LASIK surgery corrects three common vision problems: nearsightedness (myopia), farsightedness (hyperopia), and astigmatism. It can also be used in a modified approach to help with age-related difficulty reading up close. All of these conditions stem from how light bends as it enters the eye, and LASIK fixes them by reshaping the cornea, the clear front surface responsible for most of that bending.
How LASIK Reshapes the Cornea
Your cornea does most of the work of focusing light onto the retina at the back of your eye. When the cornea’s curvature doesn’t match the length of your eyeball, images land slightly in front of or behind the retina instead of directly on it. That mismatch is what makes things look blurry.
During LASIK, a surgeon creates a thin flap on the cornea’s surface, folds it back, then uses a programmed laser to remove tiny amounts of tissue. Each pulse of the laser reshapes the cornea’s curvature so light focuses correctly. The flap is laid back into place and heals without stitches. The entire procedure typically takes under 30 minutes for both eyes.
Nearsightedness (Myopia)
Nearsightedness is the most common reason people get LASIK. If you’re nearsighted, distant objects look blurry because your eyeball is slightly too long or your cornea curves too steeply, causing light to focus in front of the retina. The laser flattens the central cornea so light reaches the retina properly.
People with mild to moderate nearsightedness tend to have the best outcomes. Those with severe myopia can still be candidates, but results become less predictable at higher prescriptions because more tissue needs to be removed. The surgeon must leave enough corneal thickness behind to keep the eye structurally stable, with a minimum residual thickness generally kept above 275 to 300 microns.
Farsightedness (Hyperopia)
Farsightedness is the opposite problem: close objects are blurry because the eyeball is slightly too short or the cornea is too flat. Here the laser removes tissue around the edges of the treatment zone, making the central cornea steeper so it bends light more strongly.
LASIK can treat farsightedness up to about +6.0 diopters. One important limit is that the post-procedure cornea generally shouldn’t exceed a steepness of around 49 to 50 diopters, because going beyond that threshold has traditionally been linked to less predictable visual outcomes. Recent research has questioned whether that cutoff is as rigid as once thought, but surgeons still use it as a practical safety guideline. Overall, farsighted corrections are effective but carry slightly more variability than nearsighted ones.
Astigmatism
Astigmatism means the cornea is shaped more like a football than a basketball, with one axis curving more steeply than the other. This causes blurred or distorted vision at all distances because light splits into two focal points instead of one. The laser selectively removes tissue along the steeper axis, evening out the curvature so it focuses light into a single point.
LASIK can correct astigmatism up to about 5 to 6 diopters, and it’s frequently treated alongside nearsightedness or farsightedness in the same procedure. One important distinction: LASIK treats regular astigmatism, where the two corneal axes are consistently different but symmetrical. Irregular astigmatism, where the corneal surface is unevenly warped, often signals an underlying condition like keratoconus and is a contraindication for the surgery.
Age-Related Reading Difficulty (Presbyopia)
After about age 40, the lens inside your eye gradually loses flexibility, making it harder to focus on close-up text. This is presbyopia, and it’s why many people eventually need reading glasses. LASIK doesn’t restore the lens’s flexibility, but it can work around the problem through a technique called monovision.
With monovision LASIK, one eye (usually the dominant one) is corrected for distance vision and the other is intentionally left slightly nearsighted to handle reading. In one study of patients who had this approach, 89% achieved near reading acuity of 20/40 or better, compared to just 5% before surgery. Candidates typically do a trial with contact lenses or trial frames beforehand to make sure they’re comfortable with the slight imbalance between eyes. The tradeoff is a modest reduction in depth perception and contrast sensitivity, which most people adapt to but some find bothersome.
What LASIK Cannot Correct
LASIK reshapes the cornea, so it only addresses vision problems caused by corneal curvature or eye length. It does not treat conditions inside the eye like cataracts (a clouded lens) or glaucoma (optic nerve damage from elevated eye pressure). It also cannot correct vision loss from retinal diseases such as macular degeneration or diabetic retinopathy.
Certain corneal conditions disqualify someone from LASIK entirely. Keratoconus, a progressive thinning and bulging of the cornea, is the most important one. Removing tissue from an already weakened cornea can cause it to bulge further, a complication called ectasia. Corneal topography mapping during the pre-operative evaluation is specifically designed to catch keratoconus and related conditions, even in their earliest subclinical stages.
Typical Success Rates
LASIK outcomes are well documented. Across large patient populations, 90 to 95% achieve 20/20 vision or better after surgery, and 99.5% reach at least 20/40, the threshold for driving without corrective lenses in most states. People with low to moderate prescriptions consistently land at the higher end of those ranges, while those with very strong prescriptions or combined conditions (high myopia plus significant astigmatism, for example) see more variable results.
Visual quality goes beyond just reading an eye chart. Some patients notice glare or halos around lights at night after surgery, which are related to subtle optical imperfections called higher-order aberrations. Newer wavefront-guided LASIK technology maps these imperfections before surgery and programs the laser to minimize them, which has improved both nighttime vision quality and overall satisfaction compared to earlier techniques.
Who Qualifies
Beyond having a treatable prescription, candidates need a stable prescription that hasn’t changed by more than 0.5 diopters in the past year. Most surgeons require patients to be at least 18, though many prefer to wait until the mid-20s when prescriptions are more likely to have fully stabilized.
Corneal thickness matters because the laser removes tissue to do its work. If your corneas are naturally thin, there may not be enough material to safely reshape them while leaving a structurally sound foundation. The surgeon calculates this in advance, factoring in both the flap thickness and the depth of correction needed. People with adequate thickness, normal corneal topography, and stable prescriptions within the treatable range are generally strong candidates.