Laser-Assisted in Situ Keratomileusis, or LASIK, is a refractive surgical procedure that corrects common vision problems like nearsightedness, farsightedness, and astigmatism. The procedure uses a laser to precisely reshape the cornea, the clear, dome-shaped front surface of the eye, to improve how light is focused onto the retina. Although the prospect of freedom from glasses and contact lenses is appealing, not everyone who desires the surgery is a suitable candidate. A thorough candidacy screening process is mandatory, ensuring the procedure is safe and likely to yield the best long-term visual outcomes. This evaluation identifies any underlying conditions that could interfere with the healing process or the final result.
Fundamental Eligibility Criteria
The initial consideration for LASIK candidacy is based on age and prescription stability. The U.S. Food and Drug Administration (FDA) has approved the laser technology for individuals who are at least 18 years old. This age requirement is necessary because the eye continues to develop throughout adolescence and early adulthood. Many surgeons prefer patients to be closer to 25 years old, when vision is more likely to have fully stabilized.
A stable vision prescription is required, meaning the refractive error has not changed significantly for at least 12 months. A significant change is defined as a shift of more than 0.5 diopter within that year. If the prescription is still changing, LASIK would be ineffective because the vision correction would not be permanent. Candidates must also possess realistic expectations and understand that while vision is significantly improved, it may not eliminate the need for reading glasses later in life due to presbyopia.
Ocular Requirements and Limitations
Beyond basic eligibility, the physical structure and health of the eye determine technical suitability for the procedure. Corneal thickness is measured using pachymetry, which is important because LASIK involves the permanent removal of corneal tissue. The average cornea measures between 540 and 550 microns thick. During the procedure, a corneal flap is created, typically consuming 90 to 150 microns of tissue, and the excimer laser removes additional tissue based on the required correction.
A safety threshold mandates that a minimum of 250 microns of corneal tissue must remain in the stromal bed after surgery to maintain the cornea’s structural integrity. Many surgeons prefer to leave 300 microns or more to reduce the risk of corneal ectasia, a rare complication where the cornea bulges outward, distorting vision. This thickness limitation often disqualifies individuals with very high prescriptions, such as high myopia, as too much tissue would need to be removed.
Another limitation is the presence of severe chronic dry eye disease. LASIK temporarily disrupts the corneal nerves and can worsen existing dry eye symptoms. Patients with pre-existing severe dry eye are often better suited for alternative procedures like Photorefractive Keratectomy (PRK). Finally, individuals who have very large pupils, especially in dim lighting conditions, may experience glare, halos, or starbursts after surgery, which can be debilitating at night.
Medical Conditions That Prevent LASIK
A patient’s overall health status determines suitability for LASIK because systemic diseases can compromise the body’s healing response. Autoimmune diseases, such as lupus, severe rheumatoid arthritis, or Sjögren’s syndrome, are often contraindications. They interfere with the eye’s ability to heal properly after the surgical incision, increasing the risk of poor outcomes and complications.
Uncontrolled diabetes also poses a risk, as high blood sugar levels can lead to vision fluctuations and delay wound healing. While well-controlled diabetes may not be an absolute contraindication, the presence of diabetic retinopathy or other related eye complications typically disqualifies a candidate. Certain medications can also negatively affect candidacy; for instance, systemic steroids and drugs like isotretinoin, used for acne, impair wound healing and are generally prohibited before and after surgery.
Temporary physiological states, most notably pregnancy and nursing, also serve as contraindications. Hormonal changes during these periods cause vision to fluctuate, making it impossible to obtain an accurate and stable pre-operative prescription. Candidates must wait until several months after they have finished nursing to proceed, as certain post-operative medications may be contraindicated while breastfeeding.