SMILE (Small Incision Lenticule Extraction) is a modern, minimally invasive form of laser vision correction that reshapes the cornea to correct nearsightedness and astigmatism. It offers reduced dependence on glasses or contact lenses for patients with stable prescriptions. The longevity of SMILE results depends on the stability of the corneal modification and the natural aging processes of the eye.
The Permanent Nature of Corneal Correction
The vision correction achieved through SMILE surgery is based on a permanent structural change to the cornea, the clear, dome-shaped front surface of the eye. During the procedure, a femtosecond laser is used to create a precise, lens-shaped piece of tissue called a lenticule within the middle layer of the cornea. This lenticule, which contains the exact refractive error to be corrected, is then removed through a tiny incision, typically less than four millimeters long. The physical removal of this tissue permanently changes the curvature of the cornea, allowing light to focus correctly on the retina.
Since the cornea cannot biologically regenerate this tissue, the reshaping of the eye is irreversible. The stability of the visual outcome is generally excellent after the initial healing period, which typically takes about six to twelve months. This structural modification ensures the corrected shape of the cornea remains for the rest of the patient’s life.
Differentiating Regression from Natural Aging
While the surgical change itself is permanent, a patient’s vision may appear to change over time due to two separate biological processes: true refractive regression and natural ocular aging.
True regression involves a slight return of the original refractive error, often occurring within the first year as the eye heals. This minor change is typically caused by the corneal epithelium subtly thickening in response to the new curvature. SMILE is associated with very low rates of clinically significant regression, often less than 2.0% in studies for mild to moderate myopia, making it a highly stable procedure. Any minor regression usually stabilizes quickly and is rarely enough to necessitate a retreatment.
The primary reason patients later notice changes in their vision is the non-surgical process of presbyopia. Presbyopia is the natural, age-related stiffening and hardening of the eye’s internal lens, which reduces its ability to change shape for near focus. This condition typically begins around age 40 to 45, requiring reading glasses for close-up tasks. Since SMILE only corrects the corneal shape for distance vision, it does not prevent this aging process. Furthermore, in later decades, the natural lens may begin to cloud, forming a cataract, which is another age-related change unrelated to the SMILE procedure.
Patient Factors Affecting Long-Term Results
The stability of the long-term visual outcome is influenced by several patient-specific factors present before the surgery.
Age and Prescription Stability
The patient’s age at the time of the procedure is a factor, as younger patients, particularly those in their late teens or early twenties, may still be experiencing natural eye growth. This ongoing growth can lead to further progression of nearsightedness, which is mistaken for the surgery failing. Specialists prefer to wait until the prescription has been stable for at least one year.
Severity of Myopia
The severity of the patient’s initial prescription also influences stability. Patients with very high degrees of myopia (corrections greater than -10 diopters) have a slightly higher risk of regression compared to those with mild prescriptions. Higher corrections require the removal of a thicker lenticule, which can result in a greater biological healing response from the cornea.
Ocular Health
A patient’s overall ocular health plays a part in the healing process and final stability. While SMILE is considered a favorable option for those with pre-existing mild dry eye, systemic conditions like uncontrolled diabetes can negatively affect healing and long-term corneal stability. A thorough preoperative screening ensures candidates have sufficiently thick and healthy corneas to maintain the new shape over time.