SMILE Eye Surgery: Suitability, Procedure, Risks and Recovery

Author: Dr Val Phua
Estimated reading time: 21 minutes

SMILE is a laser vision-correction procedure used to reduce dependence on spectacles or contact lenses.

The name stands for small-incision lenticule extraction.

During SMILE, a femtosecond laser creates a thin, lens-shaped piece of tissue—called a lenticule—within the cornea. The surgeon separates and removes this lenticule through a small corneal opening.

Removing the lenticule changes the curvature and focusing power of the cornea.

SMILE is primarily used to correct:

Myopia, or short-sightedness
Myopic astigmatism

SMILE is commonly described as a “flapless” procedure. More precisely, it does not create the large hinged corneal flap used in LASIK. It still creates a small incision and an internal interface within the cornea.

Potential advantages include:

No LASIK flap
A small corneal incision
Less disruption of some anterior corneal nerves
Potentially fewer early dry-eye effects than LASIK
No risk of later traumatic displacement of a LASIK flap
Good refractive stability
Suitability for many active patients

However, SMILE is not automatically safer or more appropriate for every eye.

Possible limitations include:

Slightly slower early visual sharpening than LASIK
More limited customisation on some laser platforms
More complicated enhancement options
Dependence on technically successful lenticule separation and removal
Residual refractive error
Glare, halos or night-vision symptoms
Dry eye
Inflammation or infection
Rare corneal ectasia
Rare loss of corrected vision

Randomised trials and systematic reviews generally find that SMILE and femtosecond LASIK provide comparable overall safety and efficacy for appropriately selected patients with myopia and myopic astigmatism. LASIK may be slightly more predictable in some analyses, while SMILE may induce less spherical aberration and have a smaller early effect on the ocular surface.

The Quick Answer

What Is SMILE?

SMILE is a laser refractive procedure in which a femtosecond laser creates a precisely shaped lenticule within the corneal stroma.

The surgeon removes the lenticule through a small incision, usually without creating a LASIK-style flap.

What Does SMILE Treat?

SMILE is most established for:

Myopia
Myopic astigmatism

The treatable range depends on:

The laser platform
Local regulatory approval
Corneal thickness
Corneal shape
Prescription
Optical-zone requirements
Tissue calculations
The surgeon’s clinical assessment

Although hyperopic lenticule extraction is being investigated and has produced encouraging early results, myopic SMILE remains the most established application.

Is SMILE Painful?

Most patients feel little or no pain during the procedure.

Anaesthetic eye drops numb the cornea.

Patients may notice:

Pressure around the eye
Temporary dimming or loss of the fixation light
Bright or blurred lights
Awareness of the surgeon touching the eye
Mild pulling or movement during lenticule removal

Sharp pain is not expected.

How Long Does SMILE Take?

The entire procedure commonly takes approximately 10 to 20 minutes for both eyes.

The femtosecond-laser treatment itself usually takes only a short time.

Additional time is required for:

Eye alignment
Suction
Laser treatment
Lenticule separation
Lenticule removal
Final examination

How Quickly Does Vision Recover?

Many patients have functional vision by the following day.

Vision may continue improving over:

Several days
Several weeks
Occasionally several months

Compared with LASIK, visual acuity may be similar early after surgery, but contrast and subjective visual sharpness can recover slightly more slowly during the first week. These differences commonly diminish by one month.

Is SMILE Permanent?

The removed corneal tissue does not grow back in its original form.

However, the eye can still change because of:

Continuing myopic progression
Age-related refractive change
Presbyopia
Cataract formation
Corneal remodelling
Diabetes-related refractive fluctuation

Ten-year studies show that SMILE can remain effective and stable, although small degrees of regression may occur over time.

Will I Never Need Spectacles Again?

Not necessarily.

Spectacles may still be helpful for:

Very fine distance vision
Night driving
Reading after presbyopia develops
Small residual refractive errors
Prolonged computer work
Future cataract-related changes

The realistic objective is to reduce dependence on spectacles or contact lenses—not to guarantee lifelong spectacle independence.

Understanding How SMILE Corrects Vision

Myopia

Myopia occurs when light focuses in front of the retina rather than directly on it.

Patients with myopia generally see nearby objects more clearly than distant objects.

In myopic SMILE, removing a central stromal lenticule flattens the cornea and reduces its focusing power.

Astigmatism

Astigmatism occurs when the eye has different focusing power in different meridians.

The lenticule is shaped asymmetrically to correct the cylindrical component of the prescription.

Accurate correction depends on:

Reliable refraction
Correct treatment axis
Eye alignment
Centration
Cyclotorsion management
Corneal shape
Lenticule removal without distortion

Systematic reviews indicate that SMILE and LASIK provide broadly comparable astigmatic results. However, uncorrected cyclotorsion can reduce astigmatic accuracy, particularly in eyes with higher cylinder. Cyclotorsion-compensation strategies may improve outcomes.

What Is a Lenticule?

A lenticule is a precisely shaped disc of corneal stromal tissue.

Its:

Diameter
Thickness
Shape
Position
Astigmatic profile

are determined by the planned refractive correction.

Higher myopic corrections generally require a thicker central lenticule.

What Happens to the Cornea After Removal?

Once the lenticule has been removed:

The front layers of the cornea settle.
The central corneal curvature becomes flatter.
The focusing power decreases.
Distant light is focused closer to the retina.

The cornea then undergoes healing and remodelling over the following weeks and months.

Is SMILE Really Flapless?

SMILE is frequently described as flapless because it does not create a large hinged corneal flap.

However, it still creates:

A thin anterior stromal cap
An internal lenticule
A stromal interface
A small access incision

The distinction matters because SMILE avoids flap displacement and some flap-specific problems, but it is not a surface-only or incision-free treatment.

Who May Be Suitable for SMILE?

A suitable candidate generally has:

Myopia or myopic astigmatism within an appropriate range
A stable prescription
Healthy corneal shape
Adequate corneal thickness
No keratoconus or ectasia
A reasonably healthy ocular surface
No visually significant cataract
No uncontrolled eye disease
Realistic expectations
The ability to cooperate during laser docking and lenticule removal

Recent Asia-Pacific consensus guidance emphasises comprehensive preoperative assessment, stable refraction, corneal imaging, careful treatment planning and structured postoperative care.

How Stable Must the Prescription Be?

The prescription should generally remain stable for at least approximately one year.

A small change does not always exclude treatment, but continuing progression means that the refractive result may not remain accurate.

Instability is more likely in:

Younger patients
Progressive myopia
Pregnancy
Breastfeeding
Poorly controlled diabetes
Hormonal change
Certain medication use
Developing cataract

Is There a Minimum Age?

SMILE is generally not performed below 18 years of age.

Reaching 18 does not automatically make a patient suitable.

Many young adults continue to experience myopic progression, particularly when the prescription is high.

Is There a Maximum Age?

There is no universal maximum age.

Older patients require assessment for:

Presbyopia
Early cataract
Dry eye
Glaucoma
Macular degeneration
Corneal endothelial health
Expectations regarding near vision

When early cataract is present, cataract surgery may offer a more appropriate long-term solution.

Who May Not Be Suitable for SMILE?

SMILE may be inappropriate or require particular caution in patients with:

Keratoconus
Suspicious corneal tomography
Corneal ectasia
Inadequate corneal thickness
Unstable refraction
Severe dry eye
Active blepharitis
Recurrent corneal erosion
Epithelial basement membrane dystrophy
Active corneal infection
Previous herpetic keratitis
Uncontrolled glaucoma
Active uveitis
Visually significant cataract
Pregnancy or breastfeeding
Poorly controlled diabetes
Active autoimmune disease
Unrealistic expectations

Abnormal corneal topography and insufficient corneal tissue remain among the most important reasons for excluding patients from corneal refractive surgery.

Pregnancy and Breastfeeding

SMILE is generally postponed during pregnancy and breastfeeding.

Possible concerns include:

Refractive fluctuation
Corneal-curvature change
Dry eye
Hormonal effects on healing
Medication exposure

The prescription and ocular surface should be allowed to stabilise before final measurements are taken.

Diabetes

Well-controlled diabetes does not necessarily exclude every patient.

The assessment should consider:

HbA1c and glucose stability
Diabetic retinopathy
Corneal sensation
Dry eye
Wound healing
Prescription stability
General medical health

Poorly controlled diabetes may produce fluctuating vision and less predictable healing.

Autoimmune Disease

Active autoimmune or connective-tissue disease may increase the risk of:

Dry eye
Delayed healing
Inflammation
Corneal ulceration
Infection
Unpredictable refractive results

Stable disease requires individual assessment and, where appropriate, discussion with the treating physician.

Contact Lenses Before Assessment

Contact lenses can temporarily alter corneal shape.

They should be discontinued before definitive imaging and treatment planning.

The required interval varies according to:

Soft or rigid lenses
Duration of wear
Orthokeratology use
Corneal warpage
Stability of repeat measurements

Rigid gas-permeable and orthokeratology lenses may require a longer period of discontinuation than ordinary soft lenses.

The Pre-SMILE Assessment

The assessment must determine:

Whether the prescription can be corrected accurately
Whether the cornea can be treated safely
Whether SMILE is preferable to LASIK, PRK or ICL
Whether the patient understands the expected benefits and limitations

Medical and Eye History

The surgeon should ask about:

Previous eye surgery
Contact-lens use
Dry eye
Eye rubbing
Allergies
Recurrent corneal erosions
Eye trauma
Herpetic eye disease
Glaucoma
Retinal tears
Diabetes
Autoimmune disease
Pregnancy plans
Medication
Occupational requirements
Contact sports

Visual-Acuity Testing

Unaided and corrected vision are measured.

Corrected vision helps determine the eye’s maximum current visual potential.

SMILE cannot be expected to correct:

Amblyopia
Retinal damage
Optic-nerve disease
Corneal scarring
Other non-refractive causes of poor vision

Manifest Refraction

The subjective spectacle prescription is measured carefully.

This may be repeated because small inaccuracies can affect:

Lenticule shape
Astigmatism treatment
Final refractive result
Binocular balance

Cycloplegic Refraction

Dilating drops temporarily relax accommodation.

This may be useful for:

Younger patients
Suspected accommodative spasm
Inconsistent refraction
Avoiding excessive myopic treatment

Corneal Topography

Topography maps the curvature of the anterior corneal surface.

It helps identify:

Regular astigmatism
Irregular astigmatism
Contact-lens warpage
Decentration
Suspicious keratoconus-like patterns

Corneal Tomography

Tomography analyses the three-dimensional structure of the cornea.

It may assess:

Anterior elevation
Posterior elevation
Corneal thickness
Thickness distribution
Curvature
Ectasia-risk indices
Corneal volume

Normal spectacle-corrected vision does not rule out early keratoconus.

Modern refractive screening increasingly combines tomography with other imaging rather than relying on one measurement alone.

Pachymetry

Pachymetry measures corneal thickness.

The surgeon considers:

Starting thickness
Cap thickness
Lenticule thickness
Residual stromal tissue
Percentage of tissue altered
Corneal shape
Patient age
Degree of myopia

No single thickness number determines suitability in isolation.

Epithelial Thickness Mapping

The epithelium can redistribute itself and partly conceal underlying stromal irregularity.

Epithelial mapping may help identify:

Early ectatic patterns
Contact-lens warpage
Localised epithelial compensation
Irregular corneal shape
Previous corneal treatment

It complements rather than replaces tomography.

Corneal Biomechanical Assessment

Selected clinics use devices that assess the cornea’s response to an air pulse or deformation.

Biomechanical measurements may add information about ectasia susceptibility, but they must be interpreted together with:

Tomography
Topography
Thickness
Age
Prescription
Clinical history

Tear-Film and Dry-Eye Evaluation

The ocular surface should be assessed for:

Tear-film instability
Corneal staining
Conjunctival staining
Meibomian gland dysfunction
Blepharitis
Reduced tear production
Contact-lens-related inflammation

Dry eye can reduce measurement accuracy and cause postoperative fluctuation even when the refractive correction is accurate.

Pupil and Centration Assessment

The surgeon may assess:

Pupil size
Pupil centre
Corneal vertex
Visual axis
Angle kappa
Fixation

Accurate centration is important because decentration can increase:

Coma
Glare
Halos
Ghosting
Reduced visual quality

Eye-Pressure Measurement

Eye pressure is measured to assess glaucoma risk.

After SMILE, conventional pressure measurements may read lower because the cornea has been reshaped.

Future eye-care providers should be informed that corneal refractive surgery has been performed.

Dilated Retinal Examination

The retina and optic nerve may be examined for:

Retinal holes or tears
Lattice degeneration
Myopic macular changes
Glaucoma
Retinal detachment
Other causes of reduced visual potential

Correcting myopia does not remove the retinal risks associated with a long, highly myopic eye.

How Is SMILE Performed?

Step 1: Confirming the Treatment

Before surgery, the team confirms:

Patient identity
Correct eye
Prescription
Astigmatism axis
Laser settings
Corneal measurements
Planned cap and lenticule dimensions

Step 2: Anaesthetic Drops

Anaesthetic drops numb the surface of the eye.

The skin and eyelids are cleaned.

A small instrument keeps the eyelids open.

The patient does not need to worry about blinking.

Step 3: Docking the Eye

The patient looks towards a fixation light.

A curved contact interface approaches the cornea.

Gentle suction stabilises the eye.

The patient may feel pressure, and the fixation light may become blurred or disappear temporarily.

Step 4: Creating the Lenticule

The femtosecond laser creates a series of microscopic bubbles within the corneal stroma.

The laser forms:

The back surface of the lenticule
The lenticule edge
The front surface of the lenticule
A small access incision

The laser does not remove the tissue directly.

It creates tissue-separation planes that allow the surgeon to extract the lenticule.

Step 5: Releasing Suction

After the laser treatment is complete, the suction is released.

The surgeon then performs the manual part of the procedure.

Step 6: Identifying the Tissue Planes

A fine instrument is passed through the small incision.

The surgeon identifies:

The plane above the lenticule
The plane below the lenticule

Correct identification of these planes is essential.

Step 7: Separating the Lenticule

The lenticule is gently separated from the surrounding corneal tissue.

The surgeon moves around its circumference to ensure that it is fully mobile.

Step 8: Removing the Lenticule

The lenticule is grasped and removed through the small incision.

The surgeon inspects it to confirm that it is complete.

Step 9: Checking the Interface

The cornea is examined for:

Retained tissue
Interface debris
Centration
Smoothness
Incision integrity
Excessive inflammation

No stitches are usually required.

Can Both Eyes Be Treated Together?

Yes.

Bilateral same-day SMILE is common.

Advantages include:

Simultaneous recovery
Reduced binocular imbalance
One main postoperative period
Fewer separate procedure visits

Each eye still requires independent planning and safety checks.

What Does the Patient Experience?

During laser docking, the patient may notice:

Pressure
A bright fixation light
The light becoming blurred
Temporary dimming of vision
A grey or dark view

During lenticule separation, the patient may notice movement or pressure but should not feel sharp pain.

A randomised paired-eye study found that both SMILE and LASIK were generally well tolerated, although the subjective experience differed between the procedures.

What Happens Immediately After SMILE?

Temporary symptoms may include:

Hazy vision
Watering
Grittiness
Light sensitivity
Mild burning
Halos
Fluctuating focus

Discomfort is usually mild.

Patients should avoid rubbing or squeezing the eyes.

Eye Drops After SMILE

Postoperative medication commonly includes:

Antibiotic drops
Steroid drops
Preservative-free lubricants

The exact regimen varies.

Patients should:

Wash their hands
Avoid touching the bottle tip to the eye
Use drops according to schedule
Space different medications apart
Avoid stopping steroid drops without advice

The First Night

Protective shields may be recommended during sleep.

The patient should avoid:

Eye rubbing
Pressing on the eyelids
Sleeping face-down
Allowing accidental contact from children or pets

The First Day

Many patients can see well enough for ordinary indoor activities.

Vision may still feel:

Slightly misty
Less crisp than expected
Variable between blinks
More affected in dim lighting

A postoperative examination checks:

Vision
Corneal surface
Incision
Interface
Inflammation
Evidence of infection

The First Week

Visual acuity often improves quickly, but fine sharpness and contrast may continue improving.

Compared with LASIK, some patients experience a slightly slower recovery of contrast and subjective optical clarity during the first week, although overall satisfaction is usually similar.

The First Month

By one month, many patients have stable functional vision.

Temporary symptoms may still include:

Dryness
Glare
Halos
Mild fluctuation
Reduced clarity at night

Three to Six Months

The corneal nerves, tear film and optical system continue adapting.

Small refractive or visual-quality changes may continue during this period.

Expected Visual Results

SMILE generally provides high rates of useful unaided distance vision in appropriately selected patients.

A one-year study of 405 eyes found that 79% achieved 20/20 or better unaided vision and 99% achieved at least 20/40. Eighty-four per cent were within 0.50 dioptres of the intended spherical-equivalent target and 97% were within 1.00 dioptre. Outcomes vary according to the treatment range, platform, surgeon and study population.

Studies of high myopia have also shown good safety and patient satisfaction, although predictability generally becomes more challenging as the prescription increases.

Long-Term Stability

Two published ten-year studies found that SMILE remained effective and generally stable over a decade.

One study reported approximately 81% of eyes within 0.50 dioptres and 94% within 1.00 dioptre of target at ten years, with an average regression of approximately 0.32 dioptres. Another early cohort found no significant deterioration from its six-month result and no reported late ectasia or persistent dry eye within the followed group. These studies are encouraging but involved relatively small numbers of patients.

Is 20/20 the Same as Perfect Vision?

No.

A standard visual-acuity chart does not fully measure:

Contrast sensitivity
Night vision
Glare
Halos
Starbursts
Ghost images
Tear-film fluctuation
Visual comfort

A patient may read 20/20 while still noticing optical symptoms.

Visual Quality After SMILE

SMILE changes the shape and higher-order optics of the cornea.

Possible postoperative effects include increases in:

Coma
Spherical aberration
Trefoil
Total higher-order aberrations

The amount depends on:

Correction magnitude
Optical-zone size
Centration
Healing
Lenticule regularity
Pupil size

A 2024 systematic review confirmed that higher-order aberrations can increase after SMILE, particularly coma and spherical aberration, although results vary between studies and measurement conditions.

Effective Optical Zone

The effective optical zone is the part of the treated cornea that provides the intended correction.

It may be smaller than the programmed optical zone because of:

Corneal biomechanics
Epithelial remodelling
Treatment magnitude
Transition-zone design
Measurement method

A smaller effective optical zone may contribute to night-vision symptoms, particularly with large pupils or high myopic corrections.

Glare, Halos and Starbursts

Possible night-time symptoms include:

Rings around lights
Star-shaped rays
Headlight glare
Ghost images
Reduced contrast
Smearing

These may be related to:

Dry eye
Residual refractive error
Higher-order aberrations
Decentration
Large pupils
Optical-zone limitations

Symptoms often improve as the tear film and cornea stabilise.

Dry Eye After SMILE

SMILE can still cause dry eye.

The procedure alters:

Corneal nerves
Corneal sensation
Reflex tearing
Blinking
Tear-film regulation

Possible symptoms include:

Burning
Grittiness
Fluctuating vision
Tired eyes
Redness
Light sensitivity
Excessive tearing

Is Dry Eye Less Common Than After LASIK?

On average, SMILE appears to have a smaller early effect on corneal sensation and several dry-eye measures than femtosecond LASIK.

This is thought to relate to the smaller incision and reduced disruption of the anterior stromal nerve plexus.

A recent systematic review and meta-analysis found better tear-film stability and corneal-sensitivity preservation after lenticule extraction than after femtosecond LASIK. Earlier meta-analysis reached a similar conclusion. However, individual patients can still develop significant or persistent symptoms.

Treating Dry Eye

Management may include:

Preservative-free artificial tears
Lubricating gel
Warm compresses
Lid hygiene
Treatment of meibomian gland dysfunction
Anti-inflammatory eye drops
Punctal plugs
Autologous serum
Scleral lenses in severe cases

Pre-existing ocular-surface disease should be treated before surgery.

Regression

Regression means that part of the original myopia returns after treatment.

Possible contributors include:

High preoperative myopia
Corneal healing
Epithelial remodelling
Continuing axial elongation
Age-related lens changes
Residual astigmatism

A small degree of long-term regression has been documented in ten-year studies.

Residual Refractive Error

The achieved prescription may differ from the target.

Possible causes include:

Measurement variation
Biological healing
Centration
Astigmatic-axis error
Lenticule irregularity
High correction
Tear-film instability
Cyclotorsion
Continuing myopia

A small residual prescription may be managed with spectacles or contact lenses.

Enhancements After SMILE

Enhancement options are more complex than simply relifting a recent LASIK flap.

Possible approaches include:

PRK or TransPRK over the SMILE cap
Conversion of the cap into a LASIK-style flap
Thin-flap LASIK
Repeat lenticule extraction in selected settings
Spectacles or contact lenses
ICL in selected high residual errors

A review of enhancement techniques found that surface ablation, cap-to-flap conversion and thin-flap LASIK can all be effective when appropriately selected. The choice depends on residual error, corneal thickness, interface anatomy and surgeon experience.

When Is an Enhancement Considered?

An enhancement may be considered when:

A meaningful residual prescription remains
The result has stabilised
Dry eye has been treated
The cornea remains structurally suitable
The visual limitation is explained by the refractive error
The expected benefit exceeds the additional risk

Not every small residual error requires another operation.

Intraoperative Risks and Difficulties

Suction Loss

Suction may be lost if:

The eye moves significantly
The patient squeezes the eyelids
Excess fluid enters the docking interface
The docking is unstable
The suction system disengages

The appropriate response depends on which laser cut has been completed.

The procedure may be:

Restarted
Re-docked
Converted to another treatment
Postponed

Studies show that successful immediate reapplication can produce outcomes similar to uncomplicated SMILE when handled appropriately.

Difficult Lenticule Separation

The tissue planes may be more difficult to identify when there is:

Incomplete laser separation
An opaque bubble layer
Black spots
Interface fluid
Low correction with a thin lenticule
Surgical learning-curve factors

Careful dissection is required to avoid tearing the lenticule or cap.

Retained Lenticule Tissue

A small fragment may remain within the interface if the lenticule is incomplete or torn.

This may cause:

Residual myopia
Irregular astigmatism
Reduced vision
Interface inflammation

The fragment may need to be removed.

Cap Perforation or Tear

The thin anterior cap may be perforated during dissection.

Small peripheral defects may heal without significant effect.

Larger or central damage may cause:

Irregular astigmatism
Scarring
Delayed recovery
Reduced visual quality

Incision Damage

The small access incision may become:

Torn
Enlarged
Irregular
Epithelialised

Careful instrument handling reduces this risk.

Decentration

The lenticule may be created away from the ideal treatment centre.

Decentration can contribute to:

Coma
Ghosting
Glare
Reduced optical quality
Residual refractive error

Modern planning, patient fixation and platform-specific centration systems help reduce the risk.

Reviews of SMILE complications emphasise that many intraoperative problems are manageable but require correct recognition and technique.

Postoperative Complications

Interface Inflammation

Inflammatory cells may accumulate within the stromal interface.

This may resemble diffuse lamellar keratitis after LASIK.

Symptoms may include:

Haze
Blurred vision
Light sensitivity
Discomfort

Treatment often involves steroid eye drops.

More severe inflammation may require intensive treatment or interface irrigation.

Diffuse Lamellar Keratitis

Diffuse lamellar keratitis, or DLK, is a sterile inflammatory reaction within the corneal interface.

It may appear as fine white granular cells.

Prompt recognition is important because severe inflammation can affect the central cornea and reduce vision.

A long-term series of 6,373 SMILE cases reported DLK in approximately 2.2% of treated eyes, although rates vary by centre, diagnostic threshold and surgical protocol.

Central Toxic Keratopathy

Central toxic keratopathy is a rare, non-infectious condition characterised by:

Central stromal haze
Corneal flattening
Hyperopic shift
Tissue loss or striae

It must be distinguished from DLK because management differs.

Contemporary reviews describe DLK, central toxic keratopathy and transient light-sensitivity syndrome as separate uncommon inflammatory or toxic conditions after lamellar refractive surgery.

Infection

Infectious keratitis after SMILE is rare but potentially sight-threatening.

Infection may occur within the relatively deep stromal interface, making diagnosis and drug delivery more challenging.

Warning signs include:

Increasing pain
Increasing redness
Worsening vision
Marked light sensitivity
Discharge
A white corneal spot

Urgent treatment may include:

Intensive antimicrobial drops
Opening and irrigating the interface
Microbiological sampling
Systemic medication in selected infections

A 2025 review emphasised that prompt recognition is essential because interface infections after lenticule extraction may be more difficult to access than surface infections.

Epithelial Ingrowth

Surface epithelial cells may grow into the incision or interface.

Small areas may remain stable.

Progressive ingrowth may cause:

Irregular astigmatism
Inflammation
Reduced vision
Stromal melting
Interface haze

Treatment may require opening and cleaning the interface.

Interface Debris

Small particles may be trapped within the interface.

These may include:

Fibres
Meibomian material
Metallic particles
Surgical debris

Most peripheral debris causes no meaningful symptoms.

Central or inflammatory material may require treatment.

Corneal Haze

Mild interface haze may temporarily reduce visual quality.

Persistent haze requires assessment for:

Inflammation
Infection
Irregular healing
Retained material
Central toxic keratopathy

Corneal Ectasia

Corneal ectasia is progressive thinning and bulging of the cornea.

It may cause:

Increasing myopia
Increasing astigmatism
Ghosting
Reduced corrected vision
Irregular tomography
Contact-lens dependence

SMILE may preserve more of the anterior corneal structure than LASIK, but it does not eliminate ectasia risk.

A systematic review found reported ectasia after SMILE to be rare. Many published cases occurred in eyes with pre-existing suspicious topography or subclinical keratoconus.

Treatment may include:

Corneal cross-linking
Spectacles
Rigid contact lenses
Scleral lenses
Intracorneal ring segments
Specialised surface treatment
Corneal transplantation in advanced cases

Is SMILE Xtra Safer for Borderline Corneas?

SMILE Xtra combines SMILE with prophylactic corneal cross-linking.

It has been proposed for eyes considered at greater biomechanical risk.

Published cohort studies report encouraging short-term results, but they do not establish that borderline or suspicious corneas should automatically undergo refractive surgery.

Cross-linking does not make an unsuitable keratoconic cornea suitable.

Long-term comparative evidence remains limited.

Loss of Corrected Vision

Rarely, an eye may not see as clearly with spectacles after surgery as it did beforehand.

Possible causes include:

Irregular astigmatism
Infection
Scarring
Ectasia
Decentration
Retained lenticule tissue
Severe inflammation
Ocular-surface disease

Large studies indicate that loss of two or more lines of corrected distance vision is uncommon, but it cannot be reduced to zero.

SMILE Versus LASIK

Both procedures can produce excellent outcomes for myopia and myopic astigmatism.

Possible Advantages of SMILE

No hinged flap
Smaller incision
Lower risk of traumatic flap displacement
Better early preservation of corneal sensation
Potentially fewer early dry-eye effects
Possibly less induction of spherical aberration
Potential biomechanical advantages

Possible Advantages of LASIK

Faster early optical recovery
Wider availability of wavefront- and topography-guided profiles
Active eye tracking on established platforms
Straightforward cyclotorsion compensation
Easier enhancement by flap relifting
Broader established use for hyperopia
Immediate access to the stromal treatment bed

Meta-analysis of randomised trials found similar safety, efficacy and final unaided vision. LASIK was slightly more likely to achieve refraction within 0.50 dioptres in one analysis, while SMILE induced less spherical aberration.

SMILE Versus PRK

PRK removes the corneal epithelium and applies an excimer laser directly to the anterior stroma.

Possible Advantages of SMILE

Less early discomfort
Faster epithelial recovery
Lower risk of surface haze
Faster return to daily activities
No large epithelial defect

Possible Advantages of PRK

No flap or stromal cap
More established topography-guided customisation
May preserve more deep stromal tissue in selected treatment plans
Easier surface enhancement pathway
May suit certain thin or irregular-but-non-ectatic corneas

Limitations of PRK

More early pain
Slower recovery
Longer steroid course
Risk of haze
Greater early visual fluctuation

The best choice depends on corneal structure, prescription, occupation and visual priorities.

SMILE Versus ICL

An implantable collamer lens is placed inside the eye without removing the natural lens.

Possible Advantages of SMILE

No intraocular implant
No intraocular surgery
No ICL vault or sizing concerns
No ICL-related cataract or pressure risk
Rapid recovery

Possible Advantages of ICL

No corneal stromal tissue removal
Suitable for higher prescriptions
Often excellent optical quality
Removable or exchangeable
Useful when the cornea is unsuitable for laser correction

In a comparative study of high myopia, both ICL and SMILE produced high satisfaction. ICL induced fewer higher-order aberrations, while halos were more frequently reported after ICL.

Is SMILE Better for High Myopia?

SMILE can treat selected high-myopic eyes, and published studies report good outcomes.

However, higher myopia requires:

A thicker lenticule
Greater tissue alteration
Careful residual-tissue calculations
Larger attention to optical-zone effects
More counselling about regression
Retinal assessment

An ICL may be more appropriate when:

The prescription is very high
The cornea is thin
The projected tissue removal is excessive
Optical quality is a major priority
The eye is otherwise suitable for an intraocular lens

The choice should be based on safety and long-term suitability, not merely whether the laser can technically enter the prescription.

SMILE and Presbyopia

Standard SMILE corrects distance refractive error but does not restore the natural lens’s ability to focus at near.

Patients approaching their forties should expect presbyopia to develop.

Possible strategies include:

Both eyes corrected for distance with reading glasses
Monovision
Mini-monovision
Leaving mild myopia intentionally
Considering another refractive option

A contact-lens monovision trial may help determine whether the patient can adapt.

SMILE and Hyperopia

Hyperopic SMILE or lenticule extraction is under active investigation.

The treatment requires removal of a ring-shaped or differently profiled lenticule to steepen the central cornea.

Early multicentre research has reported promising refractive results, but hyperopic SMILE is less established than myopic SMILE and may not be available or approved in every region.

Can SMILE Treat Presbyopia Directly?

Specialised lenticule-extraction approaches for presbyopia are being investigated.

They should not be regarded as equivalent to standard myopic SMILE.

Patients should understand:

The optical trade-offs
The possibility of halos
The effect on contrast
The eventual development of cataract
The limits of current long-term evidence

SMILE for Athletes

SMILE may appeal to patients participating in:

Martial arts
Rugby
Football
Racquet sports
Military activity
Outdoor sports

There is no large hinged flap that can be displaced later by trauma.

However, the eye can still suffer:

Corneal injury
Retinal injury
Infection
Blunt trauma

Protective eyewear remains important.

When Can I Exercise?

Gentle walking is usually possible early.

Strenuous exercise may be restricted temporarily.

The patient should avoid:

Sweat entering the eyes
Eye rubbing
Dirty environments
Activities with a risk of facial impact

When Can I Swim?

Swimming is generally avoided during the early healing period.

Pool, sea and spa water may contain organisms or irritants.

The surgeon should provide a specific timeline.

When Can I Use Screens?

Screens do not damage the cornea or reverse SMILE.

However, prolonged screen use reduces blinking and may worsen:

Dryness
Burning
Fluctuating vision
Eye fatigue

Regular breaks and lubricating drops may help.

When Can I Drive?

Driving should resume only when:

Vision meets the legal standard
The patient feels confident
Glare is manageable
Depth perception is comfortable
The surgeon has not advised otherwise

The patient should not drive home immediately after surgery.

Can I Fly?

Uncomplicated SMILE does not place gas inside the eye and usually does not prevent flying.

Aircraft cabins may worsen dryness.

Travel should not interfere with postoperative examinations.

Cataract Surgery After SMILE

Patients who undergo SMILE may still develop cataracts later.

Previous SMILE alters corneal curvature and can make intraocular lens power calculation more challenging.

Patients should retain:

Preoperative refraction
Corneal measurements
Operative reports
Treatment details

Modern post-refractive formulas and total-corneal measurements can improve cataract-lens calculations, but refractive prediction remains less straightforward than in an untreated cornea.

Glaucoma Assessment After SMILE

Conventional eye-pressure measurements may underestimate pressure after corneal refractive surgery.

Patients should inform future eye-care providers that SMILE has been performed.

Glaucoma assessment should also consider:

Optic-nerve appearance
OCT nerve-fibre measurements
Visual fields
Corneal thickness
Alternative pressure-measurement methods

Retinal Risk After SMILE

SMILE corrects the cornea but does not shorten the eyeball.

A highly myopic patient may remain at increased risk of:

Retinal tears
Retinal detachment
Myopic macular degeneration
Macular schisis
Glaucoma

Urgent assessment is required for:

New flashes
A sudden increase in floaters
A curtain or shadow
Sudden visual loss

Common Myths

“SMILE Is Completely Incision-Free”

False.

It uses a small incision to remove the lenticule.

“SMILE Has No Corneal Interface”

False.

An internal stromal interface remains after the lenticule is removed.

“SMILE Cannot Cause Dry Eye”

False.

Dry eye can occur, although average early ocular-surface effects may be less than after LASIK.

“SMILE Cannot Cause Ectasia”

False.

The risk appears low but is not zero.

Keratoconus and suspicious tomography remain important contraindications.

“SMILE Is Always Better Than LASIK”

False.

Both procedures have advantages and limitations.

The best choice depends on the individual eye.

“SMILE Is Always Better for Thin Corneas”

False.

A thin cornea requires full structural analysis.

SMILE also removes stromal tissue and may be inappropriate.

“There Is No Risk of Inflammation Because There Is No Flap”

False.

Interface inflammation, including DLK, can occur after SMILE.

“Enhancement Is Impossible After SMILE”

False.

Enhancement is possible, but the options are more complex than simple LASIK flap relifting.

“SMILE Prevents Presbyopia”

False.

The natural lens continues ageing.

“Correcting High Myopia Removes the Retinal Risk”

False.

The eye remains anatomically myopic even when distance vision no longer requires spectacles.

Frequently Asked Questions

Am I Too Short-Sighted for SMILE?

Suitability depends on:

Corneal thickness
Corneal shape
Treatment range
Lenticule thickness
Residual tissue
Optical-zone requirements
Retinal health
Alternative options such as ICL

Can SMILE Correct Astigmatism?

Yes, selected myopic astigmatism can be treated.

Higher astigmatism may require particular attention to axis alignment and cyclotorsion.

Is SMILE More Accurate Than LASIK?

Overall outcomes are comparable.

Some analyses find slightly greater predictability with LASIK, while SMILE may induce less spherical aberration and fewer early dry-eye effects.

Does the Surgeon Pull Tissue Out of the Eye?

Yes.

The femtosecond laser creates the lenticule, but the surgeon manually separates and removes it through the small incision.

What Happens if the Lenticule Tears?

The surgeon attempts to identify and remove all remaining tissue.

A retained fragment may require further removal.

What Happens if Suction Is Lost?

The management depends on when the suction loss occurs.

The laser may be restarted, re-docked, converted or postponed.

Can I Blink During the Procedure?

An eyelid holder prevents blinking during the important steps.

What Happens if I Move My Eye?

Suction stabilises the eye during laser delivery.

The patient should still follow fixation instructions.

Can SMILE Be Reversed?

No.

The removed stromal tissue cannot simply be replaced in routine clinical practice.

Experimental research has investigated lenticule preservation and reuse, but this is not equivalent to routine reversal.

Can I Have SMILE Again?

Repeat lenticule extraction is possible only in selected circumstances and is not the usual enhancement strategy.

PRK or cap-to-flap conversion is more commonly considered.

Will I Need Reading Glasses?

Patients approaching presbyopic age should expect to need near correction unless monovision is selected.

Even with monovision, spectacles may be useful for fine or prolonged reading.

Can Both Eyes Be Treated on the Same Day?

Yes.

This is common when both eyes are suitable.

Can SMILE Cause Blindness?

Severe permanent visual loss is very rare.

Potential causes include:

Infection
Severe ectasia
Corneal scarring
Uncontrolled inflammation
Other unrelated eye disease

The risk is small but not zero.

Is SMILE Suitable After LASIK?

Usually not as a straightforward standard procedure because the previous LASIK flap and stromal anatomy alter the treatment planes.

Other enhancement methods may be more appropriate.

Can I Wear Contact Lenses Again?

Yes, if needed.

Some patients may require contact lenses for:

Residual refractive error
Irregular astigmatism
Ectasia
Special visual tasks

Does SMILE Change Eye Colour?

No.

The iris is not treated.

Can I Rub My Eyes After SMILE?

Eye rubbing should be avoided during healing.

Long-term vigorous rubbing is also discouraged because it can:

Irritate the ocular surface
Worsen allergy
Stress the cornea
Contribute to ectatic change in susceptible eyes

Is SMILE Suitable for Contact-Sport Athletes?

It may be particularly attractive because there is no large LASIK flap.

However, individual corneal suitability and protection against future eye trauma remain essential.

When to Seek Urgent Eye Care

Seek urgent assessment for:

Increasing pain
Increasing redness
Rapidly worsening vision
Marked light sensitivity
Thick discharge
A white corneal spot
Vision worsening after initial improvement
Significant eye trauma
New flashes or floaters
A curtain or shadow
Severe or persistent headache with eye symptoms

Severe pain or worsening vision should not be assumed to be ordinary dryness.

A SMILE Assessment Checklist

Visual Goals to Discuss

Distance vision
Near vision
Computer use
Night driving
Sports
Occupation
Spectacle independence
Monovision
Tolerance of glare or halos

Medical Information to Report

Diabetes
Autoimmune disease
Thyroid disease
Pregnancy or breastfeeding
Allergies
Migraine
Chronic pain
Medication
Previous healing problems

Eye History to Report

Dry eye
Contact-lens intolerance
Eye rubbing
Keratoconus in the family
Recurrent corneal erosion
Herpetic keratitis
Glaucoma
Retinal tear or detachment
Eye trauma
Previous eye surgery

Tests That May Be Used

Unaided and corrected vision
Manifest refraction
Cycloplegic refraction
Corneal topography
Corneal tomography
Pachymetry
Epithelial mapping
Biomechanical assessment
Tear-film evaluation
Pupil and centration assessment
Eye-pressure measurement
Dilated retinal examination

Questions to Ask the Surgeon

Am I genuinely suitable for SMILE?
Is my corneal tomography completely normal?
Is my prescription stable?
How much stromal tissue will remain?
What is the planned optical-zone size?
Would LASIK, PRK or ICL be safer?
How accurately can my astigmatism be treated?
What is my risk of dry eye?
What is my risk of ectasia?
How quickly should my vision recover?
What happens if suction is lost?
How would residual refractive error be treated?
Which enhancement method would be used?
What warning symptoms require urgent review?
How frequently will I be examined?

The Bottom Line

SMILE is a laser vision-correction procedure that removes a femtosecond-laser-created stromal lenticule through a small corneal incision.

It is primarily used to correct:

Myopia
Myopic astigmatism

Potential advantages include:

No LASIK-style flap
A small incision
Rapid functional recovery
Less early disruption of corneal sensation
Potentially fewer early dry-eye effects
No long-term risk of traumatic LASIK-flap displacement

Possible limitations include:

Slightly slower early visual sharpening than LASIK
More limited customisation on some platforms
More complex enhancement options
Dependence on complete lenticule separation and removal

Possible complications include:

Suction loss
Difficult dissection
Retained lenticule tissue
Cap or incision damage
Interface inflammation
Diffuse lamellar keratitis
Infection
Epithelial ingrowth
Residual refractive error
Regression
Corneal ectasia
Rare loss of corrected vision

SMILE, LASIK and PRK can all produce excellent results in appropriately selected patients.

SMILE may be preferable when avoiding a flap is important or when reduced early ocular-surface disruption is a priority.

LASIK may offer faster initial optical recovery, greater customisation and simpler enhancement.

PRK may be preferable when a surface treatment is considered structurally or occupationally advantageous.

ICL may be more appropriate for high prescriptions or corneas unsuitable for tissue-removing laser surgery.

The most important message is:

SMILE should not be selected merely because it uses a smaller incision. The best procedure is the one that provides the most appropriate balance of corneal safety, refractive accuracy, visual quality and long-term suitability for the individual patient.

References

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