You’re tired of eyeglasses and contacts and considering Lasik. Friends who have had the vision-correcting surgery seem pleased with the results—but you’ve noticed that some of them are still wearing glasses. Shouldn’t they not need glasses anymore? Before you decide, here’s what you need to know—and might not get told—about Lasik.

Laser eye surgery, called Lasik, is usually used to correct myopia (nearsightedness), although it can also correct hyperopia (farsightedness) and astigmatism. The surgery has become very popular since it was FDA-approved in the late 1990s. But while Lasik is considered a safe surgery and is often advertised as an easy alternative to glasses and contact lenses, the reality is that it’s more difficult to get a perfect vision correction with Lasik than with glasses or contact lenses…and less predictable.

Myopia occurs because of changes that happen, usually before age 20, to the shape of the eye, the lens or the cornea (the transparent outer layer on the front of the eye). The cornea and the lens (which is behind the cornea) focus light on the retina at the back of the eye, where light-sensitive cells send visual signals to the brain. With myopia, the eye either has become too long or the lens has become too curved, both of which cause the focal point to fall short of the retina. This makes focusing on what is up close easy, while focusing on what is distant is difficult.

YOUR EYES STILL CHANGE

Lasik removes layers of the cornea so that the focal point can reach the retina. These surgical changes to the shape of the cornea are permanent…but the results are not. That’s because the elasticity of the cornea and the shape of the eye can change over time, a condition called myopic regression. In fact, studies show that by 10 years after Lasik, about 70% of people have significant myopic regression and need to wear glasses or contact lenses.

Myopic regression is not the only problem. You may find yourself needing to wear glasses or contact lenses right after the surgery (after you’ve healed and your vision has stabilized), because the correction isn’t as exact as with eyeglasses or contacts. According to a 2013 Consumer Reports National Research Center report, 55% of people still needed to wear glasses or contact lenses at least some of the time after their surgeries.

Lasik surgery also does not prevent presbyopia, the natural loss of elasticity in the cornea that occurs with age and makes it harder to focus on near objects. Presbyopia usually starts after age 40, but laser surgery can cause it to start sooner—so you might need reading glasses sooner, too.

Also, how pleased you’ll be with the results of Lasik depends on what your vision needs are. For example, a garage mechanic handling physical car parts may be fine with less-than-sharp vision—especially if the tradeoff is that eyeglasses are no longer getting in the way. On the other hand, a mechanical engineer who spends his/her day working on detailed computer programs may not be as happy with post-Lasik vision.

KEEPING YOUR EYES HEALTHY AFTER LASIK

Whether or not you have Lasik, myopic regression and presbyopia happen and there is really nothing you can do to slow or prevent either. The good news is that if you do end up needing eyeglasses and/or contacts after Lasik, you may not need to wear them as frequently and you may not need as strong a prescription. If you’re wearing “Coke-bottle bottoms” now, that could definitely be a plus!

Meanwhile, you can still protect your vision from other sight-stealing conditions by keeping your eyes healthy

• Eat plenty of leafy greens, dark berries and other colorful plants. While there is no evidence that they slow myopic regression, the antioxidants have been linked to better overall eye health, including lower risk for macular degeneration.

• Maintain good posture when reading or working on your computer to help prevent eyestrain. Also make sure to have good lighting that illuminates what you are reading without creating glare.

• Aerobic exercise, including walking, running, biking and dancing, can protect against age-related macular degeneration and other retina problems.

• Optometric vision therapy may strengthen and balance the muscles that control eye movement. If you want to try these eye exercises, it’s best to talk to an optometrist rather than try do-it-yourself vision exercises found online or advertised elsewhere. To be effective, these exercises need to be designed and taught by a trained eye specialist.

Bottom line: As long as you don’t go into it “starry eyed,” Lasik may still be a good option for you. Before you decide, have a frank discussion with your vision professional about what to realistically expect.