Implanted Lenses May Treat Milder Nearsightedness
May 12, 2010 — An eye operation typically reserved for patients with severe nearsightedness may be a safer alternative to standard laser eye surgery for patients with less severe forms of nearsightedness, according to a new report published in the recent issue of The Cochrane Library.
Researchers at Moorfields Eye Hospital NHS Foundation Trust in London reviewed three clinical trials that randomly assigned patients to different types of surgery used to correct nearsightedness (myopia).
Myopia is the leading cause of vision impairment around the globe, according to the World Health Organization.In the U.S., 32 million people aged 40 and older are myopic.
The more common surgical procedure, excimer laser refractive surgery, treats myopia by removing parts of the cornea. The second procedure, which is relatively new and not used as widely, implants a thin lens called a phakic intraocular lens (IOL) permanently into the eye to eliminate the need for eyeglasses or contact lenses. Both procedures change the path of light entering the eye and bring images into sharper focus. Phakic IOLs were approved by the FDA in 2004.
Phakic IOLs: Risk of Cataracts
The study showed that one year after undergoing the procedure, 20/20 vision without eyeglasses was the same for patients who received either laser surgery or phakic IOLs. One year after the surgical procedure, the phakic IOL patients had clearer spectacle-corrected vision, better contrast sensitivity (the ability to perceive differences between an object and its background), and higher satisfaction scores than laser eye surgery patients. However, there was a slight increased risk of developing cataracts among the phakic IOL group.
The researchers’ conclusions were based on three clinical trials that included a total of 228 eyes in 132 men and women ranging in age from 21 to 60. The patients had moderate to severe myopia.
The advantages of phakic IOLs are that “it does not involve removing any corneal tissue, and it is reversible. … In the unlikely event of any problems the synthetic lens can be removed at a later date,” study author Allon Barsam tells WebMD in an email interview.
“Our findings suggest phakic IOLs are safer than excimer laser surgery” for correcting moderate to high levels of nearsightedness, Barsam says. “Although it’s not currently standard clinical practice, it could be worth considering phakic IOL treatment over the more common laser surgery” for patients with moderate nearsightedness.
Regarding the risk of cataracts, Barsam says more long-term studies are needed to assess any risks that might not arise during a one-year follow up and that might be unique to phakic IOL patients.
James Salz, MD, clinical professor of ophthalmology at the University of Southern California at Los Angeles and a spokesman for the American Academy of Ophthalmology, says the data reviewed in this report are too limited to draw any immediate conclusions that would change current practices.
“It’s a bit misleading with a small review like that because it’s just a few hundred cases,” Salz tells WebMD. “Most of us would not agree it’s safer to do an intraocular lens procedure because it’s a more invasive procedure. Laser surgery doesn’t cause cataracts in anybody, but phakic IOLs cause cataracts in a percentage of people. I don’t think that study would change the opinion of most surgeons who would do this surgery on a daily basis.”
Salz says phakic IOLs might be an option for moderate myopia in patients with abnormal-shaped corneas, but he says “those cases are rare.”
D. Rex Hamilton, MD, director of the Laser Refractive Center at the Jules Stein Eye Institute at the University of California at Los Angeles, says the findings in this review reflect his own clinical experiences.
“The findings of this study are consistent with my clinical experience that LASIK is extremely safe and effective up to moderate levels of myopia (-7 to -8 D),” Hamilton tells WebMD in an email interview. “Above this range, LASIK patients tend to lose some contrast sensitivity (the ability to see shades of grey) particularly in dim light settings. Phakic IOLs have an advantage with regard to contrast sensitivity in the highly myopic population. Although there is a slightly increased risk of cataract formation with phakic IOL implantation (particularly in higher corrections, above -15 D and in patients over the age of 40 at the time of implantation), phakic IOL implantation remains the procedure of choice for highly myopic patients who qualify.”