Why Some Patients Should NOT Have LASIK

Author: Dr Val Phua
Estimated reading time: 17 minutes

LASIK is a well-established form of laser vision correction that can provide excellent vision and rapid recovery in appropriately selected patients.

However, LASIK is elective surgery performed on an otherwise healthy cornea. The aim should not simply be to determine whether a prescription can technically be treated. The more important question is whether LASIK provides a sufficiently wide safety margin for that particular eye.

Some patients should not undergo LASIK because the procedure could:

Weaken an already vulnerable cornea
Worsen severe dry-eye disease
Produce an unpredictable refractive result
Interfere with future glaucoma monitoring
Fail to treat the true cause of blurred vision
Create unnecessary flap-related risk
Provide less benefit than another form of vision correction

Other patients may not be suitable at present but could reconsider surgery after their prescription, pregnancy, eye surface or medical condition has stabilised.

Contraindications are not always identical across every laser platform or country. Current professional reviews distinguish between absolute contraindications—where corneal laser surgery should generally not be performed—and relative contraindications that require individual assessment. Absolute concerns include unstable refraction, keratoconus, poorly controlled dry eye, active autoimmune disease and poorly controlled diabetes. Pregnancy, glaucoma history, previous uveitis and selected medications are commonly treated as relative or temporary contraindications.

LASIK Is Not the Best Procedure for Everyone

A patient should not choose LASIK simply because:

It is widely advertised
A friend had a good result
It has a fast recovery
The spectacle prescription falls within a laser’s treatment range
An initial screening machine says the cornea is thick enough
It is the only refractive procedure offered by a particular clinic

LASIK creates a permanent corneal flap and permanently removes stromal tissue. The removed tissue cannot be replaced, and the cornea cannot be returned completely to its original structure.

A careful decision must consider:

Prescription stability
Corneal topography and tomography
Corneal thickness
Expected tissue removal
Residual stromal-bed thickness
Epithelial thickness distribution
Dry-eye and eyelid health
Pupil size
Eye pressure and optic nerve health
Natural-lens clarity
Retinal health
General health
Occupation and lifestyle
Expectations regarding glasses and visual quality

The safest recommendation may be LASIK, SMILE, PRK, an Implantable Collamer Lens, cataract surgery, spectacles, contact lenses—or no operation.

Three Different Reasons Not to Have LASIK

It is useful to divide patients into three groups.

Patients Who Should Generally Not Have LASIK

These may include patients with:

Keratoconus or another corneal ectatic disorder
An unstable prescription
Insufficient corneal tissue
Severe, poorly controlled dry-eye disease
Active eye infection or inflammation
Active autoimmune disease affecting healing
Poorly controlled diabetes
Significant cataract causing the visual symptoms
Unrealistic expectations that surgery cannot meet

Patients Who Should Postpone LASIK

These may include patients who are:

Pregnant
Breastfeeding
Still experiencing myopia progression
Recovering from an eye infection or inflammation
Undergoing treatment for dry eye, blepharitis or allergy
Taking medication that temporarily affects refraction or healing
Waiting for contact lens-induced corneal distortion to resolve
Experiencing unstable diabetes-related vision

Patients Who Require Individual Specialist Assessment

These may include patients with:

Controlled glaucoma or ocular hypertension
Controlled diabetes
Stable autoimmune disease
A previous ocular herpes infection
Previous corneal or refractive surgery
A family history of keratoconus
Borderline corneal measurements
High myopia
Large pupils
Amblyopia or strabismus
Previous retinal surgery
A high risk of direct eye trauma

A relative contraindication does not necessarily mean that surgery is impossible. It means the balance between benefit and risk requires greater caution.

Patients With an Unstable Prescription Should Not Have LASIK Yet

LASIK corrects the prescription measured at the time of surgery. It does not stop the eye from continuing to grow or change.

A patient whose myopia is still progressing may initially see well after surgery but later become short-sighted again.

Possible consequences include:

Renewed dependence on spectacles
Reduced satisfaction
A request for enhancement
Further removal of corneal tissue
Inability to undergo enhancement because insufficient tissue remains

Many current laser indications define refractive stability as no more than approximately 0.50 dioptres of change over the preceding year, although the exact criterion varies by platform and jurisdiction.

Who Is More Likely to Have an Unstable Prescription?

This includes some patients who are:

In their late teens or early twenties
Experiencing continuing myopia progression
Pregnant or breastfeeding
Poorly controlled diabetic
Developing cataract
Taking medication that affects vision
Wearing contact lenses that distort the corneal shape
Experiencing severe tear-film instability

The FDA specifically identifies recent changes in spectacle or contact lens prescription, young age, pregnancy, breastfeeding, diabetes-related hormonal changes and vision-altering medication as reasons for concern about refractive instability.

Patients Under 18 Should Not Have Routine LASIK

LASIK is generally not performed in children because:

The eye is still developing
Myopia may continue to progress
The long-term refractive result is less predictable
The patient may not fully understand the permanent nature of surgery

The FDA states that no lasers are approved for LASIK in people below 18 years of age. Some individual platforms have higher minimum ages, such as 21 or 22 years.

Reaching the minimum age does not automatically establish suitability. An 18- or 21-year-old whose prescription is still increasing should usually wait until stability is demonstrated.

Pregnant or Breastfeeding Patients Should Postpone LASIK

Pregnancy and breastfeeding can temporarily change:

Corneal thickness
Corneal curvature
Tear production
Contact lens tolerance
Refraction
Hormonal and fluid balance

The prescription measured during this period may not represent the patient’s long-term refractive state.

Published reviews and current guidance generally recommend postponing LASIK and other corneal refractive procedures during pregnancy. Surgery can be reconsidered after breastfeeding has stopped and the refraction and corneal measurements have stabilised again.

Pregnancy after an uncomplicated LASIK procedure is not automatically dangerous. However, pregnancy-related corneal and refractive changes have been reported, including rare progression of corneal ectasia in susceptible eyes.

Patients With Keratoconus Should Not Have LASIK

Keratoconus is a condition in which the cornea becomes progressively thinner, weaker and more irregular.

LASIK permanently removes corneal tissue and creates a flap. Performing LASIK on a keratoconic or structurally unstable cornea can accelerate weakening and cause postoperative corneal ectasia.

Possible consequences include:

Increasing myopia
Progressive irregular astigmatism
Ghosting or multiple images
Reduced best-corrected vision
Difficulty achieving clear vision with spectacles
Dependence on rigid or scleral contact lenses
Need for corneal cross-linking
Rarely, corneal transplantation

LASIK should generally be avoided in:

Definite keratoconus
Forme-fruste or subclinical keratoconus
Pellucid marginal degeneration
Progressive corneal thinning
Previous corneal ectasia
Strongly suspicious tomography

Keratoconus and abnormal corneal shape are among the most important contraindications to LASIK.

A Normal-Looking Front Corneal Map Is Not Always Enough

Modern assessment should not rely only on the front curvature map.

A structurally vulnerable cornea may show abnormalities in:

Posterior corneal elevation
Thickness distribution
Pachymetric progression
The position of the thinnest point
Epithelial thickness
Corneal biomechanical behaviour
Asymmetry between the two eyes

Post-refractive ectasia is uncommon, but it has been reported after LASIK, PRK and SMILE. A systematic review estimated that reported ectasia in eyes without identifiable preoperative risk factors was more frequent after LASIK than after PRK, although comparisons are limited by differences in patient selection, reporting and procedure volumes.

No scan or formula can guarantee that ectasia will never occur. The purpose of testing is to reduce avoidable risk as much as possible.

Patients With a Family History of Keratoconus Need Extra Caution

A family history does not automatically exclude surgery, but it should increase suspicion.

Additional assessment may include:

Repeat tomography
Epithelial thickness mapping
Corneal biomechanical testing
Comparison between both eyes
Review of older refractions
Assessment for allergy and habitual eye rubbing
A period of observation before deciding

A patient with borderline scans and a strong family history may be better advised to avoid elective corneal tissue removal.

Patients Who Rub Their Eyes Vigorously May Be Poor Candidates

Habitual vigorous eye rubbing is associated with corneal deformation and may contribute to progression in susceptible corneas.

The issue is particularly important in patients with:

Allergic conjunctivitis
Eczema or atopy
Keratoconus risk
Asymmetric corneal shape
Progressive astigmatism
A family history of keratoconus

Allergy should be treated and forceful eye rubbing stopped before elective refractive surgery is considered.

When the patient cannot control habitual rubbing, avoiding LASIK—and sometimes avoiding all corneal laser surgery—may be safer.

Patients With Insufficient Corneal Tissue Should Not Have LASIK

LASIK requires:

Creation of a corneal flap
Removal of stromal tissue beneath the flap

The amount of tissue removed depends on:

The degree of myopia or hyperopia
The amount of astigmatism
Optical-zone diameter
Laser-treatment profile
Flap thickness
Corneal thickness

The flap remains physically present, but most of it does not contribute fully to the load-bearing residual stromal bed.

Important calculations may include:

Expected flap thickness
Expected ablation depth
Residual stromal-bed thickness
Percentage of tissue altered
Total remaining corneal thickness

High percentage of tissue altered, low residual stromal-bed thickness, high myopia and abnormal topography have all been associated with post-LASIK ectasia risk.

There Is No Universal “Safe Corneal Thickness”

A single corneal-thickness number cannot determine safety.

A relatively thick cornea may still be unsafe because of:

Abnormal tomography
Early keratoconus
Unusual epithelial compensation
High planned tissue removal
Significant asymmetry
Poor biomechanical behaviour

A relatively thin cornea may occasionally be suitable for PRK or another approach if its shape is normal and adequate structural tissue remains.

The complete corneal profile matters more than a single central thickness reading.

Patients With Very High Myopia May Be Better Suited to ICL

High myopia is not an automatic contraindication to LASIK, but higher corrections require more tissue removal.

This may increase:

Corneal ectasia concern
Refractive regression
Night-vision symptoms
Higher-order aberrations
Residual prescription
The likelihood that enhancement will be impossible

A patient with a large prescription may obtain a safer structural result with an Implantable Collamer Lens because ICL corrects myopia without removing central corneal tissue.

ICL introduces different risks, including:

Cataract
Raised eye pressure
Incorrect vault
Corneal endothelial cell loss
Inflammation
Infection

The decision should compare the risks of corneal tissue removal with those of an intraocular implant rather than assuming laser surgery is always less invasive.

Patients With Severe Dry Eye Should Not Have LASIK

LASIK temporarily disrupts the corneal nerves involved in:

Tear secretion
Blinking
Corneal sensation
Ocular-surface regulation

Postoperative dry eye may cause:

Burning
Grittiness
Pain
Watering
Light sensitivity
Fluctuating vision
Reduced quality of vision
Contact lens intolerance

Patients with pre-existing dry-eye disease have a greater risk of more severe or persistent symptoms after corneal refractive surgery. LASIK has a particularly strong association with postoperative ocular-surface disturbance because of flap-related corneal denervation.

Dry-Eye Conditions That Should Be Treated Before LASIK

These include:

Meibomian gland dysfunction
Blepharitis
Demodex infestation
Allergic conjunctivitis
Corneal staining
Tear-film instability
Aqueous tear deficiency
Contact lens-related inflammation
Incomplete eyelid closure
Excessive screen-related reduced blinking

Measurements should be repeated after the ocular surface has stabilised because dry eye can affect both refraction and corneal mapping.

When Dry Eye May Rule Out LASIK

LASIK may be inappropriate when there is:

Severe aqueous-deficient dry eye
Sjögren syndrome with ocular-surface disease
Persistent corneal staining despite treatment
Significant corneal sensation loss
Exposure keratopathy
Severe contact lens intolerance caused by dryness
Ocular pain that is disproportionate to visible surface findings
Suspected neuropathic corneal pain
Unstable measurements despite adequate treatment

Chronic dry eye after LASIK is uncommon in some prospective cohorts, but preoperative tear-film and ocular-surface abnormalities help predict who is at greater risk.

Normal Preoperative Tear Symptoms Do Not Eliminate Dry-Eye Risk

A patient who feels comfortable before surgery can still develop dryness afterwards.

In the FDA’s PROWL studies, up to 28% of participants who did not report dry-eye symptoms before LASIK reported symptoms at three months. More than 95% were satisfied with their vision, but the results reinforce the need to discuss side effects rather than presenting LASIK as symptom-free.

Patients With Active Blepharitis or Eye Infection Should Wait

LASIK should not be performed while there is active:

Blepharitis
Bacterial conjunctivitis
Viral conjunctivitis
Corneal infection
Significant allergic inflammation
Keratitis
Uveitis or iritis
Eyelid infection

Active disease may increase the risks of:

Infection
Delayed healing
Inflammation beneath the flap
Corneal scarring
Unstable measurements
Poor visual quality

The FDA specifically identifies blepharitis as a condition that may increase infection or corneal inflammation after LASIK.

Surgery can be reconsidered only after the condition has been adequately treated and the eye has remained stable.

Patients With Significant Cataract Should Not Have LASIK

LASIK reshapes the cornea. It does not remove or treat the natural crystalline lens.

Cataract may cause:

Blurred vision
Glare
Halos
Reduced contrast sensitivity
Difficulty driving at night
Frequent prescription change
Myopic shift
Reduced best-corrected vision

Treating the cornea will not correct blur that is primarily caused by a cloudy natural lens.

In addition, LASIK can make future cataract intraocular-lens calculations more complex. Patients who have previously undergone laser vision correction should retain their old refractive and surgical records for future cataract planning.

When cataract is causing meaningful symptoms, cataract surgery is generally more logical than altering the cornea in front of the cloudy lens.

Patients Over 40 Need Careful Natural-Lens Assessment

Age itself does not rule out LASIK.

However, patients in their forties and fifties may have:

Presbyopia
Early cataract
Natural-lens-related prescription change
Reduced night contrast
A shorter interval before cataract surgery

LASIK does not prevent presbyopia. When both eyes are corrected fully for distance, reading glasses may be needed.

A myopic patient who previously read by removing their glasses may notice a significant reduction in unaided near vision after full distance correction. This is not because LASIK caused presbyopia; it removed the myopia that was providing a near focal point.

Patients with early lens changes may benefit more from continued observation or lens-based surgery than from corneal laser correction.

Patients With Unrealistic Expectations Should Not Proceed

LASIK aims to reduce dependence on spectacles and contact lenses. It does not guarantee:

Perfect vision at every distance
Better visual quality than contact lenses
Permanent spectacle independence
No dry eye
No glare or halos
Perfect night driving
No residual prescription
No future enhancement
No reading glasses
No cataract or glaucoma later in life

A patient who regards any need for glasses as failure may not be psychologically or practically suitable for elective refractive surgery.

The FDA’s PROWL findings showed high overall satisfaction, but up to 46% of participants without preoperative visual symptoms reported at least one visual symptom at three months. Halos were the most frequently reported new symptom. Fewer than 1% reported major difficulty performing usual activities because of any one visual symptom.

This means that most patients do well, but good eye-chart vision does not guarantee perfect subjective visual quality.

Patients With Severe Pre-existing Visual Symptoms Need Careful Counselling

Patients who already experience:

Severe glare
Starbursts
Ghosting
Halos
Poor night driving
Fluctuating vision

should not assume that LASIK will correct these symptoms.

The symptoms may arise from:

Dry eye
Irregular astigmatism
Large pupils
Cataract
Corneal higher-order aberrations
Retinal disease
Migraine
Neurological causes

The underlying cause must be identified before surgery.

Large Pupils Are Not an Automatic Contraindication

Large pupils in dim conditions may increase the risk or awareness of:

Halos
Glare
Starbursts
Ghost images
Reduced night-time contrast

The FDA recommends assessing pupil size in dim lighting and counselling patients about possible night-vision symptoms.

Suitability also depends on:

Optical-zone diameter
Degree of correction
Laser profile
Treatment centration
Pre-existing aberrations
Tear-film stability

A large pupil may be a reason for additional counselling or treatment customisation rather than an automatic reason to refuse surgery.

Patients With Uncontrolled Glaucoma Should Not Have LASIK

LASIK can complicate glaucoma management in several ways.

Eye-Pressure Readings May Become Artificially Lower

LASIK changes:

Corneal thickness
Corneal curvature
Corneal biomechanics

Standard Goldmann applanation tonometry may underestimate eye pressure after surgery. This can make future glaucoma detection or monitoring more difficult.

Steroid Drops Can Raise Eye Pressure

Postoperative steroid medication may cause pressure elevation in steroid responders.

The Suction Ring Temporarily Raises Pressure During Surgery

The pressure rise is brief, but patients with advanced optic nerve damage may have less reserve.

The Flap Interface Can Conceal Severe Pressure Elevation

Rare interface fluid syndrome may develop when markedly raised pressure causes fluid accumulation under the LASIK flap. Central pressure measurement can then be misleadingly low.

LASIK is generally inappropriate when glaucoma is:

Uncontrolled
Moderate or advanced
Progressing
Associated with significant visual-field loss
Difficult to monitor reliably

A glaucoma suspect or patient with controlled mild disease requires individual assessment, baseline documentation and a long-term pressure-monitoring plan.

Patients With Active or Poorly Controlled Diabetes Should Not Have LASIK

Poorly controlled diabetes can cause:

Fluctuating refraction
Delayed epithelial healing
Increased infection risk
Dry-eye symptoms
Corneal neuropathy
Diabetic retinopathy
Diabetic macular oedema

Active or poorly controlled diabetes is widely regarded as a contraindication to elective corneal laser surgery.

LASIK may be considered in selected patients with:

Stable and tight glucose control
A stable refraction
No significant diabetic retinopathy
No diabetic macular oedema
No corneal neuropathy
A healthy ocular surface
No major systemic complication affecting healing

Published reviews and clinical series suggest that carefully selected patients with well-controlled diabetes may achieve acceptable results, but enhancement or healing concerns may be more relevant than in patients without diabetes.

Patients With Active Autoimmune Disease Should Not Have LASIK

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

Poor wound healing
Severe dry eye
Corneal melting
Persistent inflammation
Infection
Unpredictable refractive results

Relevant conditions may include:

Rheumatoid arthritis
Systemic lupus erythematosus
Sjögren syndrome
Scleroderma
Inflammatory bowel disease
Psoriatic disease
Other immune-mediated inflammatory disorders

Active autoimmune disease and poorly controlled systemic disease are regarded as contraindications in current reviews and regulatory guidance.

Can Stable Autoimmune Disease Ever Be Considered?

Possibly, in carefully selected cases.

Published series suggest that laser refractive surgery may be performed safely in some patients whose systemic disease is stable, well controlled and not significantly affecting the eye surface.

However, Sjögren syndrome with significant ocular-surface disease is generally a particularly poor setting for LASIK because dryness and epithelial healing are central concerns.

Assessment may require coordination with the patient’s rheumatologist or treating specialist.

Certain Medications May Be a Reason to Postpone LASIK

Medication can affect:

Tear production
Epithelial healing
Immune response
Corneal sensation
Refraction
Infection risk

Relevant medications may include:

Isotretinoin
Amiodarone
Systemic steroids
Immunosuppressants
Chemotherapy
Medication that causes severe dryness
Medication that causes fluctuating vision

Current reviews identify isotretinoin and amiodarone among drugs requiring particular caution.

Medication should never be stopped solely to qualify for elective surgery without discussion with the prescribing doctor.

Patients With Recent Ocular Herpes Should Not Have LASIK

Previous herpes simplex or herpes zoster involving the eye may be associated with:

Recurrent keratitis
Corneal scarring
Reduced corneal sensation
Irregular astigmatism
Delayed epithelial healing
Reactivation after surgery

Recent infection or significant herpes-related corneal damage is a strong reason to avoid LASIK.

A remote history may not be an absolute contraindication in every case, but it requires careful assessment of:

Time since the last episode
Number of recurrences
Corneal sensation
Corneal clarity
Use of prophylactic antiviral medication
Alternative procedures

The FDA lists ocular herpes as an important precaution requiring discussion with the surgeon.

Patients With Corneal Dystrophy, Scarring or Recurrent Erosion May Be Unsuitable

Conditions affecting the corneal epithelium or stroma may interfere with flap creation or healing.

Examples include:

Epithelial basement membrane dystrophy
Recurrent corneal erosion
Significant stromal dystrophy
Corneal scars
Reduced corneal sensation
Previous severe keratitis

Potential complications include:

Epithelial defects
Epithelial ingrowth
Irregular healing
Flap complications
Poor visual quality
Recurrent pain

Another treatment—or no elective surgery—may be safer depending on the condition.

Patients With Active Uveitis Should Not Have LASIK

Uveitis is inflammation inside the eye.

LASIK should generally be postponed while inflammation is active because surgery and postoperative medication may:

Trigger further inflammation
Complicate treatment
Increase pressure
Produce unpredictable visual recovery

A remote, isolated episode of uveitis does not automatically exclude surgery, but the cause, duration of inactivity, medication requirements and risk of recurrence must be considered.

The FDA identifies previous uveitis or iritis as a condition requiring special caution.

Patients With Retinal or Optic Nerve Disease May Not Benefit

LASIK corrects the corneal focusing error. It cannot restore vision limited by:

Amblyopia
Myopic macular degeneration
Epiretinal membrane
Macular oedema
Diabetic retinopathy
Optic nerve damage
Advanced glaucoma
Previous retinal detachment
Corneal or retinal scarring

The realistic postoperative visual potential is usually limited by the patient’s preoperative best-corrected vision.

A person whose vision does not reach normal levels with appropriate spectacles or contact lenses requires investigation before refractive surgery is considered.

LASIK Does Not Cure Amblyopia

Amblyopia is reduced visual development in an eye that did not achieve normal vision during childhood.

LASIK may reduce the refractive error but does not rebuild the visual pathways that failed to develop normally.

The eye should not be expected to see better than its established best-corrected potential.

When one eye has amblyopia, the stronger eye is functionally more important. Performing elective surgery on that eye requires particularly careful risk counselling.

Patients With Strabismus or Previous Double Vision Need Binocular Assessment

Changing the refractive balance between the eyes may:

Unmask double vision
Disturb a previously controlled eye deviation
Alter accommodation and convergence
Make monovision difficult to tolerate

Patients should disclose any history of:

Squint or strabismus
Patching during childhood
Prism glasses
Eye-muscle surgery
Intermittent double vision
Suppression or poor stereopsis

LASIK is not necessarily impossible, but additional binocular-vision testing may be required.

Patients at High Risk of Eye Trauma May Prefer SMILE or PRK

The LASIK flap becomes stable enough for normal daily activities, but the deeper interface never regains the structure of untouched cornea.

Severe direct trauma can displace or wrinkle a flap even years after surgery.

This is particularly relevant for:

Boxers
Martial artists
Wrestlers
Rugby players
Water-polo players
Military personnel
Police or tactical personnel
People in occupations with repeated facial trauma

The FDA identifies active participation in contact sports as a reason a patient may not be a good LASIK candidate.

SMILE or PRK may avoid the long-term presence of a hinged flap, although they have their own risks and still require adequate corneal structure.

Previous LASIK, PRK or Radial Keratotomy Requires Special Assessment

Additional refractive surgery may not be advisable after previous:

LASIK
PRK
SMILE
Radial keratotomy
Corneal cross-linking
Corneal transplantation
Significant corneal injury

The surgeon must assess:

Remaining corneal thickness
Existing flap or incision anatomy
Corneal shape
Stability
Previous treatment depth
Scarring
Ocular-surface health
Visual potential

The FDA advises that repeat refractive surgery should only be considered after careful assessment of the individual situation.

Patients Whose Career Restricts LASIK Should Check Before Surgery

Some employers or professional bodies may regulate:

The type of refractive procedure permitted
The minimum recovery period
Night-vision standards
Documentation requirements
Stability before returning to duty

This may be relevant to:

Pilots
Military personnel
Police officers
Commercial drivers
Divers
Emergency-service personnel

Patients should confirm occupational requirements before undergoing permanent surgery. The FDA specifically advises patients to check whether refractive surgery could jeopardise their career.

A Patient Who Is Uncomfortable With Risk Should Not Be Pressured

LASIK has a high satisfaction rate in properly selected patients, but no elective procedure is risk-free.

Potential adverse effects include:

Dry eye
Glare
Halos
Starbursts
Ghosting
Residual prescription
Flap complications
Infection
Corneal ectasia
Need for enhancement
Rare loss of best-corrected vision

The FDA advises patients to consider whether they are comfortable accepting uncertainty and whether they understand that undercorrection, overcorrection or additional treatment may occur.

A patient who is satisfied with spectacles or contact lenses may reasonably decide that even a small surgical risk is unnecessary.

What Tests Identify Patients Who Should Not Have LASIK?

A proper assessment should include more than a quick corneal-thickness measurement.

Refraction and Visual Acuity

This assesses:

Myopia or hyperopia
Astigmatism
Best-corrected vision
Prescription stability
Differences between manifest and cycloplegic refraction

Corneal Topography

Topography maps the front corneal curvature and may detect:

Asymmetric astigmatism
Keratoconus patterns
Contact lens warpage
Decentration
Irregularity

Corneal Tomography

Tomography assesses:

Anterior elevation
Posterior elevation
Thickness distribution
Pachymetric progression
The thinnest point
Corneal asymmetry

Corneal Thickness and Tissue Calculations

These estimate:

Flap thickness
Laser-ablation depth
Residual stromal bed
Percentage of tissue altered
Remaining structural reserve

Epithelial Thickness Mapping

The epithelium can partly conceal underlying stromal irregularity.

Abnormal epithelial patterns may suggest:

Early keratoconus
Contact lens warpage
Localised corneal irregularity
Previous surgery effects

Corneal Biomechanical Assessment

Biomechanical testing may add information about corneal deformation, but it cannot guarantee that ectasia will not develop.

Dry-Eye and Eyelid Examination

This may include:

Tear-film stability
Corneal and conjunctival staining
Meibomian gland assessment
Eyelid margin examination
Tear production
Corneal sensation
Symptom questionnaires

Pupil Measurement

Pupils should be assessed under dim conditions when night vision is important.

Eye Pressure and Optic Nerve Assessment

Baseline documentation is important because future pressure measurement may be affected by corneal laser surgery.

Natural-Lens Examination

This identifies early cataract or lens-related prescription change.

Dilated Retinal Examination

This is particularly important in moderate and high myopia.

Laser surgery does not remove the retinal risks associated with an elongated myopic eye.

Why Contact Lenses Must Be Stopped Before Testing

Contact lenses can temporarily change:

Corneal curvature
Astigmatism
Tear-film quality
Refraction
Corneal topography

Rigid and overnight lenses may produce more persistent warpage than standard soft lenses.

Surgery should not be planned until repeated measurements are stable after the appropriate contact lens-free interval.

What Are the Alternatives When LASIK Is Unsafe?

SMILE

SMILE may be considered when:

Myopia or myopic astigmatism is within range
Avoiding a flap is important
Early dry-eye disturbance is a concern
The cornea is otherwise structurally suitable

SMILE still permanently removes stromal tissue and is not suitable for keratoconus or inadequate corneal structure.

PRK or TransPRK

Surface ablation may be considered when:

Avoiding a flap is important
The cornea is relatively thin but structurally healthy
PRK leaves a safer tissue margin
Eye trauma is a concern

PRK involves:

More postoperative pain
Slower recovery
Corneal haze risk
Longer steroid treatment
Its own ectasia risk

Implantable Collamer Lens

ICL may be appropriate when:

Myopia is high
Corneal tissue is insufficient
The cornea is unsuitable for laser treatment
Preserving central corneal tissue is important
Internal eye anatomy is suitable

Cataract Surgery

Cataract surgery may be the correct procedure when the natural lens is already affecting:

Vision
Glare
Contrast
Prescription stability
Night driving

Spectacles or Contact Lenses

These remain safe and appropriate choices for many patients.

Not qualifying for LASIK does not mean that the eye has failed a test. It means that the expected benefit does not justify the identified risk.

Frequently Asked Questions

Who Should Definitely Not Have LASIK?

Patients with definite keratoconus, unstable refraction, insufficient corneal tissue, severe uncontrolled dry eye, active eye infection, active autoimmune disease, poorly controlled diabetes or significant cataract generally should not undergo LASIK.

Can I Have LASIK if My Prescription Is Still Changing?

Usually not yet.

Surgery should generally wait until the prescription has demonstrated stability.

Can I Have LASIK During Pregnancy?

LASIK is generally postponed until pregnancy and breastfeeding are over and the refraction has stabilised.

Can I Have LASIK With a Thin Cornea?

Possibly, but a thin cornea may not have enough structural reserve for a flap and laser ablation.

PRK or ICL may be safer in selected cases. An abnormal thin cornea may be unsuitable for all corneal laser procedures.

Can I Have LASIK With Keratoconus?

Routine LASIK should not be performed in keratoconus because it can worsen corneal instability.

Can I Have LASIK With Dry Eyes?

Mild or moderate dry eye may sometimes be treated and stabilised before surgery.

Severe or persistent dry eye may rule out LASIK.

Can I Have LASIK if I Cannot Wear Contact Lenses?

It depends on why contact lenses are intolerable.

Inconvenience or poor fit may not be a contraindication. Severe dryness, allergy or corneal inflammation may make surgery riskier.

Can I Have LASIK With Diabetes?

Possibly when diabetes is tightly controlled and there is no significant corneal, retinal or healing problem.

Poorly controlled diabetes is unsuitable.

Can I Have LASIK With an Autoimmune Disease?

Active disease is generally unsuitable.

Stable, well-controlled disease may occasionally be considered after careful ophthalmic and medical assessment.

Can I Have LASIK With Glaucoma?

Uncontrolled or advanced glaucoma is generally unsuitable.

A glaucoma suspect or patient with controlled mild disease requires individual assessment and careful baseline documentation.

Can I Have LASIK if I Have Cataract?

LASIK does not treat cataract.

When cataract is causing the symptoms, cataract surgery is usually more appropriate.

Can I Have LASIK if I Play Contact Sports?

Possibly, but the permanent flap creates a long-term trauma consideration.

SMILE or PRK may be a better structural choice.

Can I Have LASIK With Large Pupils?

Possibly.

Large pupils are not an automatic contraindication but may increase concern about glare, halos and night vision.

Can I Have LASIK if One Eye Is Lazy?

Possibly, but LASIK will not cure amblyopia.

The eye’s visual potential usually remains limited to its previous best-corrected vision.

Can I Have LASIK After Previous LASIK?

An enhancement may be possible, but only after assessing corneal thickness, flap anatomy, tomography and prescription stability.

Is High Myopia a Reason Not to Have LASIK?

Not automatically.

However, the amount of tissue required may make LASIK less safe than ICL.

Is LASIK Unsafe After Age 40?

Not solely because of age.

Presbyopia, cataract and natural-lens changes become increasingly important and may make another strategy more appropriate.

Is LASIK Safe if My Screening Says My Cornea Is Thick?

Thickness alone does not establish safety.

The corneal shape, posterior elevation, tissue distribution, treatment depth and other risk factors must also be assessed.

Is PRK Always Safe When LASIK Is Unsafe?

No.

PRK avoids a flap but still removes corneal tissue. Keratoconus and severe ocular-surface disease may rule out PRK as well.

Is SMILE Always Safe When LASIK Is Unsafe?

No.

SMILE avoids a hinged flap but still removes a stromal lenticule. It requires a structurally suitable cornea.

Is ICL Always Safer Than LASIK?

No.

ICL preserves the cornea but introduces intraocular risks. The safest procedure depends on the patient’s anatomy and risk profile.

Key Takeaway

LASIK can be highly effective, but some patients should not undergo the procedure.

LASIK should generally be avoided when there is:

Keratoconus or corneal instability
Insufficient corneal tissue
Unstable refraction
Severe or poorly controlled dry eye
Active eye infection or inflammation
Active autoimmune disease
Poorly controlled diabetes
Significant cataract
Uncontrolled or advanced glaucoma
Expectations that surgery cannot realistically fulfil

LASIK should usually be postponed during:

Pregnancy
Breastfeeding
Active myopia progression
Treatment of dry eye, blepharitis or allergy
Temporary medication-related refractive changes
Active systemic disease
Contact lens-induced corneal distortion

Additional caution is needed with:

High myopia
Large pupils
Previous ocular herpes
Controlled glaucoma
Controlled diabetes
Stable autoimmune disease
Previous eye surgery
Amblyopia or strabismus
Contact or combat sports
A family history of keratoconus

Being unsuitable for LASIK does not mean that vision cannot be corrected.

Depending on the findings, safer options may include:

SMILE
PRK or TransPRK
Implantable Collamer Lens surgery
Cataract surgery
Spectacles
Contact lenses
No surgery

The best refractive procedure is not the one with the fastest recovery or strongest marketing. It is the procedure—or non-surgical option—that provides the desired visual benefit while preserving the widest long-term safety margin for the individual eye.

References

US Food and Drug Administration. When Is LASIK Not for Me? FDA patient guidance.
US Food and Drug Administration. LASIK Quality of Life Collaboration Project.
US Food and Drug Administration. What Are the Risks and How Can I Find the Right Doctor for Me?
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