For many people with less-than-perfect vision, laser eye surgery is a welcome alternative to wearing glasses or contact lenses. Since it hit the market in 1999, millions of Americans have undergone laser insitu keratomileusis (LASIK), and research shows that most are happy with the results.

But like any medical procedure, LASIK carries risks. Now, a study suggests that many patients experience new vision problems post-surgery—such as dry eyes, double vision, and glare—that they didn’t have before.

To evaluate patient satisfaction with LASIK, researchers at the Food and Drug Administration recruited two groups of patients who were good candidates for the surgery. One included 262 active-duty Navy personnel, and the other included 312 civilian adults.

Both groups were given web-based questionnaires to evaluate vision complaints, before their surgery and again after, at one and three months post-op. The civilian participants completed the questionnaire six months afterward, as well.

Unsurprisingly, patients commonly reported visual symptoms and dissatisfaction with vision before having LASIK. And here’s the good news: The overall prevalence of visual symptoms and dry eye did go down after surgery.

But 43 percent of people in the Naval group, and 46 percent in the civilian group, reported visual symptoms—such as double images, glare, halos, and starbursts—after surgery that they hadn't reported before. And in both groups, about 28 percent of patients who had no significant dry-eye problems before surgery had mild to severe symptoms three months afterward.

“Hence, patients should be adequately informed about the potential risk of developing dry eye symptoms, even if they are asymptomatic preoperatively,” wrote Malvina Eydelman, M.D., an ophthalmologist with the FDA’s Center for Devices and Radiological Health, and her co-authors.

While most participants said they were happy with their results, between 1 and 4 percent of patients reported dissatisfaction with their vision post-LASIK, and 1 to 2 percent reported dissatisfaction with the surgery itself.

Although visual symptoms were common, only a few participants said they caused significant functional limitations. And their prevalence decreased between three and six months post-op—a finding that’s consistent with previous research showing improvement in visual symptoms over time.

The study, published today in JAMA Ophthalmology, is one of the few to report on the development of new visual symptoms after LASIK. Because the results were self-reported, however, the authors can’t say for sure how many symptoms were truly new (and likely caused by the surgery) and how many were a regression to patients’ previous conditions.

What they do know, based on the results of this study compared with previous ones, is that people are more likely to report vision problems post-surgery when given an online survey, as opposed answering questions in person or to talking with a doctor.

“The reluctance of patients to report ‘negative’ events to their health care professional has been documented,” the authors wrote. Allowing people to answer questionnaires in private, with the assurance that their doctor won’t see their responses, has been shown to decrease biased responses, they added.

In this case, the authors estimate that collecting information about symptoms after LASIK in person (a doctor-conducted survey in the office, for example) could be underestimating the rate of problems by a factor of 2 to 4.

The authors say that the questionnaire used in the study—called the Patient-Reported Outcomes With LASIK (PROWL) questionnaire—should be made available online for patients to take before and after surgery. This would be an especially useful tool for gathering data in future clinical trials, they argue.

“A better understanding of the patients' perceptions following this procedure will lead to better outcomes and will provide better information for informed consent to patients considering LASIK surgery,” they wrote.

Of course, biased results are still possible, even with an online survey. “It is possible that participants were more likely reporting satisfaction in an attempt to be consistent with and justify their choice to have surgery,” the authors wrote, “leading to an underestimation of symptom rates and an overestimation of satisfaction rates.

And they note that because of relatively small sample sizes and a limited follow-up period, their findings may not be generalized to all people undergoing LASIK. To better understand which patients are more likely to be dissatisfied with surgery, they say, larger, long-term studies are needed.

 

This article originally appeared on RealSimple.com.