LASIK (Laser-Assisted In Situ Keratomileusis) is a widely performed refractive procedure that reshapes the cornea to correct common vision problems. While often sought by those with “bad” vision, eligibility for the surgery is determined not by the severity of the refractive error alone, but by a comprehensive assessment of the entire eye and the patient’s general health. The procedure is highly effective for many, yet a combination of factors, including the precise prescription strength, corneal structure, and overall health status, can make an individual unsuitable for standard LASIK treatment. The determination of whether a patient qualifies requires a detailed consultation and specific diagnostic measurements.
Refractive Error Limits for Eligibility
The numerical prescription limit is often the first criteria considered when assessing a potential LASIK candidate. Refractive errors are measured in diopters (D), and maximum treatable ranges are established to ensure the safety and predictability of the outcome. For nearsightedness, or myopia, the safe upper limit for correction is generally considered to be around -10.00 to -12.00 diopters, though many surgeons prefer to treat up to -8.00D for optimal results.
Correcting farsightedness, or hyperopia, is typically more restricted, with a generally accepted maximum limit of approximately +4.00 to +6.00 diopters. This lower range is due to the nature of the corneal reshaping required for hyperopia, which can be less predictable at higher powers. Astigmatism, which is an uneven curvature of the cornea, can often be corrected up to 5.00 or 6.00 diopters, frequently in combination with myopia or hyperopia.
Exceeding these established diopter limits means that too much corneal tissue would need to be removed to achieve the desired correction. This extensive removal can compromise the structural integrity of the cornea, increasing the risk of complications such as corneal ectasia, a progressive bulging of the cornea. Patients with prescriptions beyond these maximums are usually disqualified from standard LASIK, regardless of their other health factors.
Essential Requirements Beyond Prescription
Beyond the specific prescription strength, a patient must meet several systemic and ocular health requirements to be considered a safe candidate for LASIK. A minimum age of 18 years is required, as visual prescriptions must be stable, ideally showing no significant change for at least one to two years. Surgical results are intended to be permanent, so operating on an eye where the refractive error is still progressing would lead to a poor long-term outcome.
Certain systemic health conditions can also prevent a patient from undergoing the procedure due to their potential to impair the body’s healing process. Uncontrolled autoimmune diseases, such as Lupus or active Rheumatoid Arthritis, are typically absolute contraindications, as they can cause unpredictable healing and increase the risk of post-operative complications. Uncontrolled diabetes can also be a contraindication because it may slow wound healing and increase the eye’s susceptibility to infection.
Hormonal changes can temporarily alter the shape and focusing power of the eye. For this reason, women who are pregnant or nursing are absolutely excluded from LASIK candidacy until several months after they have stopped breastfeeding, to ensure hormone levels and vision are stable. Severe dry eye syndrome is another common disqualifier, as LASIK can temporarily worsen dryness, potentially leading to discomfort and impaired healing.
The Critical Role of Corneal Health
The physical characteristics of the cornea are often the ultimate deciding factor for LASIK eligibility, even if a patient’s prescription falls within the treatable range. The cornea must possess sufficient thickness to safely accommodate the creation of the flap and the subsequent laser reshaping of the underlying tissue. Most surgeons prefer a minimum corneal thickness of at least 500 microns (µm) for a standard LASIK procedure.
During the surgery, a thin flap, typically 90 to 120 µm thick, is created and lifted. Following the laser ablation to correct the vision, a specific amount of tissue must remain in the untouched posterior section of the cornea, known as the residual stromal bed. Experts generally agree that this remaining bed must be at least 250 µm thick to maintain the cornea’s long-term structural integrity and prevent corneal ectasia.
The shape, or topography, of the cornea is also meticulously analyzed to rule out underlying structural weaknesses. Conditions like keratoconus, a progressive disorder where the cornea thins and bulges into a cone shape, are an absolute contraindication for LASIK. Performing LASIK on an eye with an irregular or thin cornea significantly increases the risk of serious post-operative complications and unpredictable vision outcomes.
When LASIK Alternatives Are Needed
For patients who are ineligible for LASIK due to a prescription that is too high, corneas that are too thin, or other disqualifying factors, several effective alternatives exist.
Photorefractive Keratectomy (PRK)
Photorefractive Keratectomy (PRK) is a surface ablation procedure that reshapes the cornea without creating a flap. This makes it suitable for those with thinner corneas or professions with a high risk of eye trauma. While PRK offers similar final visual results to LASIK, the recovery period for the surface layer to heal is longer.
Implantable Collamer Lens (ICL)
Another option is the Implantable Collamer Lens (ICL), which involves surgically placing a biocompatible lens behind the iris and in front of the natural lens. ICLs are particularly beneficial for correcting high prescriptions that exceed LASIK’s limits, as this procedure does not remove any corneal tissue.
Refractive Lens Exchange (RLE)
For older patients, especially those with very high prescriptions or early signs of cataracts, Refractive Lens Exchange (RLE) may be recommended. RLE is similar to cataract surgery, where the natural lens is removed and replaced with an artificial intraocular lens to correct the vision.