PHAKIC IOLS

Several currently available phakic intraocular lenses (IOLs) generally provide excellent short-term safety and refractive outcomes in moderate to high myopia patients, Rudy MMA Nuijts MD, PhD told the 2013 ESCRS Congress in Amsterdam. These include iris- and angle-supported anterior chamber lenses and posterior chamber designs.

In addition to reversibility, phakic IOLs offer advantages for high myopes, including improved best-corrected vision due to less minification of images at the retinal plane, and less aberrations than corneal laser surgery, noted Prof Nuijts, of the Academic Hospital Maastricht, The Netherlands. However, careful patient selection is crucial to minimise complication risks.

LONG-TERM FOLLOW-UP
Adequate endothelial cell density and anterior chamber depth are critical to avoid corneal decompensation, as are sufficient clearance of the iris and crystalline lens to avoid elevated IOP and cataract, Prof Nuijts said. He also recommended avoiding patients who rub their eyes. He also advised long-term follow-up to detect endothelial cell loss or changes in anterior chamber anatomy that threaten endothelial health. According to Dutch Society for Refractive Surgery guidelines, phakic IOLs generally may be implanted in patients 18 years old or older with -2.0 to -23.5 D myopia, +3.0 to +12.0 D hyperopia or 2.0 to 7.0 D astigmatism. Minimum endothelial cell density varies, ranging from 2,800/mm2 for 21-25 year-olds to 2,000/mm2 for patients over age 45.

Contraindications include mesopic pupil diameter >7.0mm, anterior chamber depth <3.2mm including corneal thickness and irregular or abnormal anterior chamber anatomy or iris configuration, such as a forward bulging iris, Prof Nuijts said. He cautioned that anterior segment diameter measurements may vary among instruments. Other safety criteria Prof Nuijts recommends for anterior chamber lenses include >2.8mm distance from the dome of the natural lens to the endothelium (Baumeister. AJO 2004; 723-31); 1.5mm or more from lens edge to endothelium (Baikoff.,JCRS 2006; 1827-35); 2.0mm or more from lens centre to endothelium (Guell, JCRS 2007; 1398-404). Simulating lens placement in an OCT image can help determine if sufficient clearance exits, he noted.

Two iris-fixated IOLs currently available are the Artisan/Verisyse, a non-foldable PMMA lens and the Artiflex/Veriflex, a foldable silicone optic with PMMA haptics, from Ophtec or Abbott Medical Optics. Both offer toric options. Introduced in 1986, the Artisan has proven stable, predictable and safe in several long-term studies, including a 10-year follow up by Prof Nuijts and colleagues (Tahzib et al. Ophthalmol 2007; 1133). In follow-up studies of at least three years, efficacy in achieving at least 20/40 uncorrected ranged from 33 per cent to 95 per cent of patients. Safety is also excellent with loss of two lines best corrected vision rates ranging from 0.0 to 2.6 per cent. Endothelial cell loss ranged from 0.6 to 14.1 per cent annually, he noted.

DEPOSITION
Only one two-year follow-up exists of the Artiflex lens, introduced in 2003, Prof Nuijts said. It showed good predictability, efficacy and safety, with 0.8 per cent losing two lines best corrected, though 4.8 per cent experienced pigment depositions and 1.4 per cent non-pigment depositions (Dick. Ophthalmol 2009; 116). Deposition has also been an issue with the toric Artiflex. A new version using a hydrophobic acrylic optic will go into trials shortly, Prof Nuijts said. Angle-supported anterior chamber lenses fall into two categories, Prof Nuijts said. Early rigid designs led to endothelial cell loss of up to 30 per cent and iris ovalisation in up to 40 per cent of eyes, leading to their removal from the market.

However, a newer angle-supported lens, Cachet from Alcon, has performed much better, Prof Nuijts said. In five studies, between 97.1 per cent and 100 per cent of patients achieved 20/40 or better uncorrected with two line best corrected loss ranging from 0.0 to 0.9 per cent. Endothelial cell loss ranged from 4.0 to 6.2 per cent at one year (see figure below). However, in one three-year follow-up, after an acute loss of 3.3 per cent, chronic endothelial loss came in at 0.41 per cent, or about the physiological rate, suggesting the lens may have better long-term stability (Knorz., JCRS 2011; 37:469).

The Visian ICL from Staar also delivers excellent refractive and safety results, Prof Nuijts said. In three studies of the latest version, ICM V4, including the FDA prospective study, 68 per cent to 95 per cent achieved 20/40 or better uncorrected with 0.0 to 0.8 per cent losing two lines or more at three, four and five years. Endothelial cell loss rates in a few reports up to five years' follow-up appear similar to anterior chamber designs.