LASIK, or Laser-Assisted in Situ Keratomileusis, is a common laser eye surgery designed to enhance vision by reshaping the cornea, the clear front surface of the eye. This reshaping procedure adjusts how light enters the eye, allowing it to focus precisely on the retina. LASIK aims to reduce or eliminate the need for glasses or contact lenses by correcting common refractive errors.
Refractive Errors Corrected
LASIK addresses several types of refractive errors, which occur when the eye does not bend light properly. Nearsightedness, or myopia, is a condition where distant objects appear blurry while close objects remain clear. This occurs because the eyeball is too long or the cornea is too steeply curved, causing light to focus in front of the retina. LASIK corrects myopia by precisely flattening the central part of the cornea with a laser.
Farsightedness, or hyperopia, is the opposite, with nearby objects appearing blurry while distant vision may be clearer. In hyperopia, the eyeball is too short or the cornea is too flat, causing light to focus behind the retina. To correct this, LASIK steepens the curvature of the cornea.
Astigmatism is another common refractive error where vision becomes distorted or blurry at all distances due to an irregularly shaped cornea, which is more oval than round. LASIK treats astigmatism by selectively reshaping the cornea to make its surface more spherical.
Limits of Correction for Each Error
The extent to which LASIK can correct these refractive errors is typically measured in diopters (D), a unit indicating the optical power of a lens. For nearsightedness, LASIK can generally correct prescriptions up to -8.0 to -10.0 D, though some advanced laser technologies may treat up to -12.0 D. Patients with very high myopia beyond this range might find that LASIK cannot fully correct their vision or may carry increased risks.
For farsightedness, the typical correction range for LASIK is generally smaller, extending up to +4.0 to +5.0 D. Some clinics with advanced technology might treat up to +6.0 D. Correcting higher levels of hyperopia can be more challenging and may have a lower success rate or increased risk of complications.
For astigmatism, LASIK can typically correct up to 3.0 to 5.0 D, with some systems capable of correcting up to 6.0 D. Occasionally, up to 8.0 D might be possible depending on corneal characteristics. These limits are general guidelines; individual suitability depends on other factors.
Individual Factors Affecting Eligibility
Beyond the diopter limits of a prescription, several individual physiological factors influence a patient’s eligibility for LASIK and the degree of correction achievable. Corneal thickness is a primary consideration, as LASIK involves removing a small amount of corneal tissue to reshape it. Sufficient corneal tissue is necessary to ensure the structural integrity of the eye after the procedure. A minimum thickness of around 460 to 500 microns is generally considered necessary. If corneas are too thin, alternative procedures might be more appropriate.
Prescription stability is another important factor, requiring stability for at least one year, and ideally two years. Significant changes in prescription can indicate ongoing eye development or progression of a refractive error, affecting the long-term effectiveness of LASIK. Many surgeons prefer patients to be at least 18 years old, as vision tends to stabilize by then.
The size of a patient’s pupils can also influence eligibility, particularly regarding potential side effects. Patients with large pupils, especially in low light conditions, may experience visual disturbances such as glare or halos if the treated optical zone doesn’t cover the entire dilated pupil. While modern lasers have improved this, it remains a consideration.
Other existing eye conditions can preclude LASIK or limit its benefits. Severe dry eye can be exacerbated by LASIK, and conditions like keratoconus (a progressive thinning and bulging of the cornea), glaucoma, or cataracts generally disqualify candidates. Additionally, systemic health conditions, such as autoimmune disorders or uncontrolled diabetes, can affect the body’s healing process and increase the risk of complications. Pregnancy and nursing are also temporary contraindications due to hormonal fluctuations.
Expected Vision After LASIK
After LASIK, patients often experience a significant improvement in their vision, with many achieving excellent outcomes. Many achieve 20/20 vision or better, with over 90% reaching this clarity. About 99% of patients achieve 20/40 vision or better, meeting legal driving standards and significantly reducing their reliance on corrective lenses.
Patients should have realistic expectations; while clear vision is common, 20/20 vision is not guaranteed for everyone. Some individuals may still require glasses for certain activities, such as reading later in life due to presbyopia, which LASIK does not correct. Temporary side effects like night glare, halos, or dry eyes are common initially but typically diminish over weeks or months.