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All current IOL options for presbyopia correction involve some compromise, according to one ophthalmologist.
Mannheim, Germany-All current IOL options for presbyopia correction involve some compromise, according to Michael C. Knorz, MD.
"In experience in Europe, up to 25% of patients with the ReZoom IOL implanted bilaterally had to wear reading glasses," he said. "This is unacceptable for a procedure that patients undergo with the goal of getting rid of their glasses."
Another multifocal IOL (Tecnis, AMO) has a diffractive aspheric optic that provides good distance vision and excellent near vision. However, because it has a +4-D add, near focus is very close and intermediate vision is only moderate.
"For many patients, intermediate vision is not good enough to allow them to work at their computer without glasses," Dr. Knorz said.
Another aspheric diffractive multifocal IOL (AcrySof ReSTOR, Alcon Laboratories) originally was introduced with a +4-D add. The lens provided visual function results similar to that of the Tecnis multifocal IOL, with good distance vision, excellent near vision, and intermediate vision that was insufficient in many patients. However, a redesign featuring a +3-D add moves the near focus further out so that compared with the +4-D version of the ReSTOR IOL, patients now can read comfortably with material held a few inches farther from the face and also have improved intermediate vision.
"In a study published in 2009 [Alfonso et al. J Cataract Refract Surg. 2009;35:885-892], patients with the +3-D add aspheric ReSTOR IOL [implanted] achieved uncorrected visual acuity of 20/40 or better at all distances," he said.
Dr. Knorz also discussed patient selection criteria for multifocal IOLs. Patients with presbyopic hyperopia represent the best candidates, and success generally is achieved in those with presbyopia with high myopia (> –6 D). However, emmetropic patients undergoing cataract surgery may be more difficult to satisfy and patients with low myopia are poor candidates.
"Regardless of their refractive error, all patients who are considering a multifocal IOL need to understand that they will be sacrificing a little bit of distance vision and must accept the occurrence of such side effects as halos at night in exchange for reduced spectacle dependence," Dr. Knorz said. "Patients can be counseled that the halos should become less obvious with time, but will probably not disappear entirely. If these trade-offs are not acceptable, patients should not get a multifocal IOL."
He added that patient education software (IOL Counselor, Patient Education Concepts Inc./Eyeland Design Network GmbH) can be used to help patients appreciate the visual effects of presbyopia, cataracts, and multifocal versus monofocal IOLs.
The latest version of an accommodating IOL (Crystalens HD, Bausch & Lomb) represents a new design with a central optic modification that induces spherical aberration to increase depth of field for improved near vision function.
A dual-optic accommodating IOL (Synchrony, AMO) is CE marked but not yet approved by the FDA. A first published clinical study [Ossma et al. J Cataract Refract Surg. 2007;33:47-52] reporting on 24 eyes with the dual-optic accommodating IOL implanted showed that based on defocus testing, a mean accommodative range of 3.2 D was achieved at 6 months.
However, another study using dynamic stimulation of accommodation showed only 1 D of accommodative amplitude at 54 months [Ehmer et al. J Cataract Refract Surg. 2008;34:2024-2029].
Dr. Knorz also mentioned that the distance performance of different multifocal and accommodating IOLs recently was compared through optical bench testing [Maxwell et al. J Cataract Refract Surg. 2009;35:166-171] using modulation transfer function measurements and the U.S. Air Force 1951 Resolution Target. Results showed greater contrast loss at distance with the ReZoom multifocal IOL relative to the Crystalens AT-50SE accommodating IOL.
FYIMichael C. Knorz, MD
Dr. Knorz is a consultant to and lecturer for Abbott Medical Optics, Alcon Laboratories, Optical Express, and Technolas Perfect Vision.