Types of Refractive Surgery: Complete Guide

Classification Overview

1. PRK (Photorefractive Keratectomy)
2. LASEK (Laser Subepithelial Keratomileusis)
3. Epi-LASIK (Epithelial LASIK)
4. LASIK (Laser In Situ Keratomileusis)
5. SMILE (Small Incision Lenticule Extraction / Refractive Lenticule Extraction)

Preoperative Assessment (Common to All)

• Stable refractive error (no change >0.5D for at least 12 months)
• Corneal topography and pachymetry
• Pupil size measurement
• Tear film assessment (Schirmer test)
• Endothelial cell count
• Exclusion of contraindications: dry eye syndrome, keratoconus, previous herpetic keratitis, glaucoma, macular degeneration, SLE, rheumatoid arthritis, immunocompromise, uncontrolled diabetes
• Informed consent including risks, alternatives, and expected outcome

1. PRK - Photorefractive Keratectomy

Refractive Range

• Myopia: up to -8.0D; Hypermetropia: up to +3.0D; Cylinder: up to 3.0D

Surgical Steps

1. Instill topical anesthetic drops
2. Mark the optical center and visual axis
3. Remove corneal epithelium (8-9 mm zone) using one of:
   • Mechanical scraping with blade/spatula
   • Automated Amoils epithelial brush
   • Dilute (20%) absolute alcohol applied for 20-30 seconds, then wiped
   • Trans-epithelial ablation (laser removes epithelium directly - Trans-PRK)
4. Apply excimer laser (193 nm argon-fluoride) to Bowman membrane and anterior stroma (30-60 seconds). Modern systems use eye-tracking that pauses if decentration occurs
5. Apply topical mitomycin-C 0.02% for 12-20 seconds to reduce haze risk (optional, used for higher corrections)
6. Copiously irrigate with BSS
7. Place a therapeutic bandage contact lens (BCL) for 4-5 days
8. Prescribe antibiotic + steroid + lubricant drops

Merits

• Safe for thin corneas (no stromal flap needed)
• No risk of flap complications
• Suitable for patients with epithelial basement membrane disease
• Lower risk of corneal ectasia than LASIK
• Good choice for contact sport athletes and military personnel
• No residual flap to dislocate with trauma

Demerits

• Significant postoperative pain for 3-5 days
• Slow visual recovery (1-3 months)
• Higher risk of subepithelial corneal haze (scarring)
• Cannot correct as high a degree of myopia as LASIK
• Risk of infection during epithelial healing phase
• Regression of effect possible

2. LASEK - Laser Subepithelial Keratomileusis

Refractive Range

• Same as PRK: Myopia up to -8.0D; Hypermetropia to +3.0D; Cylinder up to 3.0D

Surgical Steps

1. Instill topical anesthetic
2. Apply an epithelial trephine ring (well) onto the cornea to confine 20% absolute alcohol to the central 9 mm
3. Expose epithelium to alcohol for exactly 20-30 seconds (chemical separation at Bowman layer)
4. Lift the intact epithelial flap using a spatula/microhoe and fold it aside (typically nasally, leaving a hinge)
5. Apply excimer laser ablation to the exposed Bowman membrane/anterior stroma
6. Reposition the epithelial flap centrally (epi-on technique)
7. Apply BCL for 4-5 days
8. Postoperative antibiotic + corticosteroid drops

Merits

• Preserves epithelial flap - potentially reduces pain vs. PRK
• No stromal flap - avoids LASIK-related flap complications
• Suitable for thin corneas
• Useful for borderline dry eye

Demerits

• Postoperative pain (though slightly less than PRK)
• Slower recovery than LASIK
• Higher subepithelial haze risk (similar to PRK)
• Epithelial flap is often of poor quality and may be discarded anyway
• Alcohol exposure may cause epithelial toxicity
• Not ideal with significant pre-existing glaucoma

3. Epi-LASIK

Surgical Steps

1. Topical anesthetic instilled
2. Blunt epikeratome (oscillating or rotating) used to mechanically separate epithelium from Bowman layer at the subepithelial cleavage plane
3. Epithelial sheet folded to the side
4. Excimer laser ablation of anterior stroma
5. Epithelial flap repositioned (epi-on) or discarded (epi-off)
6. BCL placed; postoperative drops

Merits

• Avoids chemical alcohol toxicity on epithelium
• No stromal flap complications
• Suitable for thin corneas

Demerits

• Pain and slow recovery similar to LASEK/PRK
• Higher haze risk than LASIK
• Not ideal with significant glaucoma risk
• Epikeratome may cause irregular epithelial separation

4. LASIK - Laser In Situ Keratomileusis

Refractive Range

• Myopia: up to -10.0D; Hypermetropia: up to +3.0D (limited by corneal thickness); Cylinder: up to 3.0D

Surgical Steps

1. Comprehensive preoperative workup; topical anesthetic drops
2. Create the corneal flap using either:
   • Microkeratome (mechanical oscillating blade, 100-160 µm thickness), or
   • Femtosecond laser (IntraLase / FS200 / Ziemer: creates a gas bubble plane via photodisruption, giving more precise, planar flap - "all-laser LASIK" or "iLASIK")
3. Flap diameter: typically 8.5-9 mm; hinge left nasally or superiorly
4. Fold flap back to expose anterior stroma
5. Apply excimer laser ablation to stromal bed (customized treatment profile using wavefront-guided or topography-guided ablation)
6. Irrigation of the stromal bed with BSS
7. Reposition the flap carefully, ensure good alignment and no wrinkles
8. Dry the flap edge with a Merocel sponge; wait 1-2 minutes for flap adhesion
9. Instill antibiotic + lubricant drops; protective shield placed

Postoperative Care

• Topical antibiotics for 1 week
• Topical steroids for 1-2 weeks
• Frequent lubricating drops for dry eye

Merits

• Rapid visual recovery (functional vision by next day in most cases)
• Minimal postoperative pain (flap protects stroma)
• Low risk of corneal haze
• Wide correction range (higher myopia correctable vs. PRK)
• Wavefront-guided customization available (corrects higher-order aberrations)
• Reversible to some degree (flap can be re-lifted for re-treatment)
• High patient satisfaction rate

Demerits

• Flap complications: dislocation, striae (wrinkles), buttonhole flap, free cap, incomplete flap
• Risk of diffuse lamellar keratitis (DLK / "sands of the Sahara") - fine interface inflammatory infiltrates
• Dry eye syndrome (corneal nerves severed at flap, may persist 6-12 months)
• Epithelial ingrowth under the flap
• Risk of corneal ectasia (0.2-0.6%) - devastating thinning/bulging, especially with thin/ectatic corneas
• Flap can be dislodged years later by trauma
• Pressure-induced stromal keratitis (PISK) - secondary to steroid-induced IOP rise
• Requires adequate corneal thickness (minimum 250 µm residual stromal bed)
• Central toxic keratopathy (rare)
• Not suitable for thin corneas, contact sport athletes, or patients at high risk of ocular trauma

5. SMILE - Small Incision Lenticule Extraction (Refractive Lenticule Extraction / ReLEx)

Refractive Range

• Myopia: -1.0D to -10.0D; Myopic astigmatism: up to -3.0D. Cannot correct hypermetropia or pure hyperopic astigmatism.

Surgical Steps

1. Topical anesthetic; patient fixates on target light
2. Femtosecond laser (VisuMax, Zeiss) applied to create:
   • Posterior lenticule surface (deeper cut)
   • Anterior lenticule surface (shallower cut)
   • A small side-cut incision (2-4 mm arc at the periphery)
3. Surgeon inserts instruments through the small incision
4. Lenticule is dissected from surrounding stroma using spatulas (anterior and posterior interfaces separated)
5. Lenticule is grasped and extracted through the small incision
6. Corneal shape is altered by the tissue removed, correcting myopia (flattening the central cornea)
7. Interface irrigated; no flap replacement required
8. Postoperative antibiotic + steroid drops

Merits

• No flap - eliminates all flap-related complications
• Minimal disruption to anterior corneal nerves - less dry eye than LASIK
• Stronger corneal biomechanics (more structural integrity preserved)
• Only a 2-4 mm incision vs. 20 mm flap in LASIK
• Rapid recovery (nearly as fast as LASIK)
• Minimal pain
• Preferred for athletes or patients with trauma risk
• Less risk of ectasia (debated)

Demerits

• Cannot treat hypermetropia - limited to myopia and myopic astigmatism
• Cannot correct higher-order aberrations (no wavefront-guided or topography-guided customization)
• No cyclo-torsion compensation system
• Technically more demanding for the surgeon; steeper learning curve
• Fewer surgeons trained; fewer centers offer it
• Re-treatment is more difficult (requires PRK on top or converting to LASIK-like approach)
• Lower range for astigmatism correction vs. LASIK/PRK
• Slightly longer learning curve for lenticule dissection

6. Radial Keratotomy (RK)

Surgical Steps

1. Mark the optical zone (3-4 mm central clear zone)
2. 4-16 radial diamond blade incisions made from periphery toward center, stopping at the optical zone edge
3. Incision depth: 90-95% of corneal thickness
4. No laser used

Merits

• Does not require laser equipment
• Effective for low-moderate myopia

Demerits

• Significant diurnal variation in vision (hyperopic shift during the day)
• Progressive hyperopia over time
• Risk of corneal perforation
• Glare and halos
• Weakened corneal structural integrity
• Largely abandoned in favor of laser procedures

7. Astigmatic Keratotomy (AK) / Limbal Relaxing Incisions (LRI)

Surgical Steps

1. Mark steep axis of astigmatism from corneal topography
2. Place 1-2 arcuate incisions at the limbus or peripheral cornea along the steep meridian
3. Arc length and depth determined by nomogram (based on degree of astigmatism and patient age)

Merits

• Simple; no laser needed
• Useful adjunct during cataract/IOL surgery
• Low cost

Demerits

• Limited correction (typically < 3D astigmatism)
• Effect unpredictable and may regress
• Risk of glare, irregular astigmatism
• Overcorrection causes axis flip

8. Phakic IOL / ICL (Implantable Collamer Lens)

Types

• Anterior chamber iris-clip lens (Artisan/Verisyse): clipped to the iris at 3 and 9 o'clock positions
• Posterior chamber phakic IOL (ICL / EVO ICL, STAAR Surgical): inserted behind the iris and in front of the natural lens, supported in the ciliary sulcus

Refractive Range

• Myopia: up to -20D; Hypermetropia: up to +10D; Astigmatism: up to -6D (toric ICL)

Surgical Steps (ICL - most common)

1. Preoperative: measure anterior chamber depth (>2.8 mm required), endothelial cell count, WTW (white-to-white) to size the lens
2. Peripheral iridotomy (YAG laser or surgical PI) performed 1-2 weeks before to prevent pupillary block
3. Topical/regional anesthesia; small temporal clear corneal incision (~3.0-3.2 mm)
4. Viscoelastic injected into anterior chamber
5. ICL loaded and injected behind the iris using injector cartridge
6. Four footplates of ICL positioned in ciliary sulcus
7. Viscoelastic removed by aspiration
8. Wound self-sealing (no suture usually required)
9. Postoperative steroids + antibiotics; monitor IOP

Merits

• Preserves corneal tissue (no ablation)
• Excellent optical quality - preserves natural lens
• Reversible/explantable
• Corrects very high prescriptions beyond laser range
• Night vision often superior to laser procedures
• Rapid recovery

Demerits

• Surgical risks of intraocular procedure (infection, endophthalmitis)
• Risk of cataract formation (especially if vaulting too low)
• Pupillary block glaucoma (mitigated by iridotomy)
• Endothelial cell loss (especially with anterior chamber lenses)
• Dislocation/subluxation (iris-clip type)
• Requires adequate anterior chamber depth
• More expensive
• Risk of retinal detachment (high myopes)
• Oval pupil (iris-clip type)

9. Clear Lens Exchange (CLE) / Refractive Lens Exchange (RLE)

Refractive Range

• Virtually unlimited - high myopia, high hypermetropia, presbyopia

Surgical Steps

1. Biometry to calculate IOL power (IOLMaster, immersion US)
2. Topical anesthesia; 2.2-2.8 mm clear corneal incision
3. Continuous curvilinear capsulorhexis (CCC)
4. Phacoemulsification to emulsify and aspirate the crystalline lens
5. Irrigation/aspiration of cortex
6. IOL implanted into the capsular bag (monofocal / multifocal / trifocal / EDOF / toric options)
7. Wound sealed; postoperative drops

Merits

• Corrects very high prescriptions
• Eliminates possibility of future cataracts
• Premium multifocal/trifocal IOLs can correct presbyopia simultaneously
• Permanent, highly predictable outcome

Demerits

• Irreversible (natural lens accommodation permanently lost - significant in young patients)
• Risk of retinal detachment (especially in high myopes)
• Risk of posterior capsule opacification (PCO) - treatable with YAG laser
• All risks of intraocular surgery (endophthalmitis, cystoid macular edema, corneal decompensation)
• Loss of accommodation in younger patients (unless accommodating IOL used)
• Most expensive option

10. Intrastromal Corneal Ring Segments (ICRS / Intacs / Keraring)

Surgical Steps

1. Mark the center of the cornea
2. Femtosecond laser (preferred) or mechanical spreader creates tunnels in the mid-peripheral stroma at 70-80% corneal depth
3. ICRS segments (one or two, depending on correction required) inserted into the tunnels
4. Segments positioned within the tunnel; no sutures
5. Postoperative antibiotic drops

Merits

• Reversible (segments can be removed)
• No tissue removal
• Useful in keratoconus to regularize corneal shape
• Can delay/avoid corneal transplant

Demerits

• Limited refractive correction (-1D to -3D myopia)
• Risk of segment migration or extrusion
• Risk of corneal perforation during channel creation
• Infection (rare)
• Halos/glare around lights
• Not suitable for moderate-high myopia

Summary Comparison Table

• Kanski's Clinical Ophthalmology: A Systematic Approach, 10th ed. (Ch. 8 - Corneal and Refractive Surgery)
• The Wills Eye Manual, 7th ed. (Ch. 4.29 - Corneal Refractive Surgery Complications)
• Wills Eye Manual Table 4.29.1 - Refractive Surgery Characteristics (PRK vs. LASEK vs. Epi-LASIK vs. LASIK vs. SMILE)