LASIK (Laser-Assisted In Situ Keratomileusis) is an elective surgical procedure designed to correct common refractive errors in the eye. It uses a laser to precisely reshape the cornea, the clear front surface of the eye, improving how light focuses onto the retina. This correction aims to reduce or eliminate the need for glasses or contact lenses for people with nearsightedness, farsightedness, or astigmatism. While highly effective, LASIK is not suitable for everyone, as candidacy depends on meeting strict ocular and systemic health criteria.
Foundational Eligibility: Age and Vision Stability
A foundational requirement for LASIK candidacy is reaching the minimum age of 18 years, set by the U.S. Food and Drug Administration (FDA). This requirement exists because the eye, particularly the cornea, is still developing, and vision prescriptions often continue to change. Although 18 is the minimum, many surgeons prefer to wait until a patient is in their early to mid-twenties, when ocular maturity is more assured.
The stability of your vision prescription is arguably the most important foundational factor, and it must have remained consistent for at least 12 months before surgery. Stability is generally defined as a change of no more than 0.50 diopters in the prescription over the course of a year. If the refractive error continues to progress, the corrective effects of the procedure would be temporary. Hormonal fluctuations, such as those experienced during pregnancy, can also temporarily affect vision stability, which is why the procedure is contraindicated during those times.
Refractive Error Limitations
LASIK corrects refractive errors, which are measured in diopters (D). The procedure’s safety and predictability are tied to the amount of corneal tissue that must be removed to achieve the correction. Consequently, there are established upper limits to the prescriptions LASIK can effectively treat.
For nearsightedness (myopia), the procedure can typically correct prescriptions up to -12.00 D, though many clinics maintain more conservative limits. Farsightedness (hyperopia) is treatable up to approximately +4.00 D to +6.00 D. Astigmatism, an irregular curvature of the cornea, can generally be corrected up to 6.00 D.
If a patient’s prescription falls outside these ranges, the required laser ablation may remove too much corneal tissue, significantly increasing the risk of complications. A prescription that is too high, especially for myopia, would require deep reshaping, potentially compromising structural integrity. In these cases, alternative vision correction procedures, such as Photorefractive Keratectomy (PRK) or implantable lenses, may be recommended as safer options.
Critical Ocular Health Requirements
The physical condition of the eye itself is a major determinant of eligibility, with corneal thickness being a primary concern. The average healthy cornea measures approximately 540 to 560 micrometers (µm) centrally. During LASIK, a thin hinged flap is created, and the underlying tissue is reshaped.
After the procedure, a sufficient amount of corneal tissue, known as the residual stromal bed, must remain to ensure the eye’s structural stability. Most surgeons require this remaining bed to be at least 250 µm to 300 µm to prevent a serious complication called ectasia, where the cornea bulges outward and distorts vision. Patients with naturally thin corneas or those with a high prescription requiring extensive tissue removal may not meet this safety threshold.
Another important factor is the presence of existing chronic dry eye, which can worsen after LASIK. The procedure temporarily disrupts the nerves in the cornea that stimulate tear production, and pre-existing severe dryness can lead to post-operative discomfort and poor healing. Patients with active eye infections, uncontrolled glaucoma, or corneal conditions like keratoconus are also not candidates. Pupil size is also evaluated, as naturally large pupils may experience glare, halos, and starbursts after surgery, especially in low-light conditions.
Systemic and Situational Contraindications
Certain health conditions or temporary life stages can prevent a person from having LASIK. Pregnancy and nursing are temporary contraindications because hormonal fluctuations can lead to temporary changes in vision and corneal shape. Furthermore, medications used during the recovery period may not be safe for a developing baby or a nursing infant.
Systemic diseases that impair the body’s ability to heal are also a concern, as proper wound healing is necessary for a successful outcome. Uncontrolled autoimmune disorders, such as lupus or rheumatoid arthritis, can increase the risk of delayed or incomplete healing and post-operative complications. Immunodeficiency disorders, like HIV, are also considered, as they may compromise the body’s ability to fight off potential infection. Specific eye diseases, including severe cataracts or retinal diseases like diabetic retinopathy, also disqualify a candidate because LASIK would not address the underlying vision problem.