What is the principle of laser excimer surgery?

People typically acquire external information through their eyes—the “windows to the soul”—making the eyes vitally important for everyone. However, certain unhealthy daily habits can easily lead to myopia (nearsightedness). Although myopia is now a common ophthalmic condition, its impact on eye health is significant. Laser-assisted in situ keratomileusis (LASIK), a type of excimer laser surgery, is one method used to correct myopia.

How Does Excimer Laser Surgery Work?

Excimer laser surgery uses an excimer laser to perform precise, refractive ablation on the corneal stromal layer beneath a created corneal flap. This reduces the curvature of the cornea within the pupillary zone, thereby correcting myopia. In simpler terms, the cornea is treated as a transparent optical material, and the laser reshapes it like a built-in corrective lens. This procedure can correct myopia ranging from −2.00 D to −20.00 D. Clinical experience to date shows that LASIK is the most commonly employed surgical technique for high myopia. However, it places stringent demands on corneal thickness and is suitable only for adults whose myopia has remained stable for at least two years. Potential complications include flap displacement or loss, epithelial ingrowth, corneal neovascularization, interlamellar foreign body retention, undercorrection, overcorrection, regression, and infection.

Preoperative Examinations for Excimer Laser Surgery

I. Visual Acuity Testing
Includes measurement of uncorrected visual acuity and best-corrected visual acuity with refractive correction.

II. Intraocular Pressure (IOP) Measurement
To rule out ocular hypertension and glaucoma.

III. Refractive Examination
Comprises three steps: automated refraction, clinical (subjective) refraction, and cycloplegic refraction. Accurate refractive measurements are critical to achieving optimal surgical outcomes.

IV. Anterior Segment and Fundus Examination
Focuses on corneal transparency, presence of corneal scars, lens clarity (to detect cataracts), and fundus evaluation for vitreous opacities or retinal pathology.

V. Wavefront Aberrometry
Assesses whether high-order aberrations—beyond low-order refractive errors such as myopia, hyperopia, and astigmatism—are present and significantly impairing visual quality. High-order aberration data are also collected for diagnostic and surgical planning purposes.

VI. Corneal Curvature Measurement
Helps exclude conditions such as keratoconus or flat cornea.

VII. Corneal Pachymetry
Especially important for patients with high myopia, as it determines the central corneal ablation depth. Preoperative counseling should clearly inform patients about this aspect.

VIII. Corneal Topography
Provides comprehensive assessment of the regularity and symmetry of the entire corneal surface, helping to identify abnormalities such as keratoconus.

After undergoing excimer laser surgery, diligent postoperative eye care is essential. While LASIK generally does not interfere with normal daily activities, patients must take special care of their eyes following surgery. Adequate rest, sufficient sleep, and consistent adherence to healthy visual hygiene practices are strongly recommended.