Corneal refractive surgery is a type of eye procedure designed to correct common vision problems, reducing or eliminating the need for glasses or contact lenses. This surgery reshapes the cornea, the clear, outermost layer at the front of the eye. The main purpose is to allow light to focus properly on the retina, thereby improving visual clarity for individuals with various refractive errors.
Understanding Corneal Refractive Surgery
The human eye focuses light onto the retina, a light-sensitive layer at the back of the eye, to create clear images. The cornea’s shape is crucial for bending light as it enters the eye, allowing it to focus correctly on the retina. When the cornea’s curvature is irregular, light does not focus precisely, leading to blurry vision, a condition known as a refractive error.
Corneal refractive surgery addresses these issues by permanently altering the cornea’s curvature. This reshaping allows light to bend at the correct angle, directing it sharply onto the retina. The procedures commonly treat myopia (nearsightedness), where distant objects appear blurry; hyperopia (farsightedness), where close objects are unclear; and astigmatism, which causes distorted vision at all distances due to an irregularly shaped cornea.
Types of Procedures
Several types of corneal refractive surgery are available. These procedures use excimer lasers to precisely remove microscopic amounts of corneal tissue. The choice of procedure depends on factors like the patient’s specific eye condition, prescription, and corneal thickness.
LASIK
Laser-Assisted In Situ Keratomileusis, or LASIK, is a common refractive surgery. This two-step procedure begins with the creation of a thin, circular flap on the cornea’s surface using either a microkeratome or a femtosecond laser. This flap is then gently lifted to expose the underlying corneal tissue. An excimer laser reshapes the cornea. After reshaping, the corneal flap is repositioned, where it acts as a natural bandage, facilitating quick healing.
PRK
Photorefractive Keratectomy, or PRK, is a common laser eye surgery. Unlike LASIK, PRK does not involve creating a corneal flap. Instead, the thin outer layer of the cornea, known as the epithelium, is removed. An excimer laser then reshapes the exposed underlying corneal tissue. A bandage contact lens is placed over the eye to protect it while the epithelium regrows, which takes a few days.
SMILE
Small Incision Lenticule Extraction, or SMILE, is a newer and less invasive technique. This procedure uses a femtosecond laser to create a small, lens-shaped piece of tissue, called a lenticule, within the cornea. A tiny incision, 2 to 3 millimeters wide, is then made in the cornea, through which the surgeon removes the lenticule. This removal reshapes the cornea without the need for a large flap, which reduces the risk of dry eye and maintains corneal strength. SMILE is particularly effective for treating nearsightedness and astigmatism.
Who is a Candidate?
Determining eligibility for corneal refractive surgery involves several factors to ensure safety and the best possible outcome. Individuals should be at least 18 years old, with vision fully stabilized. A stable vision prescription for at least one year, and preferably two to three years, is required, as fluctuating prescriptions make surgical results less predictable.
Overall eye health is also assessed. Candidates should not have active eye diseases, such as cataracts, glaucoma, macular degeneration, or conditions like keratoconus. Adequate corneal thickness is also important, as the procedure involves reshaping the cornea. Certain systemic health conditions, such as some autoimmune diseases or uncontrolled diabetes, or being pregnant or nursing, also disqualify a person.
The Surgical Experience
Corneal refractive surgery begins with a thorough pre-operative assessment. This involves a comprehensive eye examination where the surgeon evaluates the patient’s overall eye health, corneal shape and thickness, pupil size, and refractive error. These tests ensure the eyes are suitable for the procedure and help create a personalized treatment plan.
During the procedure, taking about 15 to 20 minutes for both eyes, the patient receives numbing eye drops. A specialized instrument is then used to gently hold the eyelids open. Depending on the chosen procedure, a laser precisely reshapes the cornea. Patients may be given a mild sedative to help them relax during the process.
Immediately after surgery, patients may experience some mild discomfort, light sensitivity, or blurry vision. Protective eyewear is recommended to prevent accidental rubbing and protect the healing eyes. Visual improvement is noticed quickly for some procedures, with many patients achieving good vision by the next day, though full visual stabilization takes several weeks to months. Follow-up appointments are scheduled to monitor healing, and patients are advised to avoid activities like rubbing their eyes, swimming, or wearing eye makeup.
Possible Outcomes and Considerations
Following corneal refractive surgery, patients can expect a significant improvement in their vision, achieving independence from glasses or contact lenses. Many procedures aim for visual acuity of 20/40 or better. While the goal is clear vision, it is important to have realistic expectations, as the surgery does not guarantee “perfect” 20/20 vision for everyone and does not prevent age-related vision changes like presbyopia.
Common, temporary, side effects include dry eyes, which last for weeks to months, and visual disturbances such as glare, halos around lights, or light sensitivity, especially at night. These symptoms resolve as the eyes heal. More rare complications, occurring in less than one percent of cases, include infection, inflammation, undercorrection or overcorrection of vision, or issues with a corneal flap in LASIK procedures. While infrequent, serious complications like permanent vision loss are possible.