American Academy of Ophthalmology Web Site: www.aao.org
Ophthalmic Pearls: Cataract
When to Use Multifocal Intraocular Lenses
By Christopher P. Majka, MD, and Alan N. Carlson, MD
Cataract removal is the most common surgical procedure in the United States, with nearly 3 million operations performed annually. This number will likely grow, according to National Eye Institute statistics that predict an increase in the number of people in the United States with cataracts from the current level of 20 million to more than 30 million by the year 2020. This estimate is further supported by data from the Framingham Eye Study showing that the prevalence of cataracts increased with age from 4 percent in the 52 to 64 age group, to 50 percent in the 65 to 74 age group, to more than 90 percent in the 75 to 85 age group.
Cataract surgery with implantation of a traditional monofocal IOL, targeting distance vision, leaves most individuals dependent on some correction, usually spectacles, for near vision. Traditional strategies for these patients have included the following:
The newer IOLs that actively accommodate by changing optic position or shape through attempted preservation of ciliary body function have received mixed reviews with regard to the predictability of accommodative range and the longevity of effect; however, the principles involved offer the best opportunity for us to eventually establish a mechanism and outcome that most closely rivals the vision found in youthful emmetropes.
Recent advances in pseudoaccommodative multifocal IOL technology offer a new alternative for those desiring vision at both distance and near. In March 2005 the ReStor apodized diffractive IOL from Alcon and the ReZoom multifocal refractive IOL from Advanced Medical Optics both received FDA approval for capsular bag implantation following cataract surgery.1
ReStor Apodized Diffractive IOL
How does it work? The ReStor multifocal IOL uses three separate but complementary optical principles (refraction, diffraction and apodization) to achieve satisfactory near and far visual acuity. The refractive portion of the optic functions like a standard IOL, with the optic periphery dedicated to distance vision and designed to optimize night vision when the pupil dilates under scotopic conditions. The diffractive portion of the optic consists of 12 concentric rings on the anterior surface of the optic, and it is located within the central circle, which is 3.6 mm in diameter and is designed to provide distance and near vision in moderate to bright light. Apodization is the radial variation in optical properties that comes from decreasing the height of each concentric ring from the center toward the periphery of the optic surface (from 1.3 to 0.2 µm). This balances the amount of light energy that is distributed between distance and near as a function of pupil size, which improves the efficiency and effectiveness of the quality of near vision achieved and reduces problems with glare and halos. Ring location, spacing and variation of height serve within the pupillary aperture to provide a satisfactory near image at approximately 25 to 33 cm.
How is it used? The ReStor IOL is a foldable IOL designed for placement within the capsular bag at the time of phacoemulsification. It is injected using the Monarch B or C cartridge through the traditional phacoemulsification incision.
Side effects. The side effect profile of the ReStor multifocal lens is very similar to that of traditional monofocal IOLs. However, with the ReStor, there is a greater chance of having significant halos (5 percent of all patients) or glare (5 percent) compared with a monofocal lens (1 percent and 2 percent, respectively). The halos or glare were severe enough that in studies conducted for Alcon by independent consultants 0.5 percent of patients requested that their ReStor IOL be removed. Another side effect of the ReStor IOL’s complex optics is increased adjustment time compared with a monofocal IOL. Driving at night or reading in the evening under dim illumination may be more difficult due to qualitative vision changes compared with a standard IOL.
The interaction of the ReStor IOL with various ocular conditions including glaucoma and retinopathy has not been established.
ReZoom Multifocal Refractive IOL
How does it work? The ReZoom IOL is a refractive, distance-dominant multifocal optic that enables good vision through a range of distances. It is an improved version of the Array multifocal IOL that received FDA approval in 1997. The ReZoom lens uses five optical zones to focus light on the retina at all pupil diameters. This enables distance-dominant vision with a near add of 3.5 D in the plane of the IOL. (A usual spectacle add is 2 to 2.5 D, but when the lens is placed closer to the retina as an IOL, it must be more powerful.) In comparison with the 4 D of near add that the ReStor IOL provides, the ReZoom IOL offers a 3.5 D near add that results in a slightly longer working distance for reading vision.
Posterior capsular opacification can disrupt the complex optical properties of both types of multifocal IOLs, and a moderate amount of opacification has the potential for causing scattering of light that could be bothersome. The ReZoom lens is made of acrylic with a sharp-edged optic design to attempt to reduce the development of capsular opacification and thus maintain proper visual acuity.
The ReZoom IOL also attempts to reduce edge-related halos and glare, two of the more common complications of the earlier Array multifocal IOL, by using a triple-edge design. The anterior edge is rounded to reduce internal reflections, the side edge slopes to cut down on edge glare and the posterior edge is squared off to facilitate contact with the posterior capsule.
How is it used? The ReZoom is a foldable IOL designed for capsular bag placement following standard phacoemulsification cataract surgery, using a 3.2-mm posterior limbal incision centered on the axis of plus cylinder. Limbal relaxing incisions are safe, effective and predictable in the treatment of mild to moderate amounts of corneal astigmatism. This IOL is injected using the AMO Unfolder Implantation System.
Side effects. The most common concerns for ReZoom lens recipients include distance blur and monocular diplopia, as well as glare and halos at night. Potential solutions to these side effects include correcting residual astigmatism, treating a dry eye that might be worsening these effects and using the dome light in the car during night driving. Although many patients will adapt to these effects, the occasional patient may require implant removal for severe symptoms. In order to avoid the risk of significant side effects, it is advised not to implant the ReZoom IOL in patients with significant dry eye, corneal scarring, pupil size less than 2.5 mm, a monofocal implant in the first eye, uncorrected astigmatism greater than 0.5 D or unstable capsular support.
When using either the ReStor or the ReZoom IOL, the most successful cases will be patients who perceive their uncorrected reading vision to be a necessity rather than a mere bonus offered by new technology. Proper patient selection and education is the most important factor leading to eventual success, and patients identified as potentially prone to finding negative aspects of their vision quality after surgery should be excluded. Before making the commitment to surgery, patients requesting these IOLs based on marketing perceptions or what they have read on the Internet must be made aware of the sacrifice they might experience with the night glare and loss of contrast, which they could perceive as reduced distance quality. The properly selected patient will consider these sacrifices well worth the gain in uncorrected near vision.
Postsurgically, the mechanism by which both of these lenses works also makes vision degradation more apparent (than a standard IOL) when there is surface dryness, blepharitis, basement membrane dystrophy, corneal scarring, corneal edema, IOL tilt, decentration, posterior capsular opacification, macular edema, any residual refractive error or even astigmatism greater than 0.5 D. Although patients tend to adapt and perceive vision improvement over time, all of these variables should be searched for and corrected if possible in those patients experiencing slow or inadequate recovery. Patients are more accepting of this new technology when the second eye is treated. But second-eye surgery should be avoided until dissatisfaction with the first IOL is addressed.
Also, caution is recommended when it comes to mixing IOL technologies. There has been a recent trend to mix technologies when addressing patient dissatisfaction after first eye surgery and for those patients desiring different working distances for near tasks—but this increases the chance of patient dissatisfaction. Before surgery, patients tend to focus on the positives in anticipation of what they are going to get. Their focus shifts to perceived negatives after the surgery, and mixing IOL technologies allows patients to focus on unmet expectations when their two eyes are functioning differently.
The use of pseudoaccommodative multifocal IOLs as a potential treatment for presbyopia in patients without cataracts is currently under study. Using these IOLs in patients undergoing clear lensectomy does pose some risk as an intraocular procedure. There is an increased risk for retinal detachment in those patients with a long axial length. And there may also be greater risk of retinal detachment in phaco patients under the age of 50.2 At present, both lenses are considered “off label” for use in patients undergoing refractive lensectomy.
With the ReStor and ReZoom (and some other new lens technology), there is a financial cost to the patient, as these new presbyopia-correcting lenses are not fully covered by Medicare, Medicaid or most insurance companies.
In 2005, the Centers for Medicare & Medicaid Services agreed to increase reimbursement for the new technology multifocal IOLs to $200. However, that is insufficient to cover the cost of the ReStor ($895 per lens) and ReZoom IOLs (also $895 a lens), not to mention the costs associated with patient education, testing, follow-up care and potential surgical procedures needed for any patient who might have unacceptable refractive error following surgery. If patients want these lenses, they must pay the balance.
New technology, which now includes presbyopia treatment at additional patient expense, will continue to raise the bar of expectation for patients as cataract surgery with IOL implantation continues to be recognized as one of the most successful surgical procedures medicine has to offer.
1 Some information in this article was obtained from Alcon and Advanced Medical Optics, manufacturers of the ReStor and ReZoom IOLs.
Dr. Majka has completed a six-year accelerated BS/MD program at the Northeastern Ohio Universities College of Medicine, and will be training in ophthalmology at The Kresge Eye Institute in Detroit. Dr. Carlson is chief of the corneal and refractive surgery service at Duke University in Durham, N.C. Neither has a proprietary interest in the products or companies mentioned.