Phakic intraocular lenses: Which lens when?

Chicago-All phakic IOLs (PIOLs) provide excellent predictability and efficacy along with the benefit of rapid visual recovery, but the posterior and anterior chamber models each have their own pros and cons.

"The ICL lies farthest from the endothelium centrally and in the periphery, and long-term safety data show no risk of causing endothelial decompensation with this PIOL," Dr. El-Danasoury said.

He observed that long-term stability is an issue for the iris-fixated PIOLs (Artisan/Verisyse and Artiflex/Veriflex, Abbott Medical Optics) and also for the angle-supported AcrySof Cachet (Alcon Laboratories), and this has consequences for safety and efficacy.

"If the haptic of the iris-fixated PIOL pierces the iris, which is not uncommon, the lens position will be unstable with the potential for endothelial damage and refractive change," Dr. El-Danasoury said. "We also know the AcrySof Cachet is not always stable because there are case reports describing its rotation. Any moving object in the anterior chamber is not welcome because it can lead to endothelial damage."

He added that the relatively soft hydrophobic acrylic material of the AcrySof Cachet PIOL predisposes to contact between the lens and the endothelium if the patient rubs the eye.

Reviewing endothelial safety data, Dr. El-Danasoury reported that in a published study [Ophthalmology. 2009;116:1314-1321] the mean endothelial cell loss rate at 1 year after implantation of the AcrySof Cachet PIOL was reported as 4.7%. However, while this average rate is acceptable, the data also showed a large standard deviation of 8% and a rate exceeding 10% in 15% of eyes. For the iris-fixated IOL, there has been huge variation in reported changes in endothelial cell counts with ranges between a gain of 34% and a loss of 15%.

In addition to greater endothelial safety, the more posterior position of the ICL confers superior cosmesis compared with anterior chamber PIOLs as well as better quality of vision because the implant lies closest to the nodal point and has a wider effective optical zone, Dr. El-Danasoury said.

He acknowledged that cataract has been reported at a rate of up to 0.5% of eyes with the ICL implanted, with risk factors being older age (>42 years) and extreme myopia (>14 D). More recently, use of very- high-frequency ultrasound biomicroscopy for sulcus measurement has enabled better ICL sizing, and better reproducibility has been documented in the vault and position of the lens with the potential for reducing the risk of cataract.

"Rate of cataract development with the current model (V4) ranges is very low and is believed to decrease with the newer model (V4b) that has penetrating holes to improve aqueous circulation around the implant. It is worth saying that in the worst-case scenario, cataract can be easily and successfully managed if it occurs," Dr. El-Danasoury said.