Refractive Surgery: Overview

The cornea provides roughly two-thirds of the eye's total refractive power, while the crystalline lens provides the remainder along with accommodative function. Refractive surgery alters one of these two structures to change the eye's overall focusing power: corneal laser techniques (LASIK, PRK, SMILE) reshape the cornea, while lens-based approaches (implantable collamer lens, refractive lens exchange) add or replace an intraocular lens.

Corneal laser procedures ablate or extract stromal tissue to reshape anterior corneal curvature, interacting with the cornea's collagen architecture and biomechanical stability. Techniques preserving more anterior stroma (SMILE's flap-free approach) may offer structural advantages over flap-based LASIK in select patients. Lens-based ICL implantation avoids corneal tissue removal entirely, adding a posterior chamber lens instead — a network meta-analysis found this approach produces superior reduction of total higher-order aberrations, spherical aberration, and coma compared with corneal laser techniques.¹

Patients present electively seeking spectacle/contact lens independence rather than with a specific symptom complex. Preoperative evaluation (topography, pachymetry, pupil size, ocular surface health) determines candidacy and technique.

Key differentials/exclusions: forme fruste or subclinical keratoconus (critical exclusion given ectasia risk), active ocular surface disease, unstable refraction (recent contact lens wear, pregnancy), and cataract as the true cause of a refractive complaint in an older patient (better addressed by cataract surgery).

Candidacy assessment requires stable manifest/cycloplegic refraction, normal corneal topography/tomography excluding ectatic disease, adequate corneal thickness with sufficient predicted residual stromal bed, pupil size assessment (relevant to postoperative optical quality), and anterior chamber depth/angle assessment specifically for ICL candidacy.

Technique selection is individualized based on refractive error, corneal thickness/shape, pupil size, and preference. A network meta-analysis found ICL implantation demonstrated superior reduction of total higher-order aberrations, spherical aberration, and coma compared to all studied corneal laser techniques, suggesting preferential consideration in patients with high myopia or large pupils prioritizing optical quality.¹ For eyes at elevated ectasia risk, simultaneous accelerated corneal crosslinking with laser correction ("Xtra" procedures) produces comparable refractive/keratometric stability to laser correction alone, with no reported postoperative ectasia in susceptible eyes and some biomechanical advantage.²

• Excluding forme fruste keratoconus and ensuring adequate residual stromal thickness are the most critical ectasia-prevention steps
• ICL implantation showed superior HOA/aberration reduction versus all studied corneal laser techniques, especially relevant for high myopia or large pupils¹
• Simultaneous crosslinking ("Xtra" procedures) is an emerging strategy for ectasia-risk eyes with encouraging early data²
• Preoperative evaluation drives candidacy and technique choice far more than any presenting symptom
• Common pitfall: proceeding without adequately excluding forme fruste ectatic disease
• Common pitfall: not considering ICL for high-myopia/large-pupil patients prioritizing optical quality