LASIK (Laser-Assisted in Situ Keratomileusis) is a highly effective surgical procedure for correcting nearsightedness, also known as myopia. Myopia occurs when the eye is too long or the cornea is too steeply curved, causing light to focus in front of the retina instead of directly on it, which makes distant objects appear blurry. LASIK permanently reshapes the cornea to fix this focusing error. For a vast majority of patients, LASIK offers a reliable solution that reduces or eliminates the need for prescription glasses or contact lenses.
The Mechanism of Myopia Correction
Myopia correction through LASIK addresses the focusing error using an excimer laser. This computer-controlled device emits precise pulses of ultraviolet light to vaporize microscopic amounts of corneal tissue. The reshaping process begins after a thin, hinged flap of the outer corneal tissue is created and gently folded back.
To correct nearsightedness, the excimer laser flattens the central curve of the cornea. Removing tissue from the center reduces the cornea’s light-bending power, making it less steep. This modification pushes the eye’s focal point backward, allowing light rays to converge directly onto the retina.
The amount of tissue removed is calculated based on the individual’s exact prescription, measured in diopters. Once the laser ablation is complete, the corneal flap is carefully repositioned, adhering naturally without stitches. The entire laser treatment phase is fast, often taking only a few seconds to a minute per eye, depending on the degree of correction required.
Determining Patient Suitability
While LASIK is highly effective, not every person with nearsightedness is a suitable candidate. A comprehensive evaluation is necessary to ensure the safety and long-term success of the vision correction. One important criterion is sufficient corneal thickness, as the laser removes tissue during reshaping.
The remaining cornea must be thick enough to maintain structural integrity and prevent complications like corneal ectasia. Since the treatment requires more tissue removal for higher myopic prescriptions, those with very thin corneas may be disqualified. Most surgeons aim to leave a minimum of 250 to 300 microns of tissue underneath the flap.
Another defining factor for candidacy is the stability of the patient’s prescription. Surgeons require that the refractive error has not changed significantly, typically by more than 0.5 diopters, for at least one year prior to surgery. This stability is why candidates must be at least 18 years old, as vision can still be changing in the late teens and early twenties.
Underlying eye health is also examined closely, as certain conditions can interfere with healing or compromise the final outcome. Ocular diseases such as active glaucoma, cataracts, or severe dry eye syndrome are a prerequisite for surgery. Systemic health issues like uncontrolled diabetes or autoimmune disorders can affect the body’s healing response, which may temporarily or permanently disqualify a patient.
Limitations and Residual Correction
Although LASIK can correct a wide range of nearsightedness, practical and safety limits exist. The maximum degree of myopia treatable is generally up to -12.00 diopters, though a surgeon’s specific limit may be lower depending on the technology used and the patient’s corneal thickness. Higher prescriptions demand the removal of more corneal tissue, which increases the risk of complications like corneal weakening.
In some cases, the initial LASIK procedure may result in a small remaining refractive error, known as residual correction. This may manifest as mild under-correction or a slight overcorrection. This minor residual error is often so slight that it does not affect daily life, but it can sometimes cause slight blurriness or require glasses for specific tasks like night driving.
If the residual refractive error is significant enough to impact vision quality, an enhancement procedure, or retreatment, may be considered. This secondary surgery involves relifting the original flap and applying another round of laser treatment to refine the corneal shape. Enhancement procedures are performed only after the patient still meets the necessary criteria, including having adequate corneal tissue remaining.