LASIK, or Laser-Assisted In Situ Keratomileusis, is a popular procedure that reshapes the cornea to correct common refractive errors like nearsightedness, farsightedness, and astigmatism. This surgery can significantly reduce or eliminate the need for glasses or contact lenses, offering visual freedom to millions. However, to maximize the chances of a successful outcome and ensure patient safety, eye surgeons adhere to a strict set of eligibility guidelines. These criteria are not arbitrary exclusions but are based on the physical structure of the eye, the stability of the patient’s vision, and their overall health.
Contraindications Related to Eye Anatomy
The physical characteristics of the cornea, the clear front surface of the eye, are the most frequent reason a patient may not qualify for LASIK. The procedure involves creating a thin flap and then using a laser to remove underlying corneal tissue. If the cornea is naturally too thin, removing the necessary tissue compromises the eye’s structural integrity, potentially leading to a complication called ectasia, where the cornea bulges outward.
Specific corneal shape irregularities are absolute contraindications, particularly diagnosed or suspected keratoconus. This condition causes the cornea to progressively thin and assume a cone-like shape, and the tissue removal involved in LASIK can accelerate this deterioration. Even milder forms of irregular corneal shape, detected through advanced topographic mapping, can make LASIK unsafe.
Furthermore, the presence of certain existing ocular diseases can disqualify a patient. Uncontrolled glaucoma, which involves elevated intraocular pressure, can be complicated by the procedure, which temporarily increases pressure on the eye. Severe pre-existing dry eye syndrome is another concern, as the creation of the corneal flap can temporarily disrupt corneal nerves and worsen tear production, leading to discomfort and impaired healing. Active eye infections or inflammation, such as conjunctivitis, must be completely resolved before surgery.
Vision Stability and Refractive Limits
A patient’s vision prescription must demonstrate a history of stability to ensure the results of the surgery are long-lasting. Surgeons typically require that the refractive error has not changed significantly for at least one to two years prior to the procedure. If a patient’s prescription is still fluctuating, the underlying cause needs to be identified, and the surgery must be postponed until the vision stabilizes.
This requirement for stability is also why a minimum age is enforced, typically 18 years old, although many surgeons prefer to wait until the early to mid-twenties. Younger individuals are more likely to experience natural changes in their eye growth and refraction. Performing the surgery before the vision is stable would mean the corrected result would soon become inaccurate as the eye continues to change.
There are also physical limits to the degree of correction that can be safely performed. If a patient’s nearsightedness, farsightedness, or astigmatism is too severe, correcting it would require removing an excessive amount of corneal tissue. Correction for myopia often has an upper boundary around -10.0 diopters, and hyperopia around +5.0 diopters. Attempting to correct prescriptions beyond these levels increases the risk of complications and unpredictable outcomes.
Systemic Health and Healing Concerns
Overall body health plays a significant role in determining LASIK candidacy because the body’s ability to heal is paramount to a successful recovery. Conditions that compromise the immune system or the body’s wound-healing process are often considered contraindications. Autoimmune diseases like systemic lupus erythematosus or rheumatoid arthritis can impair corneal healing and increase the risk of post-operative complications, particularly severe dry eye.
Uncontrolled diabetes presents a risk due to its potential to impair the body’s ability to heal and increase the likelihood of infection. Patients with diabetes must have their blood sugar levels well-managed before a surgeon will consider proceeding with LASIK. Certain medications, such as immunosuppressants or isotretinoin, can also interfere with the normal wound healing process, necessitating a temporary or permanent deferral of the procedure.
Temporary hormonal fluctuations, such as those experienced during pregnancy and breastfeeding, can cause changes in corneal shape and tear production. Surgeons advise waiting until hormones have stabilized, typically a few months after weaning, to ensure the most accurate and stable surgical result.
Options for Non-Qualifying Patients
For individuals who do not qualify for LASIK due to thin corneas, high prescriptions, or other anatomical issues, several effective alternative surgical options exist. Photorefractive Keratectomy (PRK) is often recommended for patients with corneas that are too thin for LASIK. PRK involves reshaping the surface of the cornea without creating a flap, which preserves more of the underlying structural tissue. While effective, PRK requires a longer recovery period than LASIK.
Small Incision Lenticule Extraction (SMILE)
Small Incision Lenticule Extraction (SMILE) is another flapless procedure that may be an option for certain levels of nearsightedness. This technique uses a laser to create a small, lens-shaped piece of tissue within the cornea, which is then removed through a tiny incision.
Implantable Collamer Lenses (ICLs)
For those with very high prescriptions or severe dry eye, Implantable Collamer Lenses (ICLs), or Phakic IOLs, offer a solution. These are biocompatible lenses surgically placed inside the eye in front of the natural lens, correcting vision without permanently altering the cornea’s shape.