LASIK, or Laser-Assisted in Situ Keratomileusis, is a widely performed surgical procedure that effectively corrects nearsightedness (myopia). Myopia is a common refractive error where light focuses in front of the retina instead of directly on it, causing distant objects to appear blurry. LASIK permanently reshapes the eye’s front surface, the cornea, using a cool-beam excimer laser. This technique reduces or eliminates the need for glasses or contact lenses for most patients seeking improved distance vision.
Correcting Nearsightedness Through Corneal Reshaping
Myopia occurs when the eye has an overly steep cornea or the eyeball is slightly too long. In either case, light entering the eye is bent too sharply, causing the focal point to land short of the retina. This misalignment creates the characteristic blur experienced when viewing distant objects.
The LASIK procedure corrects this by physically flattening the central curvature of the cornea. An excimer laser precisely removes microscopic amounts of tissue from the middle layer of the cornea, called the stroma, underneath a thin, hinged flap. By changing the curvature, the laser reduces the cornea’s refractive power, allowing incoming light rays to be focused further back.
This targeted flattening shifts the focal point backward to align onto the retina, resolving nearsighted vision. This mechanism is distinct from the correction of farsightedness (hyperopia), which requires the laser to remove tissue in a different pattern to steepen the central cornea. The precise control of the excimer laser allows for this individualized and permanent alteration of the corneal shape.
Who Qualifies for LASIK Correction
Determining eligibility for LASIK relies on meeting several strict criteria to ensure a safe and successful outcome. A primary factor is the stability of the patient’s prescription, which must not have changed significantly (typically no more than a half diopter change) for at least one to two years prior to the procedure. This stability ensures the correction made by the laser will be lasting, as the procedure does not stop the progression of myopia.
The severity of nearsightedness is a major consideration, as correction requires the removal of corneal tissue. While the FDA has approved LASIK for myopia up to \(-12.00\) diopters, many surgeons prefer to treat up to approximately \(-8.00\) diopters for the most predictable results. The higher the prescription, the more corneal tissue must be removed, which directly impacts safety.
Corneal thickness is the most important safety parameter in the screening process. The average cornea measures between 520 and 555 microns. The procedure must preserve a minimum residual stromal bed (RSB) of 250 to 270 microns to maintain the cornea’s structural integrity. This remaining tissue is essential to prevent a serious complication called corneal ectasia.
General health and ocular health also play a significant role in determining candidacy. Patients must be at least 18 years old. Those with certain systemic conditions, such as uncontrolled diabetes or active autoimmune diseases, may be disqualified due to compromised healing. Conditions affecting the eye, like severe chronic dry eye or existing infections, must be managed or resolved before the procedure.
The Patient Experience and Healing Timeline
The LASIK procedure is fast, typically requiring only 10 to 15 minutes to treat both eyes. Before the laser is used, the patient receives anesthetic eye drops, which numb the surface of the eye for a pain-free experience. During the procedure, a lid speculum gently holds the eyelids open, and the patient focuses on a target light while the laser works.
Immediately following surgery, patients may experience a gritty, scratchy, or watery sensation in their eyes, which often subsides within a few hours. Vision is usually noticeably improved right away, though it may be blurry or hazy as the corneal flap begins to heal. Patients are advised to go home and rest, keeping their eyes closed as much as possible for the first few hours. They are also given protective shields to wear while sleeping.
The healing timeline is quick, with many patients experiencing significant improvement in their vision within the first 24 to 48 hours. Most individuals return to work and resume light daily activities within a day or two of the procedure. While vision stabilizes significantly over the first month, the complete healing process and final visual results typically take between three and six months.