Ads from LASIK surgery outfits promise that the procedure is “a permanent solution for vision correction.” “Make corrective eyewear a thing of the past.” “You might never need to drop another dollar on eye care at all.” The procedure is “painless.” “More than 99 percent of LASIK patients achieve 20/20 vision or better.” And “over 98 percent of patients are totally satisfied.”

Unfortunately, those claims stretch the truth.

You Likely Will Still Need Glasses

For starters, LASIK vision fixes are usually only temporary. If you want to be forever free of corrective lenses—the leading reason consumers opt for LASIK—you may be disappointed.

Most of the underlying problems that LASIK is used to treat involve the inability of your eyes to focus sharply on objects far away (nearsightedness, or myopia) or up close (farsightedness, or hyperopia). Another one is astigmatism, which is visual distortion or blurriness caused when a football-shaped cornea contorts the images it casts onto a basketball-shaped retina.

All three of these problems result from structural imperfections in the eyeball, which cause light entering the window of the cornea and streaming through the lens to be imprecisely focused on the retina, preventing it from transmitting picture-perfect info to your brain.

LASIK can reshape your cornea to address one type of vision problem—corneal irregularities—but it cannot stop an unrelated and different gremlin: the normal progression of aging that will relentlessly erode any gains made by the surgery.

Your eyes change over time all through your life. Nearsightedness, the most common condition, tends to start in childhood or adolescence and worsens as kids and their eyes grow to adulthood. Usually, nearsightedness actually stops progressing—and vision stabilizes—in one’s early twenties.

But as you continue to age, new vision problems come into play. Your eye’s lenses, which begin life clear, gradually become more yellow, then more brown. That color shift changes the way light gets bent and focused by the lens, and “your prescription will change as the lens changes,” says Rachel Bishop, M.D., chief of the Consult Services Section of the National Eye Institute.

In your forties yet another condition—presbyopia—gradually starts affecting all eyes: No one escapes this. Your lens, pliable in youth, hardens with age, and the muscles that hold the lens in place weaken. Those muscles pull a young, flexible lens taut, or they let the lens relax and contract, so you can almost instantly refocus from far to close-up and back again.

Consequently, the harder, older lens and weaker muscles make it increasingly difficult for you to focus on things up close. Standard LASIK doesn’t treat these hard lenses or weak muscles. “Monovision LASIK” can be a workaround: It corrects one eye to focus sharply at distance and one eye to focus sharply up close, but some patients can’t tolerate that type of change. Beyond that, the only solution to presbyopia is to wear corrective lenses.

Some LASIK patients may not mind an age-related return to eyeglasses or contacts, but “too often, this is overlooked and, particularly for myopes [the nearsighted] who did not need spectacle correction for near work, the need to wear reading glasses can come as a very unpleasant shock,” says Stephen Updegraff, M.D., who has performed tens of thousands of LASIK procedures.

So deterioration in your eyes never stops, whether you wear eyeglasses or get LASIK. But it’s far easier to change up glasses or contacts as your vision changes, or add reading glasses or bifocals, than it is to undergo additional LASIK surgeries—which might not even be an option, if prior laser surgery has removed too much tissue from the cornea.

It’s Surgery, So There Are Risks

Although the chances of having serious complications from LASIK are very low, there are still risks.

LASIK weakens the eye and makes it more vulnerable to injury from the kind of impact common in contact sports, at least for the first year after surgery; if that’s why you got this procedure, you should wear protective goggles when playing ball or hockey.

More common adverse events from LASIK, experienced by fewer than one percent to as many as 49 percent of patients, depending on the problem, are dry or scratchy eyes; discomfort or pain; difficulty driving at night arising from glare, halos, or starbursts around streetlamps, oncoming headlights, and other lights; fluctuations in the sharpness of vision; sensitivity to light; hazy or blurry vision; a feeling of something in an eye; and contrast sensitivity, a reduced sharpness of the defining lines between gray and grayer or colored and lighter-colored things in the field of vision, often encountered while driving at dusk or in rain or fog.

“For most, [these problems] are transient and resolve the first few hours, days, weeks, or months after surgery. Very few patients consider them a long-term problem,” says Sidney Gicheru, M.D., clinical spokesman for the American Academy of Ophthalmology (AAO), whose members include LASIK surgeons.

But many clinical studies of adverse events and complications from LASIK tend not to look for problems beyond the first six to 12 months after surgery. One 2016 study of patients five years after LASIK by Steven Schallhorn, M.D., and six other researchers found that 48 percent still suffered dry eyes, 21 percent endured painful or sore eyes, 31 percent had gritty eyes, and 40 percent remained sensitive to light. Most experienced these problems only occasionally, but two to eight percent endured them half, most, or all the time.

On top of that, six to 19 percent had noticed glare, halos, double images, or ghost images in the previous four weeks. Most of these patients said these issues were only a little bothersome or not at all, while one to three percent said they were somewhat to extremely bothersome.

Last June The New York Times published a damning article about these problems—including some horrific anecdotes—and suggested that the LASIK industry does not sufficiently inform prospective patients of these risks. “The article was correct in many ways,” Gicheru told Checkbook. “As LASIK surgeons, we must do a better job of informing our patients about the risks of surgery. No surgery is risk-free.”

LASIK Isn’t Perfect

Although most LASIK patients are satisfied with their results, there are still plenty who wish they hadn’t done it.

LASIK surgeons often cite a study by Kerry Solomon, M.D., and nine other researchers that found 95 percent of patients are satisfied. But that astronomical level of success is overstated. That 2009 study, sponsored in part by the American Society of Cataract and Refractive Surgery Foundation, looked at 19 survey-based studies of laser eye surgery patients from around the world, and its authors counted patients as satisfied if they indicated they were everything from “somewhat satisfied” to “very satisfied.” Solomon and two of the other researchers are also consultants to the manufacturers of surgical lasers and others in the optical industry.

A more granular 2016 study of satisfaction by Malvina Eydelman, M.D., and several other researchers looked at patient satisfaction with vision after LASIK among patients in the federal government Food and Drug Administration PROWL (Patient-Reported Outcomes With LASIK) studies, based on the varying levels of results they achieved.

Patients’ satisfaction with their post-LASIK vision was assessed in different ways, and those whose vision after LASIK was 20/40 or better or who didn’t need glasses had high satisfaction scores of 88 to 93, on a 0-to-100 scale.

By contrast, the five percent of patients who still needed corrective lenses after LASIK had statistically significantly lower scores of 73 to 81. And the less than 1.7 percent of patients who achieved vision of worse than 20/40  had statistically significantly lower satisfaction scores of 57 to 60.

Meanwhile, the Schallhorn study mentioned above also found 91 percent overall satisfaction five years after LASIK. But only 64 percent were “very satisfied,” while 27 percent were more tepidly “satisfied.”

One reason patients might have high expectations for perfect vision after LASIK is that “we as an industry have set them high [with] buzzwords like ‘high-definition vision’ or ‘20/perfect,’” says Updegraff, who helped pioneer this surgery in 1996.

But 20/40 or better—not 20/20—is not necessarily bad. “If your vision is so poor that you can’t read any lines on the eye chart and LASIK gets you to 20/40, you’ll probably consider that a very good result. But if you were 20/60 and LASIK gets you to 20/40, you probably won’t be happy with that,” says Bishop.

We analyzed data from the manufacturers’ clinical trials for the 33 lasers approved by the FDA since 1998. Among the trials demonstrating effectiveness for nearsightedness, only 69 percent of patients achieved 20/20 or better, on average. Among trials demonstrating effectiveness for farsightedness, only 54 percent of patients achieved 20/20 or better.

There’s more: After LASIK, your vision has a high chance of getting worse because of what doctors call “regression,” the tendency of an eye to return to its original poor vision after surgery. A 2015 South Korean study by Choon-Ki Joo, M.D., and four other researchers, found that 10 years after surgery the nearsightedness of 77 percent of patients treated with LASIK, and 73 percent treated with LASEK had regressed, on average, by about 1.1 to 1.3 diopters.

Diopters measure how much of the light entering an eye is improperly bent and thus out-of-focus. Perfect 20/20 vision translates to 0 diopters, while 20/50 equals -1 diopter. So, if LASIK brought your vision to about 20/50, a -1 diopter regression over 10 years would leave you with 20/125 vision. That is considered “moderate vision loss” by the International Council of Ophthalmology.

In a large 2013 Vision Council survey of 5,056 consumers who had had LASIK less than a year to five or more years prior to the survey, 54 percent reported they had some vision problem that impairs their sight.

Almost 50 percent used some kind of prescription eyeglasses, contact lenses, sunglasses, or readers for near- or farsightedness or presbyopia. The remaining four percent were “squinters,” industry lingo for folks who don’t use any form of corrective lenses, even though they readily admit that they have a vision problem that impairs their sight.

In 2013 Consumer Reports conducted a similar but smaller nationally representative survey of 793 adults who had had LASIK surgery in the previous eight years. Fifty-five percent still needed to wear glasses or contact lenses at least some of the time after the surgery; within that group, 61 percent said they were disappointed about that.

Finally, some LASIK patients—six to 10 percent—may need corrective lenses after surgery due to having too much or not enough corneal tissue removed, so-called overcorrection or undercorrection. If not enough tissue was removed, a second LASIK surgery can “touch up” and remove more tissue to improve visual acuity without glasses. But if too much tissue had been removed, since it can’t be added back, PRK retreatment or eyeglasses or contacts may be necessary.