Laser eye surgery, including procedures like LASIK and PRK, corrects common vision issues like nearsightedness, farsightedness, and astigmatism. These procedures reshape the cornea to adjust how light focuses onto the retina. While successful for millions, laser eye surgery is not suitable for everyone seeking permanent vision correction. A comprehensive eye health evaluation is necessary to determine if a patient meets the safety criteria for a predictable outcome. This screening identifies physical and medical factors that could increase the risk of complications or lead to unsatisfactory vision correction.
Eye Characteristics That Prevent Surgery
The cornea’s physical structure is the primary determinant of candidacy because the laser directly modifies this tissue. Insufficient corneal thickness is a common reason for disqualification from LASIK. The procedure requires leaving a minimum amount of untouched tissue, known as the residual stromal bed (typically 250 to 300 micrometers), to maintain the cornea’s structural stability. The original corneal thickness must be sufficient to accommodate the creation of the corneal flap and the tissue removed by the laser.
Patients with high prescriptions often require the removal of too much tissue, leading to upper limits for treatment. For nearsightedness (myopia), the limit is often set around -9.00 to -12.00 diopters, and farsightedness (hyperopia) is typically limited to +6.00 diopters. A higher prescription requires ablating a greater volume of tissue, which impacts the remaining stromal bed and increases the risk of the cornea weakening post-surgery.
Certain pre-existing eye conditions pose absolute contraindications to laser vision correction. Keratoconus, a progressive disorder where the cornea thins and bulges into a cone shape, is one such condition. Performing laser surgery on an already weakened cornea can accelerate this thinning process. This potentially leads to a severe complication called ectasia, which causes significant vision distortion and loss.
Severe dry eye syndrome is a major concern because the procedure temporarily disrupts corneal nerves, reducing tear production and worsening existing symptoms. While mild dry eye can often be managed, severe cases or those linked to underlying systemic diseases can lead to prolonged discomfort, delayed healing, and poor final visual acuity. Any active eye infections, inflammation, or uncontrolled conditions like uveitis must be fully resolved before surgery is considered.
Systemic Health Conditions That Disqualify Candidates
A patient’s overall health plays a significant role in the safety and recovery of laser eye surgery, particularly regarding the body’s healing response. Individuals with autoimmune disorders, such as lupus, rheumatoid arthritis, or Sjogren’s syndrome, are typically not good candidates. These conditions involve a faulty immune response that can delay or impair the wound healing process required for corneal recovery. This compromised healing increases the risk of complications like infection and unpredictable visual outcomes.
Patients with uncontrolled diabetes are generally excluded from the procedure for two main reasons. First, fluctuating blood sugar levels can temporarily change the refractive index of the eye’s lens, causing the vision prescription to be unstable and inaccurate. Second, poorly managed diabetes impairs the body’s ability to heal and fight infection. This leads to a higher risk of post-operative complications and slow recovery of the corneal tissue.
Certain medications prescribed for chronic conditions can interfere with the healing process. Patients taking immunosuppressive drugs, including high-dose steroids, are often advised to postpone or avoid surgery due to the increased risk of infection and compromised healing. Hormonal fluctuations, such as those during pregnancy or nursing, can temporarily alter the eye’s shape and prescription due to fluid retention. Surgeons require patients to wait until a stable vision prescription returns, typically several months after discontinuing nursing, to ensure the accuracy and longevity of the surgical correction.
Age, Vision Stability, and Prior Surgical History
A minimum age requirement, usually 18 years old, is enforced to ensure the eye has reached its adult size and the vision prescription has stabilized. A stable prescription is a fundamental requirement for successful laser eye surgery. Ophthalmologists typically require documentation that the patient’s refractive error has not changed by more than 0.50 diopters for at least one to two years before the procedure.
If the prescription is still changing, surgery would correct the current error but would not prevent future changes, potentially requiring the patient to need glasses or contacts again soon after. This instability most commonly affects adolescents and young adults whose eyes are still developing.
A history of previous eye surgeries can present a challenge to laser eye surgery candidacy. Patients who underwent Radial Keratotomy (RK), an older surgical technique involving spoke-like incisions on the cornea, are often not suitable for LASIK. The RK incisions compromise the structural integrity of the cornea, making the creation of a LASIK flap risky. Potential complications include flap fragmentation or epithelial ingrowth. While LASIK may be contraindicated, an alternative surface-based procedure like PRK may sometimes be considered to safely refine the vision, as it avoids creating a corneal flap.