The corneal refractive landscape

All corneal refractive surgery rests on one idea: changing the eye's power by reshaping the curvature of its first lens, the cornea. What distinguishes the techniques is not the optical goal — which is shared — but how it is achieved and which tissue is sacrificed to get there.

Two great families divide the field. The first removes tissue by excimer photoablation, sculpting the stroma directly according to a calculated profile: this is the principle of surface photoablation (PRK) and LASIK, which then differ only in how the stroma is accessed. The second does not photoablate: it cuts and extracts a lenticule of intact stroma using the femtosecond laser alone, without excimer — the logic of SMILE and, more recently, SILK.

Within the photoablative family, the decisive dividing line opposes surface techniques (ablation after epithelial removal) to lamellar techniques (ablation under a stromal flap). This distinction governs pain, recovery speed, postoperative dryness and — crucially — the amount of load-bearing tissue preserved, hence the risk of ectasia. This whole course is organised around that trade-off between immediate comfort and biomechanical integrity.