People whose vision prescription has remained stable for at least one year are often good candidates for LASIK.

LASIK is a medical innovation that has helped millions of people worldwide achieve clearer vision with less dependence on glasses or contact lenses. This laser-based procedure is precise, generally safe when performed on suitable candidates, and usually offers a relatively quick recovery.

LASIK may be used to correct several refractive errors, including:

๐ Short-sightedness or myopia
๐ Long-sightedness or hyperopia
๐ Astigmatism

However, LASIK is not automatically suitable for everyone. The decision should be based on accurate information and a comprehensive examination by an ophthalmologist.

The following are six common characteristics of people who may be suitable for LASIK.

1. You Are at Least 18 Years Old

Being at least 18 years old is one of the basic eligibility requirements for LASIK because the eyes and vision should have reached a reasonably stable stage before treatment.

During adolescence and early adulthood, the eyes may continue to develop, causing the prescription to change. Most clinics therefore accept patients aged 18 or older.

People over the age of 40-50 may still undergo LASIK if their eyes are healthy and they do not have conditions that could make surgery unsuitable, such as:

๐ Cataracts
๐ Glaucoma
๐ Retinal degeneration
๐ Significant corneal disease

The initial assessment usually includes vision testing, examination of the internal structures of the eyes, and a review of prescription changes during the previous one to two years.

2. Your Prescription Has Been Stable for at Least One Year

One of the most important requirements before LASIK is prescription stability.

If your prescription continues to change or has changed by more than approximately 0.50 dioptres within one year, the doctor may recommend postponing treatment.

LASIK does not stop the natural progression of refractive changes. It reshapes the cornea according to the prescription measured at the time of surgery.

If the prescription is still changing, vision may become blurred again after treatment, and glasses or additional correction may be required in the future.

A stable prescription improves the likelihood of achieving long-lasting results.

3. Your Prescription Is Within a Treatable Range

LASIK has limits regarding the degree of refractive error that can be corrected safely and effectively.

The surgeon will evaluate measurements obtained from several instruments, including an autorefractor and corneal-topography system.

Approximate treatment ranges may include:

๐ Myopia: Up to approximately -12.00 dioptres
๐ Hyperopia: Up to approximately +3.00 dioptres
๐ Astigmatism: Up to approximately -6.00 dioptres

These figures are general estimates. Suitability also depends on corneal thickness, corneal shape, pupil size, eye health, and the type of laser platform used.

4. Your Cornea Is Sufficiently Thick

LASIK involves creating a thin corneal flap and using a laser to reshape the tissue beneath it. The cornea must therefore be thick enough to maintain structural strength after surgery.

Corneal thickness is measured in microns using a test called pachymetry.

A normal central corneal thickness is generally around 500-550 microns. For conventional LASIK, a cornea measuring approximately 480-500 microns or more may be considered, but thickness alone does not determine eligibility.

The doctor must also calculate how much tissue will remain after treatment.

If the cornea is too thin, the risk of complications such as corneal ectasia may increase. This condition causes the cornea to weaken, bulge forwards, and become irregular after surgery.

People with thin corneas may be advised to consider another treatment, such as TransPRK or PRK, which does not require the creation of a corneal flap and generally removes less deep corneal tissue.

5. You Do Not Have Eye or Medical Conditions That Make LASIK Unsuitable

LASIK may not be appropriate for people with certain eye conditions or underlying health problems that could affect healing or treatment results.

Conditions requiring careful assessment include:

๐ Chronic dry eye: Symptoms may temporarily worsen after LASIK.

๐ Keratoconus: LASIK is generally contraindicated because the cornea is already structurally weak or irregular.

๐ Autoimmune diseases: Conditions such as systemic lupus erythematosus or rheumatoid arthritis may affect wound healing.

๐ Uncontrolled diabetes: This may delay healing and increase the risk of infection or unstable vision.

๐ Pregnancy or breastfeeding: Hormonal changes may temporarily alter the prescription and affect corneal stability.

๐ Active eye infection or inflammation: Treatment should usually be delayed until the condition has resolved.

It is important to provide the surgeon with complete information about your medical history, medications, supplements, previous eye surgery, pregnancy, and existing eye conditions.

6. You Have Realistic Expectations

Although LASIK is highly advanced and precise, it does not guarantee perfect vision for life.

People who expect never to need glasses again may be disappointed if their vision changes naturally with age.

After the age of 40, many people develop presbyopia, or age-related difficulty focusing on nearby objects. LASIK used to correct distance vision does not necessarily prevent this condition, so reading glasses may still be required.

Other considerations include:

๐ Some patients may need a minor enhancement procedure in the future.

๐ Night-time glare, halos, or light sensitivity may occur, particularly during the early recovery period.

๐ Dry-eye symptoms may temporarily increase.

๐ Healing time and visual results differ between individuals.

๐ LASIK may reduce dependence on glasses but cannot prevent ageing-related eye diseases.

A detailed discussion with an ophthalmologist will help you understand the benefits, limitations, possible side effects, and realistic outcomes.

What Happens During a LASIK Screening Examination?

If you are unsure whether LASIK is suitable for you, the next step is to schedule a comprehensive assessment at a specialised eye or LASIK centre.

The examination may include:

๐ Corneal topography
๐ Corneal-thickness measurement
๐ Measurement of pupil size in low-light conditions
๐ Tear-film and ocular-surface assessment
๐ Detailed refraction testing
๐ Eye-pressure measurement
๐ Retinal and internal-eye examination

The results help the surgeon determine whether LASIK or another vision-correction procedure is most appropriate.

Corneal Topography

Corneal topography is a non-invasive imaging test that creates a detailed map of the corneal surface.

The cornea is the clear front part of the eye. Its shape and curvature play an important role in focusing light accurately.

Corneal topography allows the ophthalmologist to assess:

๐ Corneal shape
๐ Curvature
๐ Symmetry
๐ Irregular astigmatism
๐ Areas of unusual steepness or flattening
๐ Signs of keratoconus or corneal weakness

Types of Corneal Maps

๐ Axial or sagittal map: Displays corneal curvature using different colours. Red and orange usually represent steeper areas, while green and blue represent flatter areas.

๐ Elevation map: Compares the corneal surface with a reference shape to identify elevated or depressed areas.

๐ Pachymetry map: Shows the thickness of different parts of the cornea and helps identify abnormally thin areas.

Benefits of Corneal Topography

๐ Detects keratoconus and other corneal irregularities

๐ Assesses astigmatism

๐ Supports planning for LASIK, PRK, cataract surgery, and corneal transplantation

๐ Helps select and fit specialised contact lenses

The test is painless and generally takes only a short time. The patient looks into a specialised imaging device while the system captures and analyses the corneal surface.

Corneal-Thickness Measurement or Pachymetry

Pachymetry measures the thickness of the cornea, particularly its central area.

This information is important for:

๐ Assessing LASIK and PRK safety
๐ Calculating how much tissue can be removed
๐ Evaluating glaucoma risk
๐ Monitoring corneal swelling or degeneration

Methods of Pachymetry

Ultrasound pachymetry

๐ Uses a small probe that lightly touches the cornea

๐ Usually requires anaesthetic eye drops

๐ Takes only a few seconds

๐ Provides accurate measurements

Optical pachymetry

๐ Uses light-based imaging systems such as OCT

๐ Does not require direct contact with the eye

๐ Produces high-resolution images

๐ May be suitable for repeated follow-up examinations

Common instruments include ultrasound pachymeters, OCT devices, Pentacam or other Scheimpflug imaging systems, and specular microscopes.

Measurement of Pupil Size in Low Light

In darkness, the pupil enlarges to allow more light to enter the eye. Pupil size varies according to age, medication, lighting conditions, and individual anatomy.

The pupil may measure approximately 4-8 millimetres in low-light conditions.

A large pupil in low light may increase the likelihood of night-time visual symptoms if it extends beyond the effective laser-treatment zone.

Possible symptoms include:

๐ Glare
๐ Halos around lights
๐ Starbursts
๐ Reduced night-time contrast

Pupil size may be measured using an infrared pupillometer or compatible diagnostic equipment.

Tear-Film and Ocular-Surface Assessment

The tear film helps keep the eye comfortable, protects the cornea, and supports clear vision.

It consists of three main layers:

๐ Lipid layer: Produced mainly by the meibomian glands and helps prevent rapid tear evaporation.

๐ Aqueous layer: Produced by the lacrimal glands and provides moisture.

๐ Mucin layer: Helps the tears spread evenly across the surface of the eye.

The corneal epithelium is the outermost protective layer of the cornea. Damage, inflammation, or dryness in this area may affect LASIK suitability and postoperative recovery.

Common Tear and Ocular-Surface Tests

Schirmer’s test

๐ Uses a small paper strip placed beneath the lower eyelid.

๐ Measures tear production over approximately five minutes.

๐ Very low moisture levels may indicate reduced tear production.

Tear Break-Up Time

๐ Uses fluorescein dye to evaluate how long the tear film remains stable after blinking.

๐ A short break-up time may indicate poor tear quality or evaporative dry eye.

Ocular-surface staining

๐ Uses fluorescein or lissamine green dye.

๐ Highlights damaged or inflamed areas on the cornea and conjunctiva.

Meibography

๐ Produces images of the meibomian glands within the eyelids.

๐ Helps identify gland blockage or loss associated with evaporative dry eye.

Tear osmolarity

๐ Measures the concentration of the tear film.

๐ Increased osmolarity may be associated with chronic dry-eye disease.

Treating dry eye before surgery can improve comfort, measurement accuracy, healing, and postoperative visual quality.

Comprehensive Refraction Testing

Detailed refraction testing measures the type and severity of refractive error and determines the prescription required for clear vision.

Important values include:

๐ Sphere or SPH: Indicates short-sightedness or long-sightedness.

๐ Cylinder or CYL: Indicates the amount of astigmatism.

๐ Axis: Indicates the orientation of astigmatism.

๐ Pupillary distance or PD: Measures the distance between the pupils and is mainly used when preparing glasses.

Steps in a Comprehensive Refraction Test

Auto-refraction

๐ Provides an automatic preliminary measurement.

๐ Does not require the patient to compare lenses.

Retinoscopy

๐ Uses reflected light from the retina to estimate the prescription.

๐ Useful for children or people who cannot provide reliable responses.

Subjective refraction

๐ The patient compares different lenses and selects which provides the clearest vision.

๐ Usually performed using a phoropter or trial lenses.

Keratometry or topography

๐ Measures corneal curvature.

๐ Helps assess astigmatism and plan laser treatment.

Binocular-vision testing

๐ Evaluates how well both eyes work together.

๐ Assesses focusing ability and eye-muscle coordination.

These results help the surgeon determine the appropriate procedure and laser-treatment plan.

Is LASIK Right for You?

LASIK is not suitable for everyone. However, you may be a good candidate when:

๐ You are at least 18 years old.

๐ Your prescription has remained stable for at least one year.

๐ Your refractive error is within a treatable range.

๐ Your cornea has sufficient thickness and a normal shape.

๐ Your eyes and general health are suitable for surgery.

๐ You understand the benefits, limitations, and possible risks.

For people who are tired of glasses or contact lenses, LASIK may provide clearer vision and greater convenience. However, the final decision should be made after a comprehensive eye examination and consultation with a qualified ophthalmologist.

 

Reference :

Piyavate Blog Lasik Test
ArokaGO Providers Piyavate Hospital