Two vision correction
techniques look comparable
NEW YORK — Two forms of laser vision correction sometimes used as an alternative to LASIK seem to have similar results for people with nearsightedness, a new research analysis finds.
The findings, published in the journal Ophthalmology, confirm results from smaller studies suggesting that patients fare about as well with either of the procedures – namely, photorefractive keratectomy (PRK) and LASEK, a relatively newer technique that differs from its much more common sound-alike LASIK.
Since it was introduced in the US in the 1990s, LASIK has become by far the most commonly used surgical technique for correcting nearsightedness, farsightedness and astigmatism.
But PRK and LASEK are both options for people who cannot undergo LASIK because of certain factors, such as relatively thin corneas.
Like LASIK, the two procedures improve vision by using a laser to reshape the middle layer of the cornea, the transparent membrane that domes over the pupil. The basic difference among the three techniques is that they differ in how the outer layer of the cornea is managed.
With LASIK, the surgeon cuts away a thin "flap" of tissue to gain access to the middle layer of the cornea, and once the surgery is complete the flap is replaced. With PRK, which emerged in the 1980s, there is no flap; instead the top-most layer of the cornea is removed, then naturally regenerates after surgery.
LASEK, which has been in use for about a decade, combines elements of PRK and LASIK. As with the latter, the surgeon makes a flap of corneal tissue, but it’s a thinner one, created using a microsurgical blade and an alcohol solution.
Compared with PRK, people who undergo standard LASIK tend to have less post-operative pain and shorter recovery times: with LASIK, patients often have good vision the next day, whereas with PRK, corneal healing typically takes a few days, and patients may need a week to have clear vision.
So in theory, LASEK could also have an advantage over PRK as far as recovery time and post-operative pain, according to the researchers on the new review, led by Dr. Li-Quan Zhao of Xinhua Hospital in Shanghai, China.
But in an analysis of a dozen studies since 2001, the researchers found that PRK- and LASEK-treated eyes showed no differences as far as vision improvement, postoperative pain or recovery time.
The studies included in the analysis were relatively small – with all 12 involving a total of 542 patients. Ten of the studies were clinical trials in which patients had one eye randomly selected for treatment with PRK and the other with When the researchers combined the studies’ results, they found that both techniques carried a corneal healing time of about three to four days. And patients’ postoperative pain ratings were similar for the PRK- and LASEK-treated eyes.
Vision improvements were similar as well. Across the six studies that reported the proportion of patients who came away with 20/20 vision or better, 197 of 320 PRK-treated eyes showed such an improvement; that compared with 204 of 314 LASEK-treated eyes – a statistically insignificant difference. Most eyes ended up with at least 20/40 vision.
"This study basically confirms what most of us have thought," said Dr. James Salz, a clinical professor of ophthalmology at the University of Southern California, Los Angeles, and a spokesman for the American Academy of Ophthalmology.
When LASEK first came out, Salz noted in an interview, there was a lot of "hype" that it might rival LASIK.
The idea of combining elements of the PRK and LASIK procedures was that it might limit the downsides of the two – such as the longer recovery time with PRK and the heightened risk of dry eyes with LASIK.
Instead, LASEK and PRK appear comparable, Salz said.
The one difference that emerged in the current study was that PRK-treated eyes had a greater risk of "corneal haze" in the first few months after surgery, though not by the sixth month.