Vision correction has come a long way since the original hard contact lenses that gained popularity 40 years ago. Phakic intraocular lenses are the equivalent of permanent contact lenses, although the manufacturers do not use the term “contact”. These lenses are surgically implanted in the eye. They are similar to the lenses used to replace the natural lens in cataract surgery, but the natural lens is left in place when a phakic lens is implanted.
Phakic lenses are an alternative to LASIK surgery (laser in situ keratomileusis) for patients who are highly nearsighted. LASIK surgery works well for patients who need relatively small corrections to the refractive power of the cornea, which provides about two thirds of the total light refraction in the eye. By removing part of its tissue, LASIK reshapes the cornea and changes the focal length. But the cornea is very thin. There's a limited amount of material that can be removed. For highly nearsighted eyes, the best corrected visual acuity that LASIK can provide may not be acceptable to the patient. In addition, removing relatively large amounts of corneal tissue may increase the potential for night glare and corneal ectasia, which is an abnormal curvature that interferes with vision.
There are several categories of phakic intraocular lenses:
1. Angle-supported anterior chamber lenses. I have not found any of these commercially available.
2. Posterior chamber lenses. According to Reference 2, there are five lens designs available and almost 35,000 implants completed.
3. Iris-fixated lenses. According to Reference 1, this is the most promising type. The Artisan Phakic IOL was approved by the FDA in 2004. Reference 3 reports that 150,000 have already been implanted.
Reference 1 reports a five-year study of the Artisan Phakic Lens in 26 eyes from 15 patients. The authors conclude that implantation of this lens is effective and generally safe. However, loss of endothelial cells was significant enough for the authors to note: “We recommend caution in contemplating implantation of these phakic IOLs in young patients or those with compromised endothelial cell counts”.
Currently there are four clinical trials underway for phakic intraocular lenses (http://clinicaltrials.gov). Check with your eye doctor for the latest results.
References:
1. Silva RA et al, “Prospective long-term evaluation of the efficacy, safety, and stability of the phakic intraocular lens for high myopia”, Arch Ophthalmol. 2008 June; 126(6): 775-81.
2. Visian ICL lens:
http://www.medcompare.com/details/34728/Visian-ICL.html
3. Verisyse Artisan Phakic Lens:
http://www.medcompare.com/details/34727/Verisyse-ARTISAN-Phakic-IOL.html
4. Complications of LASIK:
http://www.lasikcomplications.com/ectasia.htm
Linda Fugate is a scientist and writer in Austin, Texas. She has a Ph.D. in Physics and an M.S. in Macromolecular Science and Engineering. Her background includes academic and industrial research in materials science. She currently writes song lyrics and health articles.