASIK correction later, these patients are left with some aberrations that preclude the optimal use of the ReStor lens,” he explained.
Education. In educating patients, “Surgeons should inform patients about the potential loss of contrast sensitivity and the possibility of increased halo or glare symptoms at night,” Dr. Vroman said. “Patients who work, drive or fly at night may not want this lens.” Dr. Packer added that patients with exacting visual demands, such as engineers, artists and architects, should be “approached with caution.”
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Dr. Alio has no financial interests. Dr. Mackool is a consultant to Alcon and participated in the ReStor clinical trials. Dr. Packer has received travel, research and honoraria funds from Eyeonics and Alcon. He has done consultant work for Advanced Medical Optics. Dr. Vroman participated in the FDA trials of the ReStor lens.