Types of Refractive Surgery: Merits and Demerits

I. SURFACE ABLATION PROCEDURES

1. PRK - Photorefractive Keratectomy

• No stromal flap is created - eliminates all flap-related complications (dislocation, buttonhole, incomplete flap)
• Preferred for thin corneas where LASIK would leave inadequate residual stromal bed
• No risk of flap trauma in contact sports or high-impact occupations (military, police, firefighters)
• Better long-term corneal biomechanical stability
• Suitable when epithelial pathology is present
• No interface haze or epithelial ingrowth possible (unlike LASIK)
• Favored by US military and federal agencies for decades

• Significant postoperative pain (3-5 days) until the epithelium regenerates
• Slower visual recovery (days to weeks vs. hours with LASIK)
• Higher risk of subepithelial haze (corneal scarring in the anterior stroma) - especially with high corrections
• Bandage soft contact lens required postoperatively for 3-5 days
• Regression of correction more likely than LASIK
• Prolonged steroid eye drop use needed (months) to suppress haze
• Not ideal with significant pre-existing glaucoma

2. LASEK - Laser Subepithelial Keratomileusis

• Preserves the epithelial sheet (compared to PRK where it is discarded), potentially reducing pain
• No stromal flap - same biomechanical advantages as PRK
• Useful in patients with thin corneas or epithelial pathology
• Avoids all stromal flap complications of LASIK
• Slightly less haze risk than PRK in some studies

• Postoperative pain and slower visual recovery - comparable to PRK
• Risk of alcohol toxicity to basal epithelial cells and Bowman layer
• Higher risk of subepithelial haze than LASIK
• The repositioned epithelial flap often does not survive, becoming necrotic
• Technically more demanding than PRK
• Not ideal with significant glaucoma

3. Epi-LASIK - Epithelial LASIK

• No chemical alcohol damage to epithelium
• No stromal flap - no flap complications
• Useful in thin corneas and epithelial pathology
• Potentially less haze than LASEK due to absence of alcohol toxicity

• Postoperative pain and slower visual recovery
• Higher risk of subepithelial haze compared to LASIK
• Not ideal with significant glaucoma or anterior corneal scarring
• The replaced epithelial flap may still not survive reliably
• Less commonly performed today; largely superseded by PRK or SMILE

II. LAMELLAR (STROMAL) PROCEDURES

4. LASIK - Laser-Assisted In Situ Keratomileusis

• Most commonly performed refractive procedure worldwide - excellent long-term track record
• Minimal postoperative pain (flap re-seals within hours, protecting nerve endings)
• Rapid visual recovery - most patients see well within 24-48 hours
• Minimal subepithelial haze (ablation is beneath Bowman layer)
• Wider refractive correction range than surface ablation
• Wavefront-guided and topography-guided customization available - ideal for irregular corneas and high astigmatism
• Accommodates both myopia and hyperopia effectively
• Eye-tracking and cyclotorsion compensation systems available

• Flap-related complications: dislocation (especially with trauma), buttonhole flap, incomplete flap, free cap, striae
• Epithelial ingrowth under the flap (late complication)
• Diffuse lamellar keratitis (DLK) - "Sands of Sahara" inflammation at the flap interface
• Higher risk of dry eye compared to PRK and SMILE (more corneal nerve disruption due to larger flap)
• Not ideal for thin corneas (requires adequate stromal bed thickness - minimum ~250 µm residual)
• Not suitable for corneas with epithelial dystrophies or severe dry eyes
• Risk of corneal ectasia if pre-existing subclinical keratoconus is missed
• Flap is a permanent structural weakness - trauma risk persists lifelong
• Not recommended for contact sports or certain occupations (military, police)
• Interface particles, infections (rare but serious)

5. SMILE - Small Incision Lenticule Extraction

• Flapless - eliminates all flap-related complications (dislocation, DLK, epithelial ingrowth)
• Only a tiny 2-4 mm incision vs. a 20 mm flap circumference in LASIK - far less corneal nerve disruption
• Less dry eye compared to LASIK (less disruption of sub-basal nerve plexus)
• Better corneal biomechanical stability than LASIK (cap is structurally stronger than a flap)
• No flap trauma risk - excellent for athletes and people at risk of eye trauma
• Minimal postoperative pain - comparable to LASIK
• Rapid visual recovery (slightly slower than LASIK, faster than PRK)

• Currently limited to myopia and myopic astigmatism in the US (hyperopia not approved)
• No wavefront-guided or topography-guided customization available
• Lacks an intraoperative eye-tracker and cyclotorsion compensation system
• Not ideal for high astigmatism where customized treatments would benefit
• Lenticule extraction can be technically challenging - risk of lenticule tear
• SMILE enhancements (re-treatments) are complex; retreatments are often done with surface PRK instead
• Not ideal for thin corneas or eyes with epithelial pathology
• Requires specialized expensive equipment; not all centers offer it
• Longer surgeon learning curve

III. INTRAOCULAR PROCEDURES

6. Phakic IOL Implantation (e.g., Visian ICL / EVO ICL)

• Can correct very high myopia (-3 D to -20 D) and hyperopia beyond laser surgery range
• No corneal tissue is removed - fully reversible/exchangeable
• Excellent visual quality (no optical aberrations introduced)
• Safe for thin corneas where laser surgery is contraindicated
• Rapid visual recovery
• Preserves accommodation (unlike RLE)

• Intraocular surgery carries risks of endophthalmitis, cataract formation, angle closure
• Risk of elevated intraocular pressure
• Risk of cataract with older angle-supported designs (posterior chamber ICLs have lower cataract rates)
• Requires adequate anterior chamber depth
• Permanent implant (though reversible, unlike corneal ablation is not trivially reversible)
• More expensive than laser procedures
• Not suitable after 45-50 years when presbyopia is developing (RLE preferred)

7. Refractive Lens Exchange (RLE) / Clear Lens Extraction

• Corrects very high refractive errors (myopia, hyperopia, astigmatism) including presbyopia
• Eliminates future cataract development (the lens has already been removed)
• Broad range of IOL options: multifocal lenses can achieve spectacle independence at all distances
• Permanent, predictable correction
• Suitable for patients over 45 with developing presbyopia

• Irreversible - accommodation is permanently lost in younger patients (presbyopia is induced)
• Risk of posterior capsule opacification (PCO) requiring YAG laser later
• Retinal detachment risk - notably higher in high myopes
• Intraocular surgery carries all surgical risks (infection, bleeding, corneal decompensation)
• Risk of posterior vitreous detachment and retinal complications
• Vitreous loss during surgery (uncommon)
• Loss of natural accommodation is a major downside in patients under 40

8. Conductive Keratoplasty (CK) and Corneal Inlays

• Merits: No laser, no tissue removal, minimally invasive
• Demerits: Results regress significantly over time; largely abandoned for primary correction

• Merits: Presbyopia correction without removing the crystalline lens
• Demerits: Risk of corneal haze, explantation required if complications arise; limited adoption

Quick Comparison Summary

• The Wills Eye Manual, Table 4.29.1 - Refractive Surgery Characteristics (PRK, LASEK, Epi-LASIK, LASIK, SMILE)
• Kanski's Clinical Ophthalmology, 10th ed., Chapter 8 - Corneal and Refractive Surgery
• LASIK vs. SMILE clinical comparison - PMC, 2025
• Mayo Clinic: Types of refractive laser surgery