Enumerate and give brief descriptions of various lamellar keratoplasty

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types of lamellar keratoplasty ALK DALK DSEK DSAEK DMEK PDEK overview

I now have comprehensive information from both the textbook and web sources. Here is a thorough enumeration:

Types of Lamellar Keratoplasty

Lamellar keratoplasty (LK) refers to selective, partial-thickness corneal transplantation - replacing only the diseased layers while preserving healthy host tissue. This contrasts with penetrating keratoplasty (PK), which replaces the full corneal thickness. LK procedures are broadly divided into anterior (replacing front layers) and posterior/endothelial (replacing back layers).

Anterior Lamellar Keratoplasty (ALK)

What it is: The original form of lamellar surgery in which the anterior (front) portion of the corneal stroma is removed and replaced with a donor stromal disc of equivalent thickness. A manual blade or microkeratome is used to dissect the anterior stroma down to approximately the mid-stroma.

Indications: Anterior stromal opacities, superficial scars, recurrent pterygium, or localized thinning.

Key limitation: Interface haze between host and donor tissue is common, limiting visual outcomes. It has largely been superseded by DALK for full-anterior replacements.

Superficial Lamellar Keratoplasty (SLK)

What it is: A partial-thickness excision of the corneal epithelium and the most superficial one-third of the stroma. The endothelium and deep stroma are left intact as a bed for the donor tissue.

Indications:

Opacification of the superficial one-third of the stroma not caused by a potentially recurrent disease
Marginal corneal thinning or infiltration (e.g., recurrent pterygium, Terrien marginal degeneration, limbal dermoid, or other tumors)
Localized thinning or descemetocoele formation

Advantage: Simpler dissection than DALK; useful for peripheral or tectonic grafts.

(Kanski's Clinical Ophthalmology, 10th ed.)

Deep Anterior Lamellar Keratoplasty (DALK)

What it is: The corneal stroma is dissected almost entirely - down to the level of Descemet membrane (DM) - and replaced with donor tissue, while the host endothelium and DM are preserved. The "big bubble" technique (air injection to cleave DM from stroma) is a common approach.

Indications:

Disease involving the anterior ~95% of corneal thickness with a normal, healthy endothelium
Absence of breaks or scars in Descemet membrane (e.g., keratoconus without acute hydrops, superficial trauma, chemical injury)
Chronic inflammatory disease (e.g., atopic keratoconjunctivitis) with higher risk of endothelial rejection

Advantages:

No risk of endothelial rejection (the most immunogenic layer is not transplanted), though epithelial, sub-epithelial, or stromal rejection can still occur
Less astigmatism and a structurally stronger globe vs. PK
Greater availability of graft material since donor endothelial quality is irrelevant

Disadvantages:

Technically demanding and time-consuming with a high risk of Descemet perforation
Interface haze may limit best-corrected visual acuity

(Kanski's Clinical Ophthalmology, 10th ed.)

Posterior Lamellar Keratoplasty (PLK) / Deep Lamellar Endothelial Keratoplasty (DLEK)

What it is: The original posterior lamellar technique, first described by Gerrit Melles in 1998. A disc of posterior corneal stroma, DM, and endothelium is replaced via a scleral pocket incision, without removing the host DM. Considered the precursor to DSEK and DSAEK.

Status: Now largely of historical interest, replaced by DSEK/DSAEK and DMEK due to better techniques for tissue preparation and insertion.

Descemet Stripping Endothelial Keratoplasty (DSEK)

What it is: The host DM and endothelium are stripped and removed (Descemet stripping), and a manually prepared posterior donor disc (DM + endothelium + thin posterior stroma, typically 100-200 µm thick) is inserted through a small corneal incision and positioned against the posterior cornea using an air bubble.

Indications: Endothelial disease (e.g., Fuchs endothelial corneal dystrophy, bullous keratopathy).

Advantage over PLK: Does not require a scleral tunnel; simpler technique.

Descemet Stripping Automated Endothelial Keratoplasty (DSAEK)

What it is: A refinement of DSEK in which an automated microkeratome is used to prepare the donor posterior disc, producing a thinner and more uniform graft (typically 100-150 µm of posterior stroma + DM + endothelium). Currently the most widely performed endothelial keratoplasty technique worldwide.

Indications: Same as DSEK - endothelial failure (Fuchs dystrophy, bullous keratopathy, failed previous graft).

Advantages over PK:

Relatively little refractive change; structurally more intact globe
Faster visual rehabilitation (weeks vs. months)
Suturing minimized
Lower rejection rates (~12% vs. ~20% for PK)

Disadvantages:

Significant learning curve
Specialized equipment required
Visual outcome can be suboptimal due to graft thickness differences, interface irregularities, higher-order aberrations, or donor-recipient interface fibrosis
Endothelial rejection can still occur

(Kanski's Clinical Ophthalmology, 10th ed.)

Descemet Membrane Endothelial Keratoplasty (DMEK)

What it is: Developed by Melles in 2006. Only the donor Descemet membrane and endothelium are transplanted - no posterior stroma at all. The graft is an ultra-thin (~5-10 µm) scroll of DM + endothelium. It is introduced through a small incision and unrolled against the posterior cornea using air.

Indications: Same endothelial diseases as DSAEK, particularly Fuchs dystrophy.

Advantages over DSAEK:

Best visual outcomes (often 20/20 or better) and fastest visual recovery (1-2 weeks for initial clarity)
Lowest rejection rates of any keratoplasty
No donor stroma means near-normal optical interface

Disadvantages:

Technically the most demanding - the thin graft is very fragile and difficult to handle
Higher intraoperative complication rates (graft tears, dislocation) than DSAEK
Steep learning curve

Descemet Membrane Automated Endothelial Keratoplasty (DMAEK)

What it is: A modification of DMEK (described 2009) where a small rim of posterior stroma is retained at the periphery of the donor tissue, prepared using a microkeratome or femtosecond laser. The stromal rim makes the graft somewhat easier to handle than pure DMEK.

DMEK with Stromal Rim (DMEK-S)

What it is: Similar to DMAEK but the peripheral stromal rim is prepared manually rather than with a microkeratome. Described in 2010 as a compromise between DMEK handling ease and DMEK visual outcomes.

Pre-Descemet Endothelial Keratoplasty (PDEK)

What it is: A newer technique in which the donor tissue includes the thin pre-Descemet layer (Dua's layer, approximately 10 µm), DM, and endothelium. A type 1 big bubble is used to isolate this tissue. The pre-Descemet stroma provides added structural support compared to DMEK alone, making the graft easier to handle while still producing excellent visual outcomes.

Advantage: Easier to prepare and handle than DMEK while achieving comparable visual results.

Descemet Stripping Only (DSO) / Bowman Layer Transplantation

What it is: Emerging, non-graft approaches that deserve brief mention:

DSO (Descemetorhexis Without Endothelial Keratoplasty): In early Fuchs dystrophy, simply stripping a central disc of diseased DM allows peripheral endothelial cells to repopulate the center over weeks-months, without any donor tissue. Suitable only for mild-moderate Fuchs with good peripheral endothelial reserve.
Bowman Layer Transplantation: An isolated Bowman layer (without epithelium or stroma) is transplanted into deep corneal stroma for advanced keratoconus to flatten and stiffen the cornea, delaying or avoiding PK.

Summary Table

Procedure	Layer(s) Replaced	Primary Indication
SLK	Epithelium + superficial stroma	Superficial opacities, marginal thinning
ALK	Anterior stroma (mid-depth)	Anterior stromal disease
DALK	Stroma (down to DM)	Keratoconus, anterior stromal disease with healthy endothelium
DSEK	Post. stroma + DM + endothelium (manual prep)	Endothelial failure
DSAEK	Post. stroma + DM + endothelium (automated prep)	Endothelial failure
DMEK	DM + endothelium only	Endothelial failure (best outcomes)
DMAEK	DM + endothelium + peripheral stromal rim (automated)	Endothelial failure
DMEK-S	DM + endothelium + peripheral stromal rim (manual)	Endothelial failure
PDEK	Pre-Descemet layer + DM + endothelium	Endothelial failure
DSO	None (native repopulation)	Early Fuchs dystrophy
Bowman layer transplant	Bowman layer into stroma	Advanced keratoconus

The general trend in lamellar surgery has been toward increasingly selective tissue replacement - from ALK (replacing bulk anterior stroma) to DMEK (transplanting only an ultra-thin membrane) - in pursuit of lower rejection rates, faster recovery, and better visual outcomes.

Source: Kanski's Clinical Ophthalmology: A Systematic Approach, 10th ed., pp. 281-296; supplemented by EyeWiki and Cornea Research Foundation of America.

enlist various types of refractive surgery with its merits and demerits in details

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types of refractive surgery LASIK PRK SMILE LASEK RK phakic IOL merits demerits comparison

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Types of Refractive Surgery - Merits and Demerits

Refractive surgery corrects errors of refraction (myopia, hypermetropia, astigmatism, presbyopia) by altering the curvature/power of the cornea or replacing/supplementing the crystalline lens. Procedures are broadly classified into three categories:

A. CORNEAL ABLATIVE (LASER) PROCEDURES

These use an argon-fluoride excimer laser (193 nm UV) to precisely ablate corneal stroma and reshape the anterior curvature.

1. Photorefractive Keratectomy (PRK)

Mechanism: The corneal epithelium is removed (by blade, brush, spatula, dilute alcohol, or the excimer laser itself), and the underlying Bowman membrane/anterior stroma is directly ablated by the excimer laser to flatten (myopia) or steepen (hyperopia) the cornea.

Refractive range: Sphere -8.0 D to +3.0 D; cylinder up to 3.0 D

Merits:

No corneal flap is created - avoids all flap-related complications entirely
Suitable for thin corneas where creating a LASIK flap would leave insufficient residual stromal bed
Useful in patients with anterior corneal epithelial pathology (anterior basement membrane dystrophy, recurrent corneal erosion)
Preferred in patients at risk of ocular trauma (military, contact sports) - no flap to dislocate
Structurally stronger post-operative cornea than LASIK
Lower risk of post-operative ectasia than flap-based procedures
No risk of diffuse lamellar keratitis (DLK)

Demerits:

Significant postoperative pain for 2-4 days (raw nerve endings exposed at Bowman membrane)
Slower visual recovery (days to weeks vs. days with LASIK)
Higher risk of subepithelial/anterior stromal corneal haze, especially for corrections >5 D (mitigated by intraoperative mitomycin C 0.02%)
Longer dependence on topical steroids (months) to prevent haze regression
Risk of steroid-response glaucoma from prolonged steroid use
Not ideal for patients requiring immediate return to work or driving

(Wills Eye Manual, 5th ed.; Kanski's Clinical Ophthalmology 10th ed.)

2. Laser Subepithelial Keratomileusis (LASEK)

Mechanism: A 20% dilute ethanol solution is applied to the epithelium via a well/marker ring, chemically loosening it from Bowman's layer. The epithelial sheet is reflected to one side as a flap, the stroma is ablated with an excimer laser, and the epithelial flap is then repositioned centrally. A bandage contact lens is placed.

Refractive range: Same as PRK (-8.0 D to +3.0 D; cylinder up to 3.0 D)

Merits:

Preserves the epithelial flap, which acts as a natural bandage - potentially less pain than PRK
No stromal flap - avoids stromal flap healing issues and DLK
Suitable for thin corneas
The preserved epithelium may reduce post-op haze

Demerits:

Post-operative pain and slow visual recovery similar to PRK
The preserved epithelial flap is often devitalized by the alcohol and may not confer significant healing benefit
Higher subepithelial haze risk than LASIK
Alcohol toxicity to underlying stroma and limbal cells is a concern
Technically more cumbersome than standard PRK

3. Epi-LASIK

Mechanism: A blunt-blade epi-keratome (Epi-K device) mechanically separates the epithelium from Bowman's layer (avoiding chemical toxicity). The epithelial sheet is moved aside, stroma ablated, and the epithelium either replaced (epi-on) or discarded (epi-off).

Refractive range: Same as PRK (-8.0 D to +3.0 D; cylinder up to 3.0 D)

Merits:

Avoids alcohol toxicity of LASEK
No stromal flap complications
Suitable for thin corneas
Mechanical separation is more predictable than chemical in LASEK

Demerits:

Post-operative pain and slow visual recovery (similar to PRK/LASEK)
Higher haze risk than LASIK
Not ideal in patients with significant glaucoma (IOP spike risk with keratome pressure)
Epi-keratome device adds cost and technical requirements

4. Transepithelial PRK (TransPRK / No-Touch PRK)

Mechanism: A single-step, fully automated procedure where the excimer laser removes both the epithelium and ablates the stroma in one pass, without any mechanical or chemical epithelial manipulation. No blade, alcohol, or manual epithelial removal.

Merits:

True "no-touch" technique - minimal corneal trauma
Faster than standard PRK (one laser pass)
Suitable for thin corneas, corneal scars, anterior erosion syndromes
Good for patients who are anxious about instruments touching their eye
No flap complications

Demerits:

Pain and slow recovery as with other surface ablation procedures
Haze risk (mitigated with mitomycin C)
Requires specialized laser software (Schwind Amaris 1050RS and similar platforms)

5. LASIK (Laser In Situ Keratomileusis)

Mechanism: A hinged partial-thickness corneal flap (~110-160 µm thick) is created using either a mechanical microkeratome or a femtosecond laser (Femto-LASIK/iLASIK). The flap is lifted, the underlying stroma is ablated by the excimer laser, and the flap is repositioned without sutures. The flap adheres by surface tension and stromal healing.

Refractive range: Sphere -10.0 D to +3.0 D; cylinder up to 3.0 D

Merits:

Minimal post-operative pain (stroma has fewer exposed nerve endings under flap)
Rapid visual recovery - patients typically see well within 24-48 hours
Minimal subepithelial haze (stroma not directly exposed to air/UV)
Both eyes can be treated at the same session
Wide refractive range - corrects higher myopia than surface ablation
Femtosecond laser flap creation (Femto-LASIK) is more precise and reproducible than microkeratome, with thinner/more uniform flaps

Demerits:

Flap complications: dislocation/displacement (trauma, even years later), wrinkling/striae, buttonhole flap, free cap, incomplete flap
Diffuse lamellar keratitis (DLK) - "Sands of the Sahara" - sterile inflammatory cells in flap interface (occurs within 5 days)
Epithelial ingrowth under the flap
Dry eye - post-LASIK keratoneurotrophic dry eye is very common (corneal nerve transection); may persist 6-12 months
Post-LASIK ectasia - corneal weakening and bulging, especially if residual stromal bed <250-300 µm or if pre-existing subclinical ectasia (forme fruste keratoconus)
Reduced corneal sensation for months
Contraindicated in thin corneas (pachymetry <500 µm)
Central toxic keratopathy (rare)
Structural weakening of cornea compared to PRK

(Wills Eye Manual, Kanski's 10th ed.)

6. Femtosecond LASIK (Femto-LASIK / All-Laser LASIK / iLASIK)

Mechanism: Same as LASIK but the microkeratome is replaced entirely by a femtosecond laser (IntraLase, VisuMax, FEMTO LDV) for flap creation, allowing programmable flap diameter, depth, hinge position, and edge architecture.

Merits over standard LASIK:

More accurate and reproducible flap thickness
Lower risk of buttonhole flap, free cap, or incomplete flap
Planar flap edges allow better flap adhesion
Can create thinner flaps, preserving more residual stromal bed
Lower rate of epithelial ingrowth

Demerits:

Higher cost than microkeratome LASIK
Transient light sensitivity syndrome (TLSS) - rare but unique to femtosecond flap creation
Opaque bubble layer (OBL) can complicate eye tracking during ablation
All other LASIK demerits still apply

7. SMILE (Small Incision Lenticule Extraction)

Mechanism: A femtosecond laser (Carl Zeiss VisuMax/VisuMax 800 for SMILE Pro) cuts two parallel intrastromal plane cuts within the intact cornea, carving a lens-shaped disc of stroma (the lenticule). The lenticule is then mechanically extracted through a small 2-4 mm arcuate incision using special forceps, without any flap.

Refractive range: Sphere -10.0 D to -1.0 D; cylinder up to 3.0 D (hyperopia correction not currently approved for SMILE)

Merits:

No corneal flap - eliminates all flap-related complications (dislocation, striae, DLK, epithelial ingrowth)
Significantly less dry eye than LASIK (anterior corneal nerves largely preserved; only the small incision severs some nerve fibers)
Minimal post-operative pain
Rapid visual recovery (comparable to LASIK)
More biomechanically stable than LASIK (intact anterior cap)
Good for patients with active lifestyles and contact sports
Single laser platform (no separate excimer laser step)

Demerits:

Currently corrects only myopia and myopic astigmatism - not approved for hyperopia
Cannot be easily enhanced/retreated if undercorrection occurs (a PRK or conversion to a LASIK-like flap procedure may be needed)
Requires specialized femtosecond laser platform (VisuMax)
Steep learning curve; extracting the lenticule requires specific surgical technique
Slightly slower visual recovery in early post-op period compared to LASIK for some patients
If lenticule tears, salvage requires conversion to surface ablation
Higher cost; not universally available

(Kanski's Clinical Ophthalmology 10th ed.; Wills Eye Manual)

B. CORNEAL INCISIONAL PROCEDURES

These use mechanical incisions to alter corneal curvature without laser ablation.

8. Radial Keratotomy (RK)

Mechanism: Multiple (4-16) radial, spoke-like deep incisions (90-95% depth) are made in the peripheral cornea with a diamond blade, centrifugally from a central optical zone. This weakens the peripheral cornea, causing it to bow outward, which flattens the central cornea and reduces myopia.

Merits:

Does not require expensive laser equipment
Effective for low-to-moderate myopia (up to approximately -5.0 D)
Reversible to some extent (suturing incisions can partially reverse effect)
No corneal tissue removed

Demerits:

Significant diurnal fluctuation in vision (vision better in morning, worsens through the day)
Hyperopic shift over years - the cornea continues to flatten progressively with age
Risk of corneal perforation during procedure
Globe weakening - the deep incisions permanently weaken the cornea; risk of rupture with minimal trauma
Irregular astigmatism
Endothelial cell loss if incisions are too deep
Pain, photophobia post-procedure
Largely replaced by excimer laser procedures; now of historical/limited use

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

Mechanism: Paired arcuate incisions are made in the steep corneal meridian (at the limbus for LRI, or more centrally for AK) to flatten it, correcting astigmatism. The incisions relax the steep axis and couple-shift flattening to the flat axis.

Merits:

Simple technique; can be done at the time of cataract surgery
No laser equipment required
Effective for low-to-moderate astigmatism (up to ~3.0 D with AK)
LRI at limbus has minimal effect on the visual axis

Demerits:

Less precise than toric IOLs or excimer laser for astigmatism correction
Unpredictable results (age-dependent, variable wound healing)
Risk of overcorrection/undercorrection
Diurnal variation (like RK)
Not suitable for high astigmatism

10. Laser Thermal Keratoplasty (LTK) / Conductive Keratoplasty (CK)

Mechanism: LTK uses a holmium:YAG laser applied to the mid-peripheral corneal stroma in a ring pattern, causing collagen shrinkage. CK uses radiofrequency energy delivered via a thin probe in a ring pattern. Both steepen the central cornea to correct hyperopia and presbyopia.

Merits:

Non-ablative, no tissue removed
CK is office-based, simple technique
Good for mild hyperopia and presbyopia (monovision approach)
Rapid procedure, minimal recovery

Demerits:

Regression over time - effect diminishes as collagen remodels
Not durable; many patients require retreatment or return to glasses
Irregular astigmatism possible
Not suitable for high hyperopia or myopia
LTK largely abandoned; CK also declining with advent of laser procedures

C. LENS-BASED REFRACTIVE PROCEDURES

For refractive errors outside laser range or with inadequate corneal thickness.

11. Phakic Intraocular Lens (pIOL) Implantation

A refractive lens is implanted inside the eye while the natural crystalline lens is preserved ("phakic" = natural lens retained).

a) Anterior Chamber Iris-Claw / Iris Clip Lens (Artisan / Verisyse)

Mechanism: A rigid PMMA lens is attached to the anterior iris stroma at 3 and 9 o'clock (clipped onto mid-peripheral iris). Positioned in the anterior chamber.

Merits:

Wide refractive range - corrects very high myopia (up to -25 D) beyond laser range
Reversible - can be explanted
Preserves accommodation (natural lens retained)
No corneal tissue ablated; corneal topography unchanged
No regression of effect over time

Demerits:

Risk of endothelial cell loss (lens close to endothelium; minimum endothelial count required)
Pupillary block glaucoma - requires peripheral iridectomy
Subluxation or dislocation (attachment loss from iris)
Oval pupil from iris distortion
Risk of cataract formation
Requires general or peribulbar anaesthesia
Cumbersome with large lens size

b) Posterior Chamber Phakic IOL - Implantable Collamer Lens (ICL / EVO ICL, Visian ICL)

Mechanism: A flexible collamer (collagen/HEMA copolymer) lens is inserted through a small (3 mm) temporal incision and positioned behind the iris, in the ciliary sulcus, in front of the natural crystalline lens. A central aqueous port (KS-Aquaport in EVO ICL) allows aqueous to flow without peripheral iridectomy.

Refractive range: -20 D to +10 D; toric versions correct astigmatism up to 6 D

Merits:

Excellent visual quality - no corneal aberrations introduced
Wide range - treats very high myopia/hyperopia beyond laser limits
Preserves accommodation
Reversible and exchangeable
Better biocompatibility than anterior chamber lenses
No risk of regression
Patient satisfaction among the highest of any refractive procedure
EVO ICL does not require peripheral iridectomy (central aqueous port)
Phakic IOLs showed superior safety and patient satisfaction vs. excimer laser for high myopia in a systematic review (PMC10726981)

Demerits:

Intraocular surgery - higher risk profile than laser procedures
Cataract formation (crystalline lens contact/crowding)
Pupillary block glaucoma (especially older designs without central port)
Angle closure or raised IOP
Endothelial cell loss (less than anterior chamber IOLs)
Requires precise sulcus-to-sulcus sizing (too small = pupillary block; too large = cataract, angle damage)
Expensive; requires trained surgeon and specialized lens sizing
Retinal detachment risk in high myopes (independent of surgery)

12. Refractive Lens Exchange (RLE) / Clear Lens Extraction (CLE)

Mechanism: The natural crystalline lens is removed (identical procedure to cataract surgery) and replaced with a calculated intraocular lens (IOL) - monofocal, toric, multifocal, or EDOF (extended depth of focus) - to achieve the desired refraction.

Merits:

Virtually unlimited refractive range (any degree of myopia, hyperopia, astigmatism correctable)
Eliminates risk of future cataract
Toric IOLs correct astigmatism precisely
Multifocal/EDOF IOLs can provide spectacle independence at near and distance (presbyopia correction)
Best option for patients >45-50 years (where accommodation is already lost)
Predictable, stable, no regression

Demerits:

Permanent loss of accommodation (young patients become fully presbyopic) - requires monovision or multifocal IOL planning
Risk of retinal detachment - significantly elevated in high myopes (vitreous loss of support after lens removal)
All risks of intraocular surgery: infection (endophthalmitis), posterior capsule opacification, cystoid macular edema, IOL dislocation, raised IOP
Multifocal IOLs can cause dysphotopsias (halos, glare, starbursts) - may be intolerable in some patients
Not reversible (natural lens cannot be replaced)
Premium multifocal/EDOF IOLs are expensive

13. Corneal Inlay Procedures (e.g., KAMRA Inlay / Raindrop)

Mechanism: A small aperture inlay (KAMRA, 3.8 mm with central 1.6 mm aperture) is implanted intrastromally in the non-dominant eye to increase depth of focus for near vision, treating presbyopia. The Raindrop inlay changed corneal curvature centrally.

Merits:

Reversible - inlay can be explanted
Addresses presbyopia without glasses
Does not alter corneal ablation in the fellow eye
Good intermediate-near vision

Demerits:

Regression of effect over time
Risk of corneal haze, fibrosis around inlay
Some patients experience glare/halo
Night vision disturbance
Raindrop inlay was withdrawn from the market (FDA recall, 2018) due to corneal haze
KAMRA also no longer commercially available in some markets
Limited to presbyopia correction only

Summary Comparison Table

Procedure	Refractive Range	Reversible	Key Merit	Key Demerit
PRK	-8 to +3 D	No	Flapless, thin corneas	Pain, haze, slow recovery
LASEK	-8 to +3 D	No	Chemical epithelial flap	Pain, similar to PRK
Epi-LASIK	-8 to +3 D	No	No alcohol toxicity	Pain, slow recovery
TransPRK	-8 to +3 D	No	No-touch, single step	Pain, haze
LASIK	-10 to +3 D	No (flap permanent)	Fast recovery, minimal pain	Flap complications, dry eye, ectasia
Femto-LASIK	-10 to +3 D	No	Precise flap, safer than microkeratome LASIK	Cost, TLSS
SMILE	-10 to -1 D	No	Flapless, less dry eye	Myopia only, limited enhancement options
Radial Keratotomy (RK)	-1 to -5 D	Partial	No equipment needed	Diurnal variation, hyperopic shift, globe weakening
AK / LRI	Astigmatism up to 3 D	No	Simple, intraoperative	Unpredictable, regression
CK / LTK	Low hyperopia/presbyopia	No	Non-ablative	Regression, declining use
Iris-claw pIOL	Up to -25 D	Yes	Very high myopia, preserves lens	Endothelial loss, glaucoma risk
ICL (EVO)	-20 to +10 D	Yes	Best quality, very high range	Intraocular risks, cataract
RLE / CLE	Unlimited	No	Any error, eliminates cataract	Loss of accommodation, RD risk

Sources: Kanski's Clinical Ophthalmology: A Systematic Approach, 10th ed. pp. 284-310; Wills Eye Manual, Table 4.29.1; Harrison's Principles of Internal Medicine, 22nd ed.; supplemented by EyeWorld and PMID PMC10726981 (phakic IOLs vs. excimer laser for high myopia - systematic review showing superior safety with phakic IOLs).

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