Types of Refractive Surgery - Complete Guide

Overview of Types

1. PRK (Photorefractive Keratectomy)

Steps

1. Preoperative assessment - Corneal topography, pachymetry, refraction, pupil size measurement; contact lenses discontinued 1-2 weeks prior.
2. Instill topical anesthetic - e.g., proparacaine 0.5%.
3. Epithelial removal - Using a sponge, automated brush (Amoils scrubber), blunt blade, alcohol (20% ethanol), or the excimer laser itself (Trans-PRK = single-step transepithelial).
4. Corneal drying - The Bowman layer and anterior stroma are dried and exposed.
5. Excimer laser ablation - Argon-fluoride excimer laser at 193 nm reshapes the anterior stroma (typically 30-60 seconds). Modern systems have eye-tracking and pupil centration.
6. Mitomycin-C (MMC) application - 0.02% MMC sponge applied for 15-30 seconds in higher corrections to reduce haze risk; then washed off.
7. Soft contact lens placement - Bandage contact lens placed for epithelial protection and comfort (typically removed at day 5-7 after re-epithelialization).
8. Postoperative drops - Topical antibiotics + steroids; lubricants for 3-6 months.

Refractive Range

• Myopia: up to -8.0 D | Hypermetropia: up to +3.0 D | Astigmatism: up to 3.0 D

Merits

• No stromal flap - eliminates flap-related complications (dislocation, striae, keratitis)
• Best choice for thin corneas
• Preferred for patients at high risk of eye trauma (athletes, military, contact sports)
• Suitable for epithelial basement membrane disease
• No risk of late flap displacement
• Better long-term corneal biomechanical stability than LASIK
• Lowest risk of corneal ectasia among laser procedures

Demerits

• Significant postoperative pain (3-5 days) until re-epithelialization
• Slower visual recovery (1-4 weeks for functional vision)
• Higher risk of subepithelial haze - especially in >-5D corrections without MMC
• Bandage contact lens required
• Steroid drops needed for months (risk of steroid-induced glaucoma and cataract)
• Lower correctable refractive range compared to LASIK

2. LASEK (Laser-Assisted Sub-Epithelial Keratectomy)

Steps

1. Preoperative preparation same as PRK.
2. Alcohol application - A trephine well is placed on the cornea; 20% absolute alcohol is applied for ~25-30 seconds to chemically loosen the epithelium.
3. Epithelial flap lifting - The softened epithelium is gently lifted as a hinged flap and folded to one side (usually 6 o'clock hinge).
4. Excimer laser ablation - Same as PRK.
5. MMC application if needed.
6. Epithelial flap replacement - The epithelial flap is repositioned centrally to act as a biological bandage.
7. Bandage contact lens placed.
8. Postoperative care as with PRK.

Refractive Range

• Same as PRK: Myopia -8.0 D, Hypermetropia +3.0 D, Astigmatism up to 3.0 D

Merits

• No stromal flap - avoids LASIK flap complications
• The preserved epithelial flap may reduce postoperative discomfort compared to PRK
• Suitable for thin corneas
• Good option for epithelial pathology cases

Demerits

• The alcohol step can damage epithelial cells, reducing the benefit of preservation
• Postoperative pain similar to (sometimes worse than) PRK
• Slower visual recovery than LASIK
• Risk of subepithelial haze similar to PRK
• Alcohol toxicity to Bowman layer possible
• Epithelial flap can disintegrate, making it functionally equivalent to PRK

3. Epi-LASIK

Steps

1. Preoperative assessment as standard.
2. Epi-keratome application - A specialized blunt blade oscillating separator cleaves the epithelium at the basement membrane level (avoiding alcohol toxicity).
3. Epithelial flap folded to the side.
4. Excimer laser ablation.
5. Epithelial flap repositioned (epi-on) or discarded (epi-off) based on surgeon preference.
6. Bandage contact lens + postoperative drops.

Refractive Range

• Same as PRK/LASEK range.

Merits

• Avoids alcohol toxicity compared to LASEK
• Mechanical separation is more reproducible
• No stromal flap complications
• Suitable for thin corneas

Demerits

• Not ideal with significant anterior corneal scarring or glaucoma
• Recovery profile similar to PRK/LASEK - prolonged pain and slow visual recovery
• Subepithelial haze risk persists
• Less commonly performed today given SMILE's emergence

4. LASIK (Laser-Assisted In Situ Keratomileusis)

Steps

1. Preoperative workup - Corneal topography (Pentacam/Orbscan), pachymetry (central corneal thickness must be >500 µm), refraction, dry eye assessment, dilated fundus exam.
2. Preoperative preparation - Topical antibiotic eye drops day before; anesthetic drops on table. Patient positioned supine under laser.
3. Suction ring application - A suction ring stabilizes the eye, raises IOP to ~65 mmHg.
4. Flap creation:
   • Microkeratome LASIK: Oscillating steel blade cuts a hinged flap (~100-160 µm thick, 8-9 mm diameter).
   • FS-LASIK (All-laser LASIK): Femtosecond laser (1053 nm infrared) creates a more precise, thinner flap (~90-110 µm). Safer, more predictable, preferred currently.
5. Flap lifting - The hinged flap is gently folded back, exposing the stromal bed.
6. Excimer laser ablation - 193 nm argon-fluoride laser ablates the stroma to reshape the corneal curvature. Eye tracking compensates for involuntary movements. Duration: 20-60 seconds.
7. Irrigation - The stromal bed is irrigated with BSS (balanced salt solution).
8. Flap replacement - The flap is carefully repositioned over the ablated bed; alignment marks confirm correct orientation.
9. Drying and sealing - A dry sponge gently dries the flap edges; the flap adheres by suction within minutes.
10. Postoperative regimen - Topical antibiotic + steroid drops for 1-2 weeks; artificial tears for 3-6 months; protective shield at night for one week.

Refractive Range

• Myopia: up to -10.0 D | Hypermetropia: up to +3.0 D | Astigmatism: up to 3.0 D

Merits

• Rapid visual recovery - functional vision within 24 hours, excellent by 1 week
• Minimal postoperative pain (the flap acts as a natural bandage)
• Minimal stromal haze
• Broadest refractive correction range among corneal procedures
• High patient satisfaction
• Wavefront-guided and topography-guided variants treat higher-order aberrations
• Reversibility - the stromal bed is accessible for re-treatment/enhancement

Demerits

• Flap complications (1-2%): dislocation (can be lifelong), striae, free cap, incomplete or irregular flap
• Dry eye - most common complication; due to severed corneal nerves; can persist 6-12 months
• Diffuse lamellar keratitis (DLK) - "sands of Sahara" - inflammatory reaction at flap interface; needs intensive steroids
• Epithelial ingrowth under the flap (1-2%)
• Corneal ectasia (0.2-0.6%) - progressive corneal thinning; more likely with thin corneas, forme fruste keratoconus, insufficient residual stromal bed
• Not ideal for thin corneas (<500 µm), epithelial dystrophies, severe dry eyes, contact sport athletes
• The flap creates a permanent structural weakness
• Bacterial keratitis (rare but serious)
• Pressure-induced stromal keratitis (PISK) with steroid use

5. SMILE (Small Incision Lenticule Extraction)

Steps

1. Preoperative assessment - Same as LASIK; refraction must be stable.
2. Topical anesthesia - Proparacaine drops; anxiolytics may be given.
3. Docking - The patient fixates on a target light; suction is applied to dock the eye to the femtosecond laser delivery system.
4. Femtosecond laser lenticule creation - The VisuMax femtosecond laser creates two curved intrastromal cuts defining a disc-shaped lenticule of stroma (the refractive lenticule) whose shape and thickness correspond to the refractive correction needed. A small 2-3 mm peripheral side-cut incision is simultaneously made.
5. Lenticule dissection - The surgeon inserts a spatula through the small incision and bluntly dissects the anterior plane of the lenticule, then the posterior plane, separating it from surrounding stroma.
6. Lenticule extraction - The freed disc of stroma is grasped with forceps and extracted through the 2-3 mm incision.
7. Irrigation - The intrastromal pocket is irrigated.
8. Postoperative drops - Topical antibiotics and steroids for 1-2 weeks; lubricants for dry eye.

Refractive Range

• Myopia: -1.0 D to -10.0 D | Myopic astigmatism up to 3.0 D
• Note: Currently approved only for myopia/myopic astigmatism in the US; not for hypermetropia

Merits

• No flap - eliminates all flap-related complications (dislocation, DLK, striae)
• Better corneal biomechanical stability than LASIK (peripheral anterior stromal collagen networks preserved, contributing ~60% of corneal tensile strength)
• Significantly less dry eye than LASIK due to fewer severed corneal nerves
• Higher patient satisfaction scores than LASIK in head-to-head studies
• Smaller incision reduces infection risk
• Minimal pain postoperatively
• Suitable for patients with mildly thin corneas unsuitable for LASIK
• Preferred for large-pupil patients prone to glare/halos with LASIK

Demerits

• Approved only for myopia/myopic astigmatism - cannot correct hypermetropia
• Steep learning curve for surgeons; initial cases have higher complication rates
• No eye-tracking system during lenticule creation (unlike excimer laser platforms)
• No cyclotorsion compensation - limits precision in high astigmatism
• Slower visual recovery at 1 month compared to LASIK (equalizes by 3 months)
• Lenticule extraction can be technically difficult; incomplete extraction possible
• Enhancement/re-treatment is complex - often requires conversion to PRK
• Higher intraoperative discomfort during tissue manipulation than flap lifting
• Back-scatter and light sensitivity more common at 1 month postop
• Limited customization (no wavefront-guided or topography-guided treatment currently)

6. Phakic Intraocular Lens (pIOL) Implantation

Two main types:

• Anterior chamber iris-claw (Artisan/Verisyse): Clipped to the anterior surface of the iris
• Posterior chamber phakic IOL (ICL / EVO ICL - Implantable Collamer Lens): Placed in the posterior chamber between the iris and the natural crystalline lens

Steps (ICL - most commonly performed today)

1. Preoperative assessment - Anterior chamber depth measurement (must be >2.8 mm), endothelial cell count, white-to-white corneal diameter, refraction.
2. Laser peripheral iridotomy (LPI) - Created 1-2 weeks before surgery (for non-KS-aquaport designs) to prevent pupillary block glaucoma. Newer EVO ICL has a central aquaport - LPI may be optional.
3. Anesthesia - Topical + optional intracameral lidocaine.
4. Small corneal incision (2.4-3.2 mm) created at limbus.
5. Viscoelastic injection into anterior chamber.
6. ICL loading into cartridge injector.
7. ICL injection through the incision into the anterior chamber.
8. Lens positioning - The ICL is rotated and placed behind the iris in the ciliary sulcus.
9. Viscoelastic removal - Thorough aspiration to prevent IOP spike.
10. Incision sealed (self-sealing or with suture).
11. Postoperative - IOP check at 2 hours; antibiotics + steroids for 4 weeks.

Merits

• Corrects very high myopia (-8 D to -20 D) or hypermetropia - beyond range of laser
• Excellent optical quality; no ablation = no higher-order aberrations from stroma
• Reversible - the lens can be removed or exchanged
• Natural lens is preserved - accommodation maintained
• No corneal tissue removed - useful when cornea is thin or abnormal
• Rapid visual recovery
• No dry eye (corneal nerves untouched)
• EVO ICL: no need for peripheral iridotomy

Demerits

• Intraocular procedure - carries risks of endophthalmitis, cataract, retinal detachment
• Elevated IOP / acute angle closure glaucoma (if undersized vault)
• Endothelial cell loss over time (especially anterior chamber designs)
• Requires adequate anterior chamber depth
• Cataract formation (~3% per patient year for early models, lower with EVO ICL)
• More expensive
• Requires LPI (for older designs)
• Not suitable for patients with shallow anterior chambers, glaucoma, or compromised endothelium

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

Steps

• Identical to standard phacoemulsification cataract surgery (steps as per cataract surgery)
• Corneal incision → viscoelastic → continuous curvilinear capsulorhexis → hydrodissection → phacoemulsification → cortex aspiration → IOL implantation → wound sealing

Merits

• Corrects very high refractive errors (e.g., >+5 D or < -12 D)
• Also corrects presbyopia (with multifocal/EDOF IOLs)
• No future cataract surgery needed
• Stable long-term result

Demerits

• Highest surgical risk among refractive options
• Retinal detachment risk - especially in high myopia (vitreous changes after lens removal)
• Endophthalmitis risk
• Loss of accommodation (if monofocal IOL)
• Dysphotopsia with multifocal IOLs
• Irreversible - natural lens cannot be replaced once removed

8. Radial Keratotomy (RK) / Astigmatic Keratotomy (AK) - Historical

Steps (RK)

1. Corneal marking of radial incision pattern
2. Diamond blade set to 90-95% corneal depth
3. 4-16 radial cuts from optical zone edge to limbus
4. Intraoperative pachymetry guidance

Merits

• No laser equipment needed
• Inexpensive
• Effective for mild myopia

Demerits

• Hyperopic shift over time (progressive flattening)
• Diurnal fluctuation in vision (morning myopic, afternoon hyperopic)
• Unpredictable results
• Weak corneal scars - risk of rupture with minor trauma
• Risk of infection, perforation, irregular astigmatism
• Largely abandoned in favor of laser procedures

Comparison Summary Table

Key Contraindications (All Laser Procedures)

• Unstable refractive error
• Keratoconus or forme fruste keratoconus
• Severe dry eye syndrome
• Active anterior segment disease (herpes simplex, blepharitis)
• Systemic diseases (SLE, rheumatoid arthritis, immunosuppression)
• Corneal thickness insufficient for planned ablation
• High expectations / unrealistic patients (requires thorough counseling)
• Glaucoma (relative - LASIK contraindicated; some surface ablation acceptable)

• Kanski's Clinical Ophthalmology: A Systematic Approach, 10th ed., Ch. 8 (Corneal and Refractive Surgery), pp. 284-303
• The Wills Eye Manual, 8th ed., Section 4.29 (Corneal Refractive Surgery Complications), p. 292
• PMC comparison of LASIK, Trans-PRK, and SMILE - 2025
• StatPearls: SMILE - NIH Bookshelf - Updated Feb 2024