When Is Laser Eye Surgery Not Suitable? Cornea, Prescription, Age

Transparency note: This article is published by Mapa Health, a patient coordinator based in Istanbul and authorised by the Turkish Ministry of Health (licence AK-0456). It is for information, has a commercial background and does not replace advice from an ophthalmologist.

Quick answer: Laser eye surgery is not suitable if you are younger than 18 or your prescription has changed within the last year, if the cornea is too thin or irregularly shaped, for example with keratoconus, if the prescription is very high, with very dry eyes, during pregnancy and breastfeeding, and with certain eye and general medical conditions. From your mid-40s, there is the added fact that the laser does not prevent presbyopia. Only a thorough preliminary examination shows whether you are suitable.

At a glance

Minimum age: 18 years, prescription stable for at least 12 months.

Cornea: sufficiently thick and regularly shaped, no keratoconus.

Prescription: for short-sightedness roughly up to about minus 8 to minus 10, for long-sightedness considerably less.

Factors against laser treatment: very dry eyes, pregnancy and breastfeeding, glaucoma, cataract, active inflammation, uncontrolled diabetes, certain autoimmune diseases.

Alternatives: PRK, SMILE, ICL or lens replacement, depending on the findings.

Coordinator: Mapa Health, licence AK-0456, Trustpilot 4.5 out of 5 from 108 verified reviews, more than 500 patients supported since 2020.

Why the preliminary examination matters more than any offer

Laser eye surgery permanently removes corneal tissue. This cannot be reversed. That is why it is not the offer but the preliminary examination that decides whether laser treatment goes ahead.

The examination includes measuring your prescription, mapping corneal thickness and corneal shape (topography and tomography, for example with an Oculus Pentacam), assessing the tear film, measuring intraocular pressure and examining the retina with a dilated pupil. The examination usually takes one to two hours.

Be cautious with providers who firmly promise you laser treatment before any measurement has been taken. A serious assessment is only possible after these measurements.

Age and a stable prescription

The eyes must be fully grown. That is why laser treatment is carried out from 18 at the earliest. More important than age is that your prescription has not changed for at least 12 months. In many young short-sighted people, the values continue to rise until their mid-20s. Anyone who has laser treatment too early may need glasses again later.

There is no fixed upper limit. From the mid-40s, however, almost everyone gradually loses the ability to see sharply up close. The laser corrects distance vision but does not prevent this age-related presbyopia. If you want laser treatment at this age, you should know that reading glasses may become necessary.

What suits you better over 40, laser, monovision or lens replacement, is compared in the article Over 40: Laser Eye Surgery or Lens Replacement? An Honest Comparison.

Corneal thickness and corneal shape

The cornea is the tissue the laser reshapes. It must be thick enough for sufficient stable tissue to remain after treatment. The higher the prescription, the more is removed.

There is no single figure for everyone, because it depends on the combination of starting thickness, prescription and method. If the cornea is too thin for LASIK, PRK or SMILE may sometimes be an option, because less stabilising tissue is lost. If that is not enough either, an implantable lens is often the better choice.

Shape is just as important. With keratoconus, the cornea becomes thinner and cone-shaped over time. A laser would weaken it further. Early keratoconus is often only detected by tomography. This is one of the most important reasons for a thorough measurement.

Prescription: where the laser reaches its limits

As a rough guide, short-sightedness can be treated with a laser up to about minus 8 to minus 10 dioptres, long-sightedness only to a considerably smaller extent. Astigmatism can usually be corrected at the same time. The actual limit depends on your cornea and the method.

The higher the prescription, the greater the risk that the eyes drift back somewhat towards the old values over time. Above about minus 8 dioptres this risk increases. Halos at night also tend to become more frequent.

With very high short-sightedness, an ICL is often the safer choice. A thin lens, for example the STAAR Surgical EVO ICL, is placed in front of your natural lens without removing any corneal tissue.

Dry eyes

Every laser treatment temporarily affects the corneal nerves that control the tear film. That is why dry eyes are the most common complaint in the first months.

Mildly dry eyes are often not an obstacle. They are treated before the procedure. With very severe dryness, eye doctors usually advise against laser treatment. On average, SMILE affects the corneal nerves less than LASIK and is therefore sometimes the better option for mildly dry eyes.

Eye conditions and general medical conditions

With glaucoma, cataract, active inflammation of the eye or retinal disease, laser treatment is generally not carried out. With cataract, lens replacement is the right treatment, not the laser.

Some general medical conditions also rule it out, because they affect wound healing: uncontrolled diabetes and autoimmune diseases such as lupus or rheumatoid arthritis. With well-controlled diabetes, the eye doctor decides case by case.

Some medicines affect the tear film or healing, for example isotretinoin for acne. Mention all the medicines you take at the preliminary examination.

Pregnancy, breastfeeding, occupation and sport

During pregnancy and breastfeeding, the prescription fluctuates because of hormonal changes. Eye doctors recommend waiting a few months after you stop breastfeeding.

Some professions have their own rules, for example pilots, the police or the military. Check beforehand with your employer or the relevant authority which methods are recognised.

If you practise martial arts or ball sports with a risk of impact, SMILE or PRK is often a better choice than LASIK, because no flap is created that could be displaced by a blow.

When you can return to sport, swimming and flying after the procedure is explained in the article Laser Eye Surgery Recovery: Day by Day, Flying, Work and Sport.

Before the preliminary examination: pause your contact lenses

Contact lenses change the shape of the cornea. For the measurement to be accurate, you should stop wearing them beforehand. Usually this means about one week for soft lenses and two to four weeks for rigid lenses. You receive the exact instructions with the treatment plan from Mapa Health.

The myth that "laser works for everyone"

Many advertisements give the impression that anyone who wears glasses can have laser treatment. In reality, the preliminary examination shows for some of those interested that the laser is not the best solution. A serious process accepts this: if the measurement speaks against it, no laser treatment is carried out.

Promising an exact result is just as dubious. Nobody can seriously commit to a specific dioptre outcome, because every eye heals slightly differently.

When the laser is not the right fit: the alternatives

PRK: no flap, for thinner corneas and contact sport athletes, with longer healing.

SMILE: no flap, with a small incision, mainly for short-sightedness and astigmatism, for example with the Zeiss VisuMax platform.

ICL: an additional lens inside the eye, for high prescriptions and thin corneas, without removing tissue.

Lens replacement: your natural lens is replaced, usually worthwhile from about the mid-40s to 50 when near vision is also declining, with lenses from Alcon or Zeiss, for example.

An overview of all procedures can be found in the article Which Eye Surgery Is Right for You? An Honest 2026 Guide to Laser, ICL and Lens Replacement in Turkey.

How the assessment works with Mapa Health

Mapa Health is not an eye doctor but a coordinator authorised by the Turkish Ministry of Health (licence AK-0456). Send us your current glasses prescription and, if available, earlier measurements at info@mapahealth.com. This allows an initial assessment of which methods could be considered in principle.

The final decision is made at the preliminary examination in the partner clinic in Istanbul. Only then does the eye doctor decide on the method. If the findings speak against laser treatment, the doctor explains the reasons and the alternatives. You can check the reviews on Trustpilot (4.5 out of 5 from 108 verified reviews) yourself before deciding. More about methods and the process can be found on our page about laser eye surgery in Turkey.

About the author

Tayfun Com is the founder of Mapa Health, the patient coordinator in Istanbul authorised by the Turkish Ministry of Health (licence AK-0456). Since 2020, the Mapa Health team has supported more than 500 international patients.

This article is for information only and does not replace a personal ophthalmological examination.