Am I Actually a Candidate for Laser Eye Surgery? The Measurements That Decide

The honest answer to "am I suitable for laser eye surgery" is that nobody can tell you until your eyes have been measured properly. A proportion of the people who ask us turn out not to be candidates, and a smaller number are not candidates for any refractive procedure. Below are the measurements that decide it, and what rules a person out.

What a proper suitability assessment measures

The Royal College of Ophthalmologists sets out the minimum information a surgeon should have before recommending a procedure. Its Professional Standards for Refractive Surgery (December 2024) lists visual acuity, refraction, intraocular pressures, widefield fundus images, corneal tomography including contemporary keratoconus screening indices, anterior chamber depth and mesopic pupil diameter.

None of that comes from a photograph or an online form. The same standards say the recommendation consultation should be face-to-face, not by telephone, and that surgery should not follow the same day — a cooling-off period of at least one week is recommended. Selection is what protects the patient: NICE guidance IPG164 supports photorefractive surgery "for use in appropriately selected patients".

Corneal thickness, and what is left underneath

Laser vision correction removes corneal tissue. LASIK cuts a hinged flap, then removes tissue from the bed beneath it. What remains under the flap is the residual stromal bed. If too little is left, the cornea can slowly bulge forward over months or years. That is corneal ectasia — the complication screening exists to prevent.

The old rule of thumb was to leave at least 250 microns. That is no longer treated as sufficient alone. As the American Academy of Ophthalmology's EyeNet puts it, quoting Dr Kevin Miller: "if you have a very thick cornea and you take away three-quarters of it, a 250-µm bed probably won't be good enough." The measure now used alongside it is percent tissue altered — flap thickness plus ablation depth, divided by central corneal thickness. Work led by Marcony Santhiago found figures above 40 per cent strongly associated with ectasia in corneas that looked normal beforehand.

A systematic review by Moshirfar and colleagues in Ophthalmology and Therapy (2021) estimated, in eyes with no identifiable preoperative risk factors, about 90 cases of ectasia per 100,000 eyes after LASIK, 20 per 100,000 after surface laser (PRK) and 11 per 100,000 after SMILE, across all cases reported worldwide (DOI: 10.1007/s40123-021-00383-w, via PubMed).

What rules you out: a cornea too thin for the correction you need. With a small prescription a surface procedure such as PRK or LASEK, which cuts no flap, may still be possible. With a large prescription it usually means no corneal laser at all.

Corneal shape: keratoconus and its early forms

Keratoconus is a condition in which the cornea progressively thins and steepens into a cone; laser surgery on such an eye can accelerate it badly. Early keratoconus — forme fruste keratoconus — can be invisible on a standard sight test, in an eye that sees perfectly well in glasses. It shows up only on corneal tomography, which maps both corneal surfaces and the thickness across the whole cornea.

The Moshirfar review suggests pre-existing subclinical keratoconus accounts for a larger share of "post-surgical" ectasia than has been recorded — some of what is counted as a complication may be disease that surgery unmasked. A surgeon should also ask about family history and habitual eye rubbing.

What rules you out: abnormal or asymmetric topography, thinning in the wrong place, or screening indices flagging ectasia risk. It is the commonest reason an otherwise ordinary prescription is declined.

A prescription that is still moving

Reshaping a cornea corrects the prescription you have on the day, not one that is still changing. The US Food and Drug Administration lists as a reason to reconsider: "You required a change in your contact lens or glasses prescription in the past year. This is called refractive instability." It also notes that "currently, no lasers are approved for LASIK on persons under the age of 18" (FDA).

Eighteen is a floor, not a target. Short-sightedness commonly progresses into the early twenties, which is why careful clinics defer people under about 21. Deferral is not refusal: it means returning with another year or two of stable records. What defers you: any meaningful change in the last twelve months. Bring the records; few people recall them accurately.

Pupils in the dark, and the tear film

Pupil size in dim light is why mesopic pupil diameter is on the College's list. When the pupil opens wider at night than the treated zone of the cornea, light entering through the untreated edge can produce glare, halos and starbursts, which the FDA describes as potentially debilitating for a minority. If you drive at night for a living, it matters more to you than to most.

The other is the tear film. The FDA notes that LASIK "tends to aggravate" dry eye. A meta-analysis by Shen and colleagues in PLOS ONE (2016) found that six months on, tear production was still measurably reduced after both SMILE and femtosecond LASIK, and symptom scores still worse than baseline after LASIK (DOI: 10.1371/journal.pone.0168081, via PubMed). For most people this settles; for someone who already has significant dry eye, it may not.

What rules you out: poorly controlled dry eye, an absolute contraindication in the review by Ortega-Usobiaga and colleagues in Archivos de la Sociedad Española de Oftalmología (2023). Mild dry eye is treated first and reassessed.

The rest of your health, not just your eyes

That review classes active autoimmune disease and poorly controlled diabetes as absolute contraindications, and pregnancy, breastfeeding, previous uveitis or glaucoma, and drugs including isotretinoin and amiodarone as relative ones. The FDA's list overlaps: lupus, rheumatoid arthritis, immunodeficiency states and treatment with retinoic acid or steroids "may prevent proper healing". Herpes simplex or shingles affecting the eye, glaucoma, previous eye surgery or injury, and contact sports all need discussion before anything is booked.

Pregnancy and breastfeeding shift the prescription temporarily, so a measurement taken now may not be where you settle. A reason to wait, not to give up.

Over 45? You may be asking a different question

From the mid-forties the eye's natural lens stiffens and close focus fades. That is presbyopia, and corneal laser surgery does not treat it. Someone of 52 in varifocals asking about LASIK is often really asking about lens replacement — removing the natural lens and implanting an artificial one. That is intraocular surgery, with a different and more serious risk profile.

The NHS lists among its possible complications a detached retina, permanent serious loss of vision, needing a second operation, and posterior capsule opacification. The retinal risk concentrates in longer, more short-sighted eyes: Laube and colleagues in PLOS ONE (2017), studying patients under 61 after cataract surgery or refractive lens exchange, found a cumulative retinal detachment rate of 3.55 per cent, rising to 10.2 per cent in eyes with an axial length of 25 to 28.9 mm (DOI: 10.1371/journal.pone.0184187, via PubMed). Ten per cent is not a small-print risk. It is a reason some very short-sighted people should keep their glasses.

What each procedure involves is set out on our laser eye surgery and lens replacement in Türkiye page, where we also say plainly that our eye-surgery price data is the least reliable in our set.

What we do about this

Wellness Journey is a UK-registered medical travel coordination company. We do not provide treatment: it is carried out by independent partner clinics in Cappadocia and Kayseri, licensed by the Turkish Ministry of Health and regulated in Türkiye — the CQC, GDC and GMC have no jurisdiction over care provided abroad.

Before anything is arranged, Dr Omer Selvi assesses you in person in Brighton and asks you to bring your prescription history. Some people are told there that they should not travel: sometimes "not yet", sometimes "not this procedure", sometimes "not at all". The measurements above are then repeated by the treating surgeon in Turkey, and a Brighton recommendation can still be withdrawn there.

The Royal College's standards state that "rates of conversion to surgery should not be used as a performance measure for surgeons", and that patients should not be offered time-limited discounts. A clinic that never turns anyone down is telling you what its consultation is for.

If you travel, plan for something going wrong once you are home. Read what is normal after surgery in Turkey and what is not, check your cover against our note on travel insurance for surgery abroad, and see how assessment and follow-up work. Our guide to how to check a Turkish clinic is legitimate applies to us as much as to anyone else.

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Written by Dr Omer Selvi, GMC-registered medical doctor · GMC number [INSERT]

Last reviewed: September 2026

Dr Selvi is a director of Wellness Journey, which is paid for coordinating treatment with the partner clinics described on this page. You are free to seek an independent second opinion.