Nearsightedness, or myopia, is a common refractive error where light focuses in front of the retina instead of directly on it. This causes distant objects to appear blurry, though close-up vision often remains clear. The underlying cause is typically an eyeball that is too long or a cornea that is too steeply curved. Modern laser eye surgery offers an effective solution by precisely reshaping the eye’s front surface. This procedure permanently alters the optics of the eye to restore clear distance vision.
The Mechanism of Correction
Correcting nearsightedness requires reducing the overall focusing power of the eye, which is primarily achieved by flattening the cornea. The procedure employs an excimer laser, which emits highly concentrated ultraviolet light. This laser light operates at a specific wavelength, typically 193 nanometers, which allows it to break the molecular bonds within the corneal tissue.
The process, known as photoablative decomposition, essentially vaporizes microscopic layers of tissue without causing thermal damage to the surrounding cells. For myopia correction, the laser is programmed to remove more tissue from the center of the cornea than the periphery. This targeted removal flattens the central curvature of the cornea, lessening its refractive strength. As a result, the incoming light rays are bent less sharply, enabling them to focus precisely on the retina.
Common Laser Surgery Methods
The three primary methods for laser vision correction—LASIK, PRK, and SMILE—all reshape the cornea but differ in how they access the tissue. Laser-Assisted In Situ Keratomileusis (LASIK) is the most frequently performed procedure. It involves creating a thin, hinged flap on the cornea’s surface, which is lifted to expose the underlying tissue. After the excimer laser performs the reshaping, the flap is immediately repositioned to serve as a natural bandage, resulting in the fastest visual recovery.
Photorefractive Keratectomy, or PRK, was the first laser method and remains a viable option, particularly for patients with thinner corneas. Instead of creating a flap, the surgeon removes the cornea’s outer layer of cells, the epithelium, before applying the excimer laser directly to the surface. The epithelial layer must then regenerate naturally over several days, which leads to a longer and more uncomfortable recovery period compared to LASIK. PRK recovery can take up to a week for functional vision, but the final visual outcome is comparable to LASIK.
Small Incision Lenticule Extraction (SMILE) eliminates the need for a flap altogether. This procedure uses a femtosecond laser to create a precise, lens-shaped piece of tissue, called a lenticule, within the cornea’s interior. The surgeon then removes this lenticule through a tiny incision. The “keyhole” approach offers biomechanical advantages and may reduce post-operative dry eye symptoms compared to LASIK. SMILE’s visual recovery time is intermediate, quicker than PRK but slightly slower than LASIK.
Determining Patient Suitability
Successful laser correction for nearsightedness depends on meeting several specific physiological and refractive criteria. A patient must typically be at least 18 years old because the eyes may still be changing in younger individuals. The patient’s glasses or contact lens prescription must have remained stable for a minimum of one year prior to the procedure. Significant fluctuations in prescription indicate ongoing eye growth, which would compromise the long-term result of the correction.
The overall health of the eye is also heavily scrutinized, as conditions like glaucoma, cataracts, or severe dry eye can interfere with healing and final outcomes. Corneal thickness is a major determining factor because the procedure works by removing tissue. Patients with corneas deemed too thin may not be candidates for LASIK, as it requires a certain residual thickness to maintain the structural integrity of the eye.
There are prescription limits to ensure a safe amount of tissue remains. For nearsightedness, the safe treatment range often extends up to -8 to -10 diopters, though this varies based on the laser technology and initial corneal thickness. A comprehensive evaluation of the cornea’s shape and health, often involving corneal topography, is required to determine the safest and most appropriate procedure.
Long-Term Visual Stability
The physical correction achieved by laser surgery is permanent because the removed corneal tissue does not grow back. For the majority of patients who met the criteria for prescription stability before surgery, the visual improvement is maintained for many years. Studies following patients for over a decade show a high rate of stable vision, confirming the durability of the procedure. A small percentage of individuals may experience a slight return of nearsightedness over time, a phenomenon known as regression.
If this change is significant enough to interfere with daily activities, an additional touch-up procedure called an enhancement may be performed, provided the cornea remains thick enough. Laser correction addresses the shape of the cornea, but it does not stop the natural aging process of the eye. Around age 40, most people develop presbyopia, the age-related difficulty in focusing on close objects. Laser eye surgery does not prevent or correct presbyopia, meaning reading glasses will still likely be necessary for near tasks.