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No long-term differences between silicone, acrylic IOLs in phaco-trab
Lower incidence of PCO attributed to intensive corticosteroids.
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DETROIT — There are no significant long-term differences between silicone and acrylic intraocular lenses in patients who undergo primary trabeculectomy, phacoemulsification and posterior chamber IOL implantation, according to a study published in Ophthalmology.
“It is acceptable to use either the silicone or acrylic lens,” said lead author Michael D. Ober, MD, who conducted the study in collaboration with Dong H. Shin, MD, and other glaucoma research staff at the Kresge Eye Institute here. “Minor differences in posterior chamber opacification are not going to be significant in a combined cataract/glaucoma procedure, probably because of the intraoperative and postoperative routine of intensive corticosteroids to promote filtration,” Dr. Ober told Ocular Surgery News.
The study is an extended follow-up of a previously published trial that appeared in Ophthalmology in 1997. The earlier study was a 1-year prospective, randomized trial that compared silicone and acrylic IOLs. “That study actually showed a significant difference in the incidence of early postoperative IOP spikes,” said Dr. Ober, who is presently a resident at Weill Cornell Medical Center/New York-Presbyterian Hospital. “Postoperative intraocular pressures greater than 25 mm Hg and intraocular pressure spikes of more than 5 mm Hg above preoperative intraocular pressures were significantly greater in the acrylic group in the immediate postoperative period.”
The current study reports long-term outcomes of posterior capsular opacification (PCO) as well as filtration and visual acuity outcomes following phacotrabeculectomy with acrylic vs. silicone foldable IOL. The study enrolled a total of 200 eyes (102 silicone, 98 acrylic) of consecutive primary open-angle glaucoma patients. Adjunctive mitomycin C was used selectively, mostly in patients with one or more risk factors for filtration failure.
PCO incidence equal
“The main outcome of the new study was the incidence of posterior capsular opacification (PCO),” Dr. Ober said. “This was found to be equal between the two lens groups, despite silicone supposedly having a higher degree of PCO, according to some of the literature. Silicone is thought to be less biocompatible than acrylic and induce an inflammatory response.” However, there are many different factors that influence PCO. “We may have found equal results because of the heavy use of intraoperative and postoperative steroids,” Dr. Ober said.
The steroid regimen, identical for both groups of patients, consisted of intraoperative sub-Tenon’s injection of 40 mg depo-steroid and postoperative routine of a steroid antibiotic ophthalmic ointment at bedtime and 1% prednisolone acetate (one drop every 1 hour). “It has been shown in other published articles that using corticosteroids such as dexamethasone can decrease the migration of lens epithelial cells, which is a major cause of PCO,” Dr. Ober said.
The rate of PCO at 24 months in the acrylic IOL group was 17.1%, compared to 16.1% in the silicone group.
Because there is growing evidence to suggest that IOL design, materials, haptic configuration and positioning may influence PCO rates, the study compared two IOL models with similar features: the Iolab LI41U silicone foldable lens with PMMA haptics (Chiron Vision, Claremont, Calif.) and the Alcon AcrySof MA60BM acrylic foldable lens with PMMA haptics (Alcon Laboratories, Fort Worth, Texas). Both models have a biconvex contour, a 6.0-mm optic diameter and nearly identical overall lengths (12.5 mm silicone, 13 mm acrylic). And although the acrylic IOL has a larger degree of haptic flexion (10% vs. 5% for silicone), which exerts greater pressure on the posterior chamber, “this may be offset by the thinner overall width of an acrylic IOL with a greater refractive index,” Dr. Ober said.
Single medication favored
The investigators also assessed best-corrected visual acuity, intraocular pressure and number of pressure-lowering medications. “These were all found to be comparable among the two lenses,” Dr. Ober said. However, filtration success rates varied, although not significantly. “In the acrylic group, there was a trend toward improvement in patients on a single pressure-lowering medication without further surgical intervention,” he said. But for patients without any pressure-lowering medications, there was no difference.
Dr. Ober said both surgeon preference and ocular condition should dictate whether a silicone or acrylic lens is used. For example, “a surgeon may be less likely to use a silicone lens on a diabetic patient because of the potential for retina surgery in the future,” he said. In any event, “we believe that the judicious use of postoperative steroids helped to equalize the rate of PCO in the two groups of lenses. Our PCO rate compares very favorably to rates reported by other investigators.”
The researchers concluded that there are no significant differences in the long-term outcomes for PCO rate, visual acuity, IOP, medical dependency, and filtration success between the acrylic and the silicone foldable IOLs following phacotrabeculectomy. “Thus, the foldable IOL models used in our study are satisfactory choices for the great majority of glaucoma patients in need of combined glaucoma and cataract surgery,” Dr. Ober said.
For Your Information:References:
- Michael D. Ober, MD, can be reached at Department of Ophthalmology, Weill Cornell Medical Center, New York-Presbyterian Hospital, Starr F-826, 525 E. 68th St., New York, NY 10021; (212) 746-2444; fax: (212) 746-8870; e-mail: obermike@yahoo.com. Dr. Ober has no direct financial interest in any of the products mentioned in this article, nor is he a paid consultant for any companies mentioned.
- Ober MD, Lemon LC, Shin DH, et al. Posterior capsular opacification in phacotrabeculectomy: a long-term comparative study of silicone versus acrylic intraocular lens. Ophthalmology. 2000;107:1868-1873.
- Lemon LC, Shin DH, Song MS, et al. Comparative study of silicone versus acrylic foldable lens implantation in primary glaucoma triple procedure. Ophthalmology. 1997;104:1708-1713.