One of the drawbacks of IOLs as a replacement for the human crystalline lens has been the fixed focus of the IOL. Surgeons have had to ask their patients whether, after cataract surgery, they would prefer to see up close or in the distance without glasses. To address this issue, multifocal IOLs that provide refractive correction for both near and distance vision are available.
The original multifocal IOL concept was based on the principle that the pupil tends to constrict for near tasks, so the central portion of the lens was designed for near and the outer portion for distance. The obvious disadvantage is that distance correction is not available when bright lights constrict the pupil. Present designs address this problem by having central and outer zones for distance correction and intermediate zones for near. Other designs are supposed to move anteriorly with accommodative effort to allow near focusing. A combination of geometric optics and diffraction optics can also achieve a multifocal effect. The long-term effects of multifocal lenses are under investigation. The FDA has approved the following multifocal lenses for use in the United States:
AcrySof ReSTOR (Fig 8-40) (Alcon, Ft Worth, TX) uses a central series of blended diffractive zones (apodized diffractive surface) designed to focus light from distant, intermediate, and near objects. Surgeons have reported that patients have acceptable distance and near vision with this lens, although intermediate vision may be less acute.
ReZoom (Fig 8-41) is a multifocal aspheric refractive IOL that distributes light over 5 optical zones to provide near, intermediate, and distance vision. Its manufacturer, Advanced Medical Optics, brought the first multifocal IOL (Array) to the US market in the mid-1990s. The ReZoom lens, a second-generation multifocal, was approved by the FDA in March 2005. Surgeons have reported that patients have acceptable distance and intermediate-range vision with this lens.
Crystalens (Fig 8-42) (Eyeonics, Inc, Aliso Viejo, CA) gained FDA approval in late 2003. The lens optic is attached to supportive flanges. Each flange has a “hinge” designed to allow the optic to move anteriorly with accommodative effort and to move posteriorly with accommodation relaxed. Patients have reported variability in achieving emmetropia and satisfactory accommodative range.
The advantages of these lenses include an increased range of vision with reduced dependence on glasses. The drawbacks of multifocal IOLs include reductions in contrast sensitivity and best-corrected visual acuity and the presence of glare and halos (see also BCSC Section 3, Clinical Optics). More “chair time” needs to be spent counseling these patients. Multifocal IOLs require very accurate biometry and IOL power calculations, and they may work best when implanted bilaterally in patients with minimal astigmatism. Patients with hyperopia may be less bothered by some visual aberrations than are patients with myopia. It is strongly recommended that a special consent process be used with this technology. The surgeon should have a strategy in place for managing postoperative residual refractive errors, including possible IOL exchange, performed preferably before capsular fibrosis increases the difficulty of explantation.
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