There are three main types of phakic intraocular lenses (pIOL): those secured in the anterior chamber angle, those secured to the iris, and those placed between the crystalline lens and the iris. The latter two types are approved by the US Food and Drug Administration for use in the United States. Of note, an angle-supported pIOL (Vivarte) was withdrawn from the French market by the French Health Products Safety Agency in 2006 due to excessive corneal endothelial cell loss.[1]
pIOLs have advantages over corneal refractive surgery, including rapid visual recovery, minimal risk for corneal haze or ectasia, ability to treat high refractive errors, and less loss of contrast sensitivity. Among their disadvantages are corneal endothelial cell loss, cataract formation, glaucoma, iritis, pupil ovalization, and, of course, all of the other risks of intraocular surgery, including endophthalmitis.
Jonker and colleagues[1] looked at long-term endothelial cell loss in iris-supported pIOLs (iris-clip Artisan; Ophtec B.V.; Groningen, Netherlands) for myopia and myopic or hyperopic astigmatism. Three hundred eighty-one eyes received myopic pIOLs; 51% were seen at 5 years and 33% were seen at 10 years. One hundred twenty-six eyes received astigmatic pIOLs; 32% were seen at 5 years and 16% were seen at 10 years. While these follow-up numbers are certainly not ideal, the study does have some strengths, particularly that all of the procedures were performed by one surgeon and all of the endothelial cell density (ECD) measurements were performed using the same specular microscope.
I was somewhat surprised that the researchers did not find a significant acute decrease in ECD from preoperatively to 6 months postoperatively. However, I was not surprised that they found a chronic decrease in ECD over and above what is expected physiologically (0.6% per year); from 6 months to 5 years is 5.2% and from 6 months to 10 years is 10.9% in the myopic pIOLs. They found an even greater decrease in ECD in the astigmatic pIOLs, of 7.5% from 6 months to 5 years and 15.8% from 6 months to 10 years, after correcting for physiologic decrease in ECD.
It's important to note that the decrease in ECD for both pIOLs was linear over the entire 10-year period, with no evidence of stabilization. The primary risk factor for endothelial cell loss was shallower anterior chamber depth. In total, the authors removed 6.0% of myopic pIOLs and 4.8% of toric pIOLs due to excessive endothelial cell loss.
A recent American Academy of Ophthalmology Task Force suggested that one endpoint for research on new pIOLs is to determine the number of eyes with ≥ 25% decrease in ECD at 3 years.[2] The French Health Products Safety Agency guidelines describe an ECD of < 1500 cells/mm2 as an indication for pIOL explantation.[3] Both seem like very high degrees of endothelial cell loss to me.
The mean age at the time of pIOL implantation in this study was 41 years in the myopia group and 39 years in the astigmatism group. Using the data from this study and assuming the need for a minimum ECD density of > 1500 cells/mm2 at the time of expected cataract surgery, they calculated the mean need for a preoperative ECD of at least 2215 cells/mm2 for the myopic group and at least 2616 cells/mm2 for the astigmatic group. However, for an 18-year-old patient, they calculated the need for a minimum ECD of 3310 cells/mm2 for the myopic group and 3885 cells/mm2 for the astigmatic group.
All of these numbers are above the minimums commonly recommended for the use of these lenses. The authors propose forming an international working group to establish guidelines for the degree of endothelial cell loss that warrants pIOL explantation. While they are at it, they may want to look into higher minimum ECD for placement of these lenses, especially in younger patients.
While pIOLs can be life-changing for many patients, surgeons and patients need to understand that these patients need to be followed on an annual basis to decrease the chances of corneal decompensation.
Medscape Ophthalmology © 2018 WebMD, LLC
Any views expressed above are the author's own and do not necessarily reflect the views of WebMD or Medscape.
Cite this: Christopher J. Rapuano. Endothelial Cell Density After Iris-Fixated Phakic IOL - Medscape - Aug 24, 2018.
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