Refractive Surgery: Overview

Overview

Refractive surgery encompasses a range of corneal and lens-based procedures designed to reduce or eliminate a patient's dependence on spectacles or contact lenses by directly altering the eye's focusing power. Corneal laser-based techniques (LASIK, PRK, SMILE, and related variants) reshape the cornea, while lens-based approaches (implantable collamer lens, refractive lens exchange) add or replace an intraocular lens to achieve the desired refractive outcome. Selecting among these options requires individualized assessment of refractive error, corneal biometry, and patient-specific risk factors.

Epidemiology & Risk Factors

Candidacy for corneal laser refractive surgery depends on adequate corneal thickness and regularity, stable refraction, and the absence of contraindications such as keratoconus or other corneal ectatic disease, active ocular surface disease, or uncontrolled systemic conditions affecting wound healing. Patients with high myopia, thin corneas, or large pupils represent a population in which technique selection is particularly consequential for both safety (ectasia risk) and optical quality (higher-order aberrations, night vision symptoms). Implantable collamer lens (ICL) implantation, a lens-based alternative to corneal laser surgery, is particularly relevant for patients with high myopia or large pupils where optimal optical quality and minimization of higher-order aberrations are prioritized.¹

Pathophysiology

Corneal laser procedures work by ablating (PRK, LASIK) or extracting (SMILE) stromal tissue in a pattern calculated to reshape the anterior corneal curvature and correct the target refractive error, but this necessarily builds in some interaction with the cornea's underlying collagen architecture and biomechanical stability. Techniques that preserve more of the anterior stroma or corneal biomechanical strength (such as SMILE's small-incision, flap-free approach) may offer certain structural advantages over flap-based techniques (LASIK) in appropriately selected patients, though flap-based approaches remain highly effective and widely used. Lens-based approaches like ICL implantation avoid corneal tissue removal altogether, instead adding a refractive lens in the posterior chamber (between the iris and the natural crystalline lens) — a mechanism that a network meta-analysis found produces superior reduction of total higher-order aberrations, spherical aberration, and coma compared with corneal laser techniques including SMILE, LASIK, PRK, and other variants.¹

Clinical Presentation

Patients seeking refractive surgery typically present electively, motivated by a desire to reduce dependence on spectacles or contact lenses, rather than with a specific symptom complex. Preoperative evaluation focuses on refractive stability, corneal topography/tomography, pachymetry, pupil size, and ocular surface health, since these parameters — rather than any presenting symptom — determine both candidacy and technique selection.

Exam Findings

• Stable manifest and cycloplegic refraction over a defined period preceding surgery, typically required for candidacy
• Normal corneal topography/tomography without evidence of keratoconus or forme fruste ectatic disease
• Adequate corneal thickness with sufficient predicted residual stromal bed after any planned ablation or lenticule extraction
• Pupil size assessment, given its relevance to postoperative night vision symptoms and the comparative optical quality of different techniques¹
• Anterior chamber depth and angle assessment specifically for ICL candidacy, given the lens's posterior chamber location

Differential Diagnosis

• Forme fruste or subclinical keratoconus (a critical exclusion before any corneal laser procedure, given ectasia risk)
• Active or poorly controlled ocular surface disease (a relative contraindication or reason for optimization before proceeding)
• Unstable refraction (from recent contact lens wear, pregnancy, or other transient causes) warranting deferral of surgery
• Cataract as the primary cause of a refractive complaint in an older patient, better addressed by cataract surgery (potentially with an appropriate IOL) rather than corneal laser refractive surgery

Management

Technique selection is individualized based on refractive error magnitude and type, corneal thickness and shape, pupil size, and patient preference. Among corneal laser techniques (LASIK, femtosecond LASIK, PRK, LASEK, SMILE, and others) and ICL implantation, a network meta-analysis of eyes with myopia found ICL demonstrated superior reduction of total higher-order aberrations, spherical aberration, and coma compared to all other studied techniques, suggesting ICL implantation may be preferentially considered in selected patients — particularly those with high myopia or large pupils — where optimal optical quality is a priority.¹

For eyes with risk factors for post-refractive ectasia (e.g., relatively thin corneas or borderline topography), simultaneous accelerated corneal crosslinking combined with laser vision correction (so-called "Xtra" procedures — LASIK Xtra, PRK Xtra, SMILE Xtra) has emerged as a strategy to strengthen the cornea at the time of the refractive procedure. Recent literature indicates that combining crosslinking with these procedures produces refractive and keratometric stability comparable to laser correction alone, with no cases of postoperative ectasia reported in susceptible eyes across the reviewed studies, and some evidence of biomechanical advantage from the added crosslinking.²

Complications

• Postoperative dry eye, a common side effect of corneal laser refractive surgery, with a range of preventive and therapeutic strategies under active investigation
• Higher-order aberrations and reduced optical quality (glare, halos, reduced contrast sensitivity, particularly at night), varying by technique and patient-specific factors such as pupil size¹
• Post-refractive ectasia, a serious complication most associated with inadequate residual stromal thickness or undetected preoperative ectatic disease
• Under- or overcorrection requiring enhancement procedures
• ICL-specific risks, including angle-related complications, cataract formation, and endothelial cell density changes over time, given the lens's proximity to intraocular structures

Clinical Pearls

• Excluding forme fruste keratoconus and ensuring adequate residual stromal thickness are the most critical steps in preventing post-refractive ectasia
• ICL implantation demonstrated superior reduction in total higher-order aberrations, spherical aberration, and coma compared with all studied corneal laser techniques in a recent network meta-analysis, making it a strong option for patients prioritizing optical quality, particularly those with high myopia or large pupils¹
• Simultaneous crosslinking with laser vision correction ("Xtra" procedures) is an emerging strategy for eyes at elevated ectasia risk, with early evidence of comparable refractive outcomes and no reported ectasia in susceptible eyes, alongside possible biomechanical benefit²
• Preoperative evaluation (topography/tomography, pachymetry, pupil size, refractive stability) drives both candidacy and technique selection far more than any specific patient symptom
• Postoperative dry eye remains a common concern across corneal laser procedures, and prophylactic strategies are an active area of investigation

Common Pitfalls

• Proceeding with corneal laser refractive surgery without adequately excluding forme fruste keratoconus or other ectatic disease
• Failing to consider ICL implantation as an alternative in patients with high myopia or large pupils where optical quality is a high priority
• Assuming refraction is stable without adequate preoperative confirmation, risking early postoperative refractive drift
• Overlooking pupil size and other patient-specific factors that influence postoperative optical quality and technique selection
• Treating combined crosslinking-laser procedures as fully proven with the same long-term track record as laser correction alone, rather than as an evolving, still-maturing approach