Chicago—Although the introduction of aphakic IOLs led to a 50-year epidemic of pseudophakic corneal edema, it is unlikely that the advent of phakic IOLs will cause history to repeat itself, said Joel Sugar, MD.
Chicago-Although the introduction of aphakic IOLs led to a 50-year epidemic of pseudophakic corneal edema, it is unlikely that the advent of phakic IOLs will cause history to repeat itself, said Joel Sugar, MD.
"The present regulatory process, postmarketing surveillance of approved implants, and ongoing research and development should prevent us from seeing problems of marked, ongoing endothelial cell loss and high rates of corneal decompensation in eyes with refractive phakic IOLs implanted," said Dr. Sugar, professor of ophthalmology and director, cornea service, University of Illinois at Chicago.
"Modification of lens design and placement led to less-distressing rates of cell loss with iris-supported lenses, and subsequent reports with the iris-claw implant and angle-supported lenses showed substantially better outcomes. Those recent data have led Dr. (Georges) Baikoff (of Marseille, France) to state optimistically that contemporary anterior chamber lenses with a safe design no longer cause anterior segment complications of corneal decompensation, cataract, glaucoma, and uveitis," Dr. Sugar said.
Because posterior chamber phakic IOLs are placed farther from the cornea, they have shown more promising safety than others. However, cell loss rates associated with that type of implant are not trivial, as indicated by one report of a 4% per year cell loss rate during the first 3 years postimplantation, Dr. Sugar noted.
"In evaluating the endothelial risks of phakic IOLs, it is important to know what is normal," Dr. Sugar said. "In adults, there is an average 0.6% decrease in cell density per year with aging, a 0.27 coefficient of variation in cell area, and 65% of cells are hexagonal."
He used those data for comparison as he reviewed findings from endothelial cell studies conducted as part of the safety analyses for the two phakic IOLs for myopia that have been presented for FDA review-the posterior chamber Visian (formerly known as the ICL, STAAR Surgical) and the iris-claw Verisyse (AMO; also, Artisan from Ophtec).
The data for the Visian IOL show rates of endothelial cell loss of 2.1% at 3 months, 3.3% at 1 year, 5.7% at 2 years, 8.9% at 3 years, and 9.7% at 4 years. Preoperatively, the coefficient of variation of cell size as well as the percentage of hexagonal cells was worse in the Visian lens recipients than in the normal population. However, both of those parameters improved with time, pointing to stabilization of cell loss.
"Those latter changes may reflect recovery from surgical trauma or recovery of cells altered by prior contact lens wear, but the bottom line is that in either instance, cell morphology improved and the rate of decline of cell density also appeared to taper," Dr. Sugar said.
Results from a consistent cohort of 57 patients followed over 4 years showed no cell loss between years 3 and 4 and perhaps even a slight gain in endothelial cell counts, although the change was not statistically significant, perhaps due to the small number of patients, he reported.
Three-year data from a consistent cohort of eyes that received the iris-claw Verisyse phakic IOL show decreases in cell density of 1.09% at 1 year and 3.8% at 3 years, for an average rate of cell loss per year of 1.27%.
The FDA review of the data from the two phakic IOL implants extrapolated the results to determine what the cell loss would be if the initial rate of change persisted.