LASIK isn’t safe or effective for everyone. Roughly 15 to 20 percent of people who inquire about the procedure learn they’re not good candidates, typically because of corneal shape, prescription instability, dry eyes, or underlying health conditions. Some of these disqualifiers are permanent, while others are temporary, meaning you may become eligible later.
Unstable or Extreme Prescriptions
Your eyeglass prescription must have been stable for at least two consecutive years before LASIK is considered. If your vision is still shifting, reshaping the cornea now could leave you with blurry vision again within months. This is the main reason younger adults are often told to wait: the FDA approves LASIK for ages 18 and up, but many surgeons recommend holding off until your mid-20s, when prescriptions tend to settle.
There are also upper limits on how much correction LASIK can deliver. Very high degrees of nearsightedness, farsightedness, or astigmatism require removing or reshaping more corneal tissue than is safely possible. For farsightedness specifically, surgeons generally avoid steepening the cornea beyond about 49 to 50 diopters after surgery, which limits how much hyperopia can be treated. If your prescription falls outside the treatable range, alternatives like implantable lenses are typically a better fit.
Thin or Irregularly Shaped Corneas
LASIK works by creating a thin flap in the cornea and then using a laser to reshape the tissue underneath. That process removes corneal material, so you need enough thickness to start with. Many surgeons look for a starting corneal thickness above 500 microns (about half a millimeter), though the more important number is what’s left afterward. The FDA suggests maintaining at least 250 microns of remaining tissue beneath the flap, and most surgeons aim for 275 to 300 microns to build in a safety margin.
When too much tissue is removed relative to what’s available, the cornea can gradually bulge forward in a condition called ectasia, causing progressive vision distortion similar to keratoconus. In fact, preexisting keratoconus, even in its earliest subclinical stages, is one of the biggest risk factors for this complication. A 2014 analysis found that removing a high percentage of corneal tissue (40 percent or more of total thickness) carried a dramatically elevated risk of post-surgical ectasia. Surgeons now screen carefully with corneal mapping to catch any irregularity before clearing someone for the procedure.
Severe Dry Eye Disease
LASIK temporarily worsens dry eye in almost everyone because creating the corneal flap cuts some of the nerves that signal your eye to produce tears. For most people, this resolves within a few months. But if you already have significant dry eye before surgery, the procedure can push symptoms into chronic territory.
During screening, your surgeon will measure tear production. One common test involves placing a small strip of paper under your lower eyelid for five minutes. Wetting below 5 millimeters generally signals probable dry eye, and results at or near zero are a clear disqualifier. Symptoms like persistent grittiness, burning, or visible corneal surface damage on examination also raise red flags. Mild dry eye can sometimes be treated first, making LASIK possible later, but severe or chronic cases often point toward a different procedure entirely.
Autoimmune Conditions and Diabetes
The FDA specifically flags autoimmune diseases like lupus and rheumatoid arthritis, immunodeficiency conditions like HIV, and diabetes as factors that may prevent proper healing after LASIK. These conditions affect how your body manages inflammation and repairs tissue, both of which are critical in the weeks after corneal surgery. Uncontrolled diabetes is particularly concerning because it can cause unpredictable changes in your lens and vision independent of the cornea itself.
If you have one of these conditions but it’s well managed, some surgeons will still consider you on a case-by-case basis. The key distinction is between a condition that’s stable and under control versus one that’s active or poorly regulated.
Medications That Impair Healing
Certain medications interfere with how the cornea heals after surgery. The FDA highlights two categories in particular: retinoic acid (commonly used in prescription acne treatments like isotretinoin) and steroids. Retinoic acid can thin the cornea and impair wound healing. Long-term steroid use suppresses the immune response your eye needs to recover. Immunosuppressant drugs carry similar concerns. If you’re currently taking any of these, your surgeon will likely ask you to stop well in advance or may recommend against LASIK altogether.
Pregnancy and Nursing
Hormonal fluctuations during pregnancy and breastfeeding can temporarily change the shape of your cornea and shift your prescription. Your eye pressure also changes during this period. Because LASIK depends on precise, stable measurements, surgery during pregnancy or while nursing could produce inaccurate results. Most doctors recommend waiting three to six months after you finish breastfeeding before even scheduling a LASIK evaluation. This gives your hormones time to level off and your vision time to return to its baseline.
Large Pupils
If your pupils dilate unusually wide in dim light, you face a higher risk of visual disturbances after LASIK. When the pupil opens beyond the zone that was reshaped by the laser, light entering the untreated area scatters, producing halos, glare, and starbursts around lights at night. Research has confirmed a significant correlation between large pupil size measured before surgery and worsened night vision afterward. Modern lasers treat wider zones than earlier generations, which has reduced this problem, but very large pupils remain a concern your surgeon should measure and discuss.
Alternatives if You’re Not a Candidate
Being told no to LASIK doesn’t mean you’re out of options. The right alternative depends on why you were disqualified.
- PRK (photorefractive keratectomy) is the most common alternative for people with thin corneas. It skips the corneal flap entirely, instead reshaping the surface directly after removing the outer cell layer. This preserves more tissue and lowers the risk of ectasia, though recovery takes longer since that outer layer needs to regrow.
- Implantable collamer lenses (ICL) work well for high prescriptions or thin corneas. A small lens is placed inside the eye between the iris and your natural lens, similar to a permanent contact lens. No corneal tissue is removed, and the procedure is reversible.
- Refractive lens exchange replaces your natural lens with an artificial one, similar to cataract surgery. It’s best suited for people over 40, especially those already developing age-related focusing difficulty, and it doesn’t depend on corneal thickness at all.
- Orthokeratology uses specially designed rigid contact lenses worn overnight to temporarily reshape the cornea while you sleep. It’s completely reversible and works for people with thin corneas, dry eyes, or those too young for surgery, though it can’t correct high prescriptions.
A thorough screening appointment will identify exactly which factors affect your candidacy. Many of the conditions that rule out LASIK, like dry eye, unstable prescriptions, or pregnancy, are temporary. Others, like thin corneas or keratoconus, simply redirect you toward a procedure that’s designed for your specific situation.