The question patients considering laser ask most often is: "Can I have laser?" The question that follows right after, and which I think is more important, is: "If not, why not?" A good surgeon first tells you who is not a candidate. Because tissue removed by laser does not come back; saying "not for now" before surgery is far better than facing a situation that is hard to put right afterwards.
Let me give the answer up front: laser is not suitable for every eye. But a "no" usually depends on a single finding; that finding has a name, a measurable limit and, most often, an alternative. I call the series of measurements and examinations I do before laser the candidate assessment. This page was not written to frighten you, but so that you know which question to take to your examination.
Short answer: eight conditions, and what is done in each
The table below summarises eight conditions that delay the operation or change the method. I explain the details one by one. If you want to see the three methods side by side, compare LASIK, SMILE and PRK (in Turkish).
| Condition | Why it is an obstacle | What is looked at | The route that usually comes up |
|---|---|---|---|
| Thin cornea, or one that would be left too thin | The tissue left after surgery may be insufficient | Thinnest-point thickness, remaining tissue, percent tissue altered | Surface ablation (PRK) or an implantable lens |
| Suspicious topography | Even an eye that looks normal may have a tendency to weaken | Corneal map, repeated over time | The suspicion is clarified first; if there is a diagnosis, keratoconus treatment, not laser |
| Marked dry eye | Measurements can be misleading, and the healing period becomes harder | Ocular surface examination, tear tests (the threshold is set at the examination) | Surface treatment first, then repeat measurement |
| Unstable prescription | The operation would be aimed at a moving target | Old prescriptions, repeated measurements | Waiting; glasses or contact lenses |
| Prescription outside the range the method can correct | The range varies with the method and the cornea | Prescription, corneal structure, method | Another method or an implantable lens |
| Pregnancy and breastfeeding | Prescription and corneal measurements can change in this period | History of the period | Postponement |
| Some eye and general health conditions | No procedure while active inflammation has not healed; in systemic disease the situation is relative | General eye examination, how well the disease is controlled | Reassessment once it is under control |
| Unrealistic expectations | The expectation and the achievable result do not match | Discussing expectations at the examination | Reframing the expectation; glasses or lenses if needed |
"You are not suitable" usually does not mean "never", but "not with this method for now". If you have heard this somewhere, ask which measurement limit made the decision. The answer may be thickness, the map, the tears or a prescription that has not settled; each points to a different route. If the answer is not clear, you have a sound reason to ask for a second opinion.
Why does the surgeon look for the "non-candidate" first? (how the candidate assessment is done)
There is no single "good/bad" number; the measurements are read together
The risk factors listed in the literature for corneal ectasia after laser (the cornea gradually thinning and bulging forward) form a list: topographic and similar mapping findings, young age, thin cornea, thin residual tissue after surgery, high myopia and high percent tissue altered.[1] No single item on the list decides on its own; the items complement each other. That is why a cornea that is thick but has a suspicious map can concern me more than one that is thinner but regular.
What to expect on examination day
At the examination the pupil is dilated with drops, your true prescription is measured and the retina is examined. Corneal mapping, thickness and tear assessment are added. Bringing your old glasses prescriptions lets me see how your prescription has evolved. If you wear contact lenses, be sure to ask how long you need to leave them out before the measurements; lenses can temporarily change the shape of the cornea. If you would rather not work out the numbers yourself, do a free pre-assessment with your prescription and corneal thickness (in Turkish).
1. Thin cornea, or tissue that would be insufficient after the procedure
Not thickness alone: remaining tissue and percent tissue altered
Knowing two concepts makes things easier. The residual stromal bed (RSB) is the thickness left in the load-bearing layer of the cornea after the procedure. The percent tissue altered (PTA) is the sum of the flap thickness and the depth of tissue removed by laser, as a proportion of the preoperative central corneal thickness. In LASIK screening the traditional criterion for remaining tissue was below 250 microns.[2] Santhiago and colleagues compared 30 eyes that developed ectasia after LASIK despite a normal preoperative map with 174 control eyes: in the ectasia group, 97% of eyes had a PTA of 40 or more and 57% had remaining tissue of 300 microns or less; the odds ratio was 223 for PTA of 40 or more and 74 for remaining tissue of 300 microns or less.[3] Both of these studies were done in LASIK eyes.
Limits in the literature, and the limit I apply
The percent tissue altered limit I apply is below 40%; in the same direction as the study above. The lower limit I look for in corneal thickness at the thinnest point is 480 microns; this is my clinical rule, there is no single publication I can show for this number, and I present it as such. I apply this limit in the same way for SMILE Pro, LASIK and No-Touch. For remaining tissue, 250 microns is traditionally cited in the literature for LASIK; in studies 300 microns or less also stands out as a risk sign. I deliberately act more cautiously: my limit for the residual stromal bed after surgery is 300 microns in LASIK, and 350 microns excluding epithelium in No-Touch (PRK) treatment done from the surface (my practice). I could not find a single accepted remaining-tissue figure for PRK in the literature; 350 microns is my clinical rule. I do not repeat my SMILE-specific thresholds on this page: the corneal thickness and tissue thresholds I apply for SMILE are set out with their sources on a separate page.
Alternative: surface ablation or an implantable lens
If the cornea is borderline, PRK, which works from the front surface of the tissue, may come up. In a meta-analysis of PRK and transPRK in patients with a mean corneal thickness below 500 microns, 946 eyes from 10 studies were assessed and no study reported postoperative ectasia. The authors, however, state that the power analysis and follow-up were insufficient for a firm judgement; all the studies were case series. The authors' positive interpretation applies to myopic and astigmatic eyes with no other eye disease or topographic abnormality.[4] PRK heals more slowly than lamellar methods; I discuss this as part of the decision. There is also the implantable lens option if the prescription is high or the cornea does not allow laser; because it has its own reasons for refusal and lifelong follow-up, I have covered it in a separate article.
If you have learned your corneal thickness, also ask "how many microns will be left after surgery, and what is my percent tissue altered?" The two numbers together tell you more than thickness alone.
2. Suspicious topography: subclinical keratoconus and the risk of ectasia
Why can even a normal-looking cornea matter?
Subclinical keratoconus is a condition in which the disease is not yet obvious but early signs can be seen on the map. The absence of these signs does not reduce the risk to zero either: in the study mentioned above, all 30 eyes that developed ectasia had normal Placido-based topography before surgery.[3] As for frequency, in eyes without an identifiable risk factor the reported ectasia rates have been calculated as 20 per 100,000 eyes for PRK, 90 for LASIK and 11 for SMILE; the rate in LASIK was found to be 4.5 times that of PRK. The authors add that the number of cases reported in SMILE may become a problem over time, and that keratoconus is a spectrum.[5] At a high-volume centre in India, 10 of 6,619 SMILE eyes developed ectasia (0.15%); in 2 of these the map was normal and in 8 it was borderline.[6] The numbers are small, but not zero; this is why I look at the map so carefully.
What does the ectasia risk score take into account?
The Ectasia Risk Score validated by Randleman and colleagues gives weighted points to the topographic pattern, the estimated remaining tissue thickness, age, preoperative corneal thickness and the glasses prescription (spherical equivalent). Of 50 eyes that developed ectasia after LASIK, 46 (92%) were correctly classified as high risk, while 3 of 50 control eyes that did not develop ectasia (6%) were wrongly counted as high risk. With traditional criteria (abnormal topography or remaining tissue below 250 microns), the proportion of eyes found to be high risk was 50%.[2] The score is a powerful aid; but it comes from a retrospective case-control study and was developed for LASIK. Rather than reading out a score to the patient, I prefer to explain which component brings you close to the limit.
Why are eye rubbing and family history asked about?
Reviews on ectasia list genetic predisposition and environmental factors such as eye rubbing among the risk factors.[7][1] This is why at the examination I ask about your eye-rubbing habit and any family history of keratoconus.
Alternative: clarify the suspicion first
If there is a suspicion on the map, the first step is not surgery but clarifying the suspicion. If keratoconus is diagnosed, the aim is no longer to remove the prescription with laser; the disease needs to be halted and, if necessary, the cornea reshaped. Options for halting and reshaping in keratoconus are described on a separate site.
This is not a postponement but a measurement plan: comparing the same map over time shows whether there is a trend in the corneal structure. I use this sentence most often when the Sirius topography gives a "borderline" result and the curvatures of the front and back surfaces of the cornea do not match each other.
3. Marked dry eye or active ocular surface disease
According to one review, dry eye is the most common complication after corneal laser surgery and a frequent cause of patient dissatisfaction. The same review stresses that detailed preoperative screening and improving the ocular surface are key to reducing the frequency and severity of later dryness.[8] In an eye that is already markedly dry, the period after laser can be harder, and the measurements can also be misleading.
My approach is this: I first treat the ocular surface and repeat the measurements afterwards. If there is blepharitis (inflammation of the eyelid margin), I first wait for it to heal. The degree of dryness is assessed at the examination; the difference between "my eye is a bit dry" and marked dry eye disease changes the decision to operate. If the tear break-up time is below 5 seconds and the Schirmer test below 5 millimetres, I assess that eye separately (the threshold I apply); this does not mean automatic cancellation of the operation, but treatment first and measurement again.
If you have complaints of dryness, say so clearly at the examination and list the drops you use. A "surface first, then measurement" plan is usually not turning the operation down but moving it to the right time.
4. Unstable prescription
"My prescription is changing" means that your glasses or contact lens prescription has measured differently recently. Laser is planned on the prescription on the day of surgery; if the prescription keeps changing afterwards, the result can drift away from the target. The condition I apply is that the prescription must have been stable for at least 1 year. This condition is the same for SMILE Pro, LASIK and No-Touch; I do not apply an additional waiting period between the ages of 18 and 21. This is why your old glasses prescriptions are valuable.
In young patients the picture is more debatable. In a study of 100 eyes of 50 patients aged 18-21 whose myopia had been documented as progressing before surgery, the median axial length rose from 26.05 mm to 26.26 mm over 3 years of follow-up after SMILE; the authors report no significant progression at group level, but variable individual elongation.[9] I do not read this as "there is no need to wait": it is a single study and individual variability is large. It only shows that the decision is not easy at a young age. I do not operate before the age of 18; in this period the main focus should be on slowing the progression of myopia.
While waiting, you continue with glasses or lenses and the measurements are repeated at intervals. If you are curious how the prescription may behave after surgery, see the article on prescription change after laser and realistic expectations.
5. Prescription outside the range the method can safely correct
You may have seen conflicting upper limits in search results, such as "up to −12" or "up to −14". One reason for this conflict is that the correctable range varies with the method, the device and the cornea; there is no single universal number. For example, an American Academy of Ophthalmology report evaluating LASIK for hyperopia states that higher hyperopic corrections, slower laser repetition rates, older laser models and a small optical zone are associated with worse stability.[10] So the same prescription carries a different expectation of stability under different conditions. Your limit is set at the examination together with your corneal structure; if your prescription is outside this range, the implantable lens option if the prescription is high or the cornea does not allow laser is discussed.
6. Pregnancy and breastfeeding
Eye changes are common in pregnancy; one review states that refractive changes are common.[11] A systematic review on ectasia reported 33 women with new-onset or progressing ectasia during pregnancy or within a year after delivery; among them were women who had previously had LASIK. The authors clearly state that the evidence is limited and heterogeneous.[12] These data are enough not for panic but for caution: because prescription and corneal measurements can change in this period, I postpone the procedure. After breastfeeding ends I wait 2 months for SMILE Pro and LASIK, and 3 months for No-Touch (my practice). This is not a "never", but a waiting plan.
7. Some eye and general health conditions
Active infection and inflammation
I do not operate while there is an active infection or inflammation in the eye; healing is awaited, and then the eye is reassessed.
Glaucoma, cataract, retinal findings
Under this heading, what decides is not so much the laser itself as the assessment of your general eye health. In the dilated examination the retina and the structure of the eye are looked at one by one; if there is a finding, managing that finding is discussed first. I do not give numbers on this, because the weight of each finding varies from person to person.
Autoimmune, rheumatic and connective tissue diseases
Many pages on the internet list these diseases as absolute contraindications. The literature is more detailed. In a retrospective study from centres in Germany comparing 1,936 eyes of 976 patients with controlled systemic disease with a control group of 1,951 people, the safety and efficacy of LASIK were high in all groups; the reoperation rate was significantly higher in the rheumatoid arthritis group (p = 0.03), and the safety index was significantly lower in the hay fever group than in controls (p = 0.004). No sight-threatening complication was documented. The authors state that selected and stable patients can achieve results comparable with healthy individuals, and that more research is needed.[13] So in this study controlled systemic disease does not appear as an absolute obstacle, but as a matter for relative assessment; however, the abstract mentions only the results of the rheumatoid arthritis and hay fever groups separately, and I leave the other disease groups (e.g. connective tissue diseases) to your doctor without drawing conclusions from it. Moreover, the study covers only stable patients. I have no source I can cite for uncontrolled disease; the decision is made together with the opinion of the doctor following your disease.
Medicines
Tell us all the medicines you take at the examination; do not stop any without asking your doctor. Once the disease is under control, a reassessment is done.
8. Unsuitable expectations
What promise can laser not make?
Laser corrects your current prescription; it cannot say that your prescription will stay at zero for life. Near vision naturally becomes harder with age (presbyopia) and laser does not prevent this; you may need reading glasses in the future. Night vision changes such as halos around lights are also a topic that needs to be discussed before surgery. Dryness is listed in one review among the frequent causes of dissatisfaction.[8] My aim in saying this is not to frighten you, but for you to meet the period after surgery with the right expectations. I have explained how the prescription may behave after surgery in the article on prescription change after laser and realistic expectations.
When the doctor does not recommend surgery
If your expectations and your measurements do not match, not recommending surgery is also a form of care. I write this not for sales, but out of honesty: sometimes the right step is to make sure you can use your glasses or lenses comfortably.
6 questions to take to the examination if you are told "you are not suitable"
You can save or share this list.
- Which measurement limit decided this: topography, thickness, prescription or tears?
- Is this a "never" or a "for now"?
- Does the situation change with another method (PRK, implantable lens)?
- If I wait, what will we measure again, and when?
- Can I have a copy of my maps and measurements?
- I would like a second opinion; which measurements should I take with me?
Getting a second opinion is not distrust of your doctor, but testing how sound the decision is. Taking your measurement printouts and old prescriptions with you lets the second doctor look at the same questions with the same data.
How can you find out where you stand?
Each of the headings above combines with a different weight in your eye. You can first get an idea with the free assessment on the site, and then come for a face-to-face examination. The pre-assessment does not replace the examination; it only clarifies which question to ask.
Would you like a pre-assessment with your corneal thickness and prescription?
Free pre-assessment with your prescription and corneal thickness (in Turkish) →Download the free guide (in Turkish) that brings these topics together in plain language.
Frequently asked questions
Laser is postponed or switched to another method when the remaining corneal tissue would be insufficient, when there is a suspicion or diagnosis of keratoconus on topography, in marked dry eye or active ocular surface disease, when the prescription is still changing, in pregnancy and breastfeeding, and in some eye and general health conditions. In most of these there is a route such as PRK, an implantable lens, waiting, or treatment first. The decision is made at the examination, with measurements.
Thickness alone does not decide; topography, the tissue that will remain after surgery and the percent tissue altered are read together. In a borderline cornea, PRK done from the surface may come up; in a meta-analysis of PRK in patients with a mean thickness below 500 microns, no ectasia was reported in 946 eyes, but the authors found the follow-up insufficient. If the prescription is high, an implantable lens is also an option.[4]
If there is a suspicion, it is clarified first; the map is repeated over time and further measurements are made if needed. If keratoconus has been diagnosed, the aim is not to remove the prescription with laser but to halt the disease and, if necessary, reshape the cornea. Even with a normal-looking map the risk is not zero, which is why the measurements are looked at as a whole. Your doctor makes the final decision at the examination.
It depends on the degree of dryness. In marked dry eye I first treat the ocular surface and repeat the measurements afterwards. According to one review, dry eye is the most common complication after laser and a frequent cause of dissatisfaction; that is why I care about this order. The decision to operate is made with the measurements taken after the surface has improved.[8]
Because laser is planned on the prescription on the day of surgery, operating while the prescription is still changing can take the result away from the target. The condition I apply is that the prescription must have been stable for at least 1 year. While waiting you continue with glasses or lenses; your old prescriptions are valuable for comparison. I do not operate before the age of 18.
I do not do it; I postpone. One review states that refractive changes are common in pregnancy; prescription and corneal measurements can change in this period. After breastfeeding ends I wait 2 months for SMILE Pro and LASIK, and 3 months for No-Touch (my practice). This is not a refusal but a waiting plan; afterwards the measurements are repeated and the decision is made again.[11]
Thresholds can vary with the doctor, the method and the measurement used; this does not mean one of them is wrong. In a study with four experienced surgeons, when an epithelial map was added to Scheimpflug corneal imaging, the suitability decision changed in 77 of 412 assessments (19%), mostly towards "suitable"; agreement between experts remained low in borderline cases. That is why asking "which measurement decided?" and getting a second opinion is legitimate.[14]
References
- Jin SX, Dackowski E, Chuck RS. "Risk factors for postlaser refractive surgery corneal ectasia." Current Opinion in Ophthalmology, 2020. PMID 32398416
- Randleman JB, Trattler WB, Stulting RD. "Validation of the Ectasia Risk Score System for preoperative laser in situ keratomileusis screening." American Journal of Ophthalmology, 2008. PMID 18328998
- Santhiago MR et al. "Association between the percent tissue altered and post-laser in situ keratomileusis ectasia in eyes with normal preoperative topography." American Journal of Ophthalmology, 2014. PMID 24727263
- Semnani F et al. "Photorefractive keratectomy in patients with thin corneas: systematic review and meta-analysis of clinical outcomes and complications." Journal of Cataract & Refractive Surgery, 2026. PMID 40947529
- Moshirfar M et al. "Ectasia After Corneal Refractive Surgery: A Systematic Review." Ophthalmology and Therapy, 2021. PMID 34417707
- Brar S, Roopashree CR, Ganesh S. "Incidence of Ectasia After SMILE From a High-Volume Refractive Surgery Center in India." Journal of Refractive Surgery, 2021. PMID 34914554
- Zhao L et al. "Comprehensive management of post-LASIK ectasia: From prevention to treatment." Acta Ophthalmologica, 2023. PMID 36774646
- Nair S, Kaur M, Sharma N, Titiyal JS. "Refractive surgery and dry eye - An update." Indian Journal of Ophthalmology, 2023. PMID 37026241
- Mastropasqua L et al. "Prospective evaluation of axial length and refractive stability after small-incision lenticule extraction in young adults with progressive myopia." Scientific Reports, 2026. PMID 42443309
- Santhiago MR et al. "LASIK for Hyperopia: A Report by the American Academy of Ophthalmology." Ophthalmology, 2026. PMID 41569212
- Khong EWC, Chan HHL, Watson SL, Lim LL. "Pregnancy and the eye." Current Opinion in Ophthalmology, 2021. PMID 34605446
- Jani D, McKelvie J, Misra SL. "Progressive corneal ectatic disease in pregnancy." Clinical and Experimental Optometry, 2021. PMID 34384340
- Saad A et al. "Surgical outcomes of laser in situ keratomileusis (LASIK) in patients with stable systemic disease." International Ophthalmology, 2024. PMID 38418603
- Mohr N et al. "Interexpert agreement on epithelial thickness mapping for refractive surgery screening: variability highlights need for standardization." Journal of Cataract & Refractive Surgery, 2026. PMID 41742376
The right decision becomes clear from your eye's measurements.
Let us clarify together whether laser is an option for you and, if not, what the next route is.