Several factors can make you ineligible for LASIK, ranging from the shape and thickness of your corneas to your overall health, your age, and even whether your prescription is still changing. Some of these are permanent disqualifiers, while others are temporary or can be addressed before surgery. Here’s what surgeons evaluate and what might take LASIK off the table.
Corneas That Are Too Thin
LASIK works by reshaping the cornea with a laser, and that means removing tissue. Your cornea needs enough thickness to withstand both the creation of a flap and the reshaping underneath it. Many surgeons consider corneas thinner than 500 microns (about half a millimeter) a concern, though some will operate on thinner corneas with careful planning.
The critical measurement is what’s left afterward: the residual stromal bed. Most surgeons want at least 300 microns of untouched corneal tissue remaining after the procedure to preserve the cornea’s structural strength. Going below that threshold raises the risk of the cornea bulging forward over time, a condition called ectasia that can seriously damage your vision. Another guideline surgeons use is the percentage of total corneal tissue altered. If the flap thickness plus the tissue removed exceeds about 40 percent of the original corneal thickness, the procedure is generally considered too risky.
Keratoconus and Corneal Disease
Keratoconus is a condition where the cornea progressively thins and bulges into a cone shape. It’s one of the most clear-cut disqualifiers for LASIK because the procedure would further weaken an already compromised cornea and accelerate the bulging. Even subtle signs of keratoconus on corneal imaging, sometimes called “forme fruste” keratoconus, can disqualify you.
Other corneal problems that rule out LASIK include corneal scars, corneal dystrophies (a group of inherited conditions that affect corneal clarity), and a condition called epithelial basement membrane dystrophy. Irregular corneal topography, meaning your cornea has an uneven surface that doesn’t follow normal patterns, is a red flag that surgeons screen for carefully during your evaluation.
A Prescription That’s Too High
LASIK can only correct prescriptions within a certain range. The FDA-approved limits for one widely used laser system are:
- Nearsightedness: up to -12.0 diopters
- Farsightedness: up to +6.0 diopters
- Astigmatism: up to 6.0 diopters
Higher prescriptions require more tissue removal, which circles back to the corneal thickness issue. Even if your prescription falls within the approved range, a very high correction combined with thinner-than-average corneas could still disqualify you.
An Unstable Prescription
Your vision prescription needs to be stable before LASIK makes sense. The standard requirement is that your prescription hasn’t changed by more than 0.5 diopters in the year before surgery. If your eyes are still shifting, the correction you get today could be wrong within months.
This is the main reason LASIK has an age floor. The FDA approves most LASIK treatments for people 18 and older, with some specific corrections requiring you to be at least 21. Vision tends to still be changing through the late teens and early twenties, so some surgeons prefer to wait until your mid-twenties to be confident your prescription has settled.
Severe Dry Eye
LASIK temporarily reduces corneal nerve sensitivity and disrupts tear production, so pre-existing dry eye is a significant concern. If you already have dry eyes before surgery, you’re at much higher risk for chronic dryness afterward that may not resolve.
During your evaluation, your surgeon will likely perform a Schirmer test, which measures tear production by placing a small strip of paper inside your lower eyelid. A result below 10 millimeters of wetting is a specific indicator that you’ll experience dry eye problems after LASIK. Other warning signs include rapid tear evaporation, staining on the surface of your eye (visible with special dyes), and reduced corneal sensation. Mild dry eye can often be treated beforehand to make you eligible, but severe or chronic dry eye disease may be a permanent disqualifier for LASIK specifically.
Autoimmune Diseases and Diabetes
LASIK requires your body to heal the corneal flap properly, and certain systemic conditions interfere with that process. The FDA specifically flags autoimmune diseases like lupus and rheumatoid arthritis, immunodeficiency conditions like HIV, and poorly controlled diabetes as reasons to avoid LASIK. These conditions can impair wound healing, increase infection risk, and lead to unpredictable outcomes.
Diabetes is worth particular attention. Well-controlled diabetes doesn’t automatically disqualify you, but uncontrolled blood sugar affects the blood vessels and nerves throughout your body, including in your eyes. Diabetic eye disease, even in its early stages, adds a separate layer of risk that most surgeons won’t take on.
Certain medications can also be a problem independent of the condition they treat. Steroids and retinoic acid (used in some acne and skin treatments) can interfere with corneal healing. You may need to stop these medications before becoming eligible, which isn’t always possible.
Pregnancy and Breastfeeding
Pregnancy and breastfeeding cause hormonal shifts that physically change your corneas. Your cornea has receptors for estrogen, progesterone, and androgens, and the surge of these hormones during pregnancy causes the cornea to thicken (from water retention) and change curvature. These changes mean any LASIK measurements taken during pregnancy or nursing would be unreliable, and the correction could end up wrong once your hormones normalize.
The changes in corneal curvature appear to persist throughout breastfeeding, possibly driven by prolactin. The recommendation is to wait until you’ve completely stopped nursing, your regular menstrual cycle has returned, and your prescription has returned to its pre-pregnancy values. If you become pregnant within one year of having LASIK, there’s also a risk of refractive regression, meaning your correction could partially reverse.
Advanced Glaucoma and Cataracts
Advanced glaucoma disqualifies you from LASIK for two reasons: the suction ring applied to your eye during flap creation temporarily raises eye pressure, which can damage an already compromised optic nerve, and LASIK changes your corneal thickness in ways that make future glaucoma monitoring less accurate.
Cataracts that affect your vision are also a disqualifier. If your lens is already clouding, reshaping the cornea won’t solve the underlying vision problem. Cataract surgery, which replaces your natural lens with an artificial one, can often correct your refractive error at the same time, making LASIK unnecessary.
Large Pupil Size
Pupil size in adults ranges from about 4 to 8 millimeters in the dark. If your pupils dilate significantly larger than the treatment zone of the laser, you may experience halos, glare, and starbursts around lights at night. Modern lasers have larger treatment zones than earlier generations, which has reduced this problem, but very large pupils still raise the risk of nighttime visual disturbances.
Alternatives if You’re Not Eligible
Being disqualified from LASIK doesn’t necessarily mean you can’t have any vision correction surgery. PRK (photorefractive keratectomy) doesn’t create a flap, so it preserves more corneal tissue and is often suitable for people whose corneas are too thin for LASIK. Since no flap is involved, the residual tissue calculation is simpler and more of your cornea retains its structural strength. The tradeoff is a longer, more uncomfortable recovery period.
SMILE is a newer procedure that uses a smaller incision than LASIK and doesn’t create a traditional flap, placing its corneal impact somewhere between LASIK and PRK. For people with very high prescriptions that exceed what any laser procedure can correct, implantable collamer lenses (ICL) are an option. These are essentially permanent contact lenses placed inside the eye, leaving your cornea untouched entirely. Your surgeon can help determine which alternative fits your specific situation based on the reason LASIK wasn’t an option.