Am I a candidate? The workup decides
Screening practice at partner refractive centers · Researched July 2026 · Published August 2026
Candidacy is a measurement, not a quiz score. Age and prescription get you to the door; what decides LASIK is your cornea — thickness, shape regularity, and the math of how much tissue the correction would use. Roughly one in five people who ask us for LASIK leaves the workup matched to a different procedure (usually TransPRK or EVO ICL), and the final call is always made by the operating surgeon from same-day diagnostics — not by this page, and not by an online quiz.
What the diagnostic workup measures
The pre-surgical workup at a Chinese partner refractive center takes about half a day, and it is the most instrument-dense half-day in the whole trip. The core measurements, and what each one is deciding:
| Measurement | Instrument | What it decides |
|---|---|---|
| Corneal thickness (pachymetry) | Scheimpflug tomographer / ultrasound | Whether laser ablation leaves a safe residual bed — the central gate for LASIK |
| Corneal shape, front and back | Tomography (Pentacam-class) | Screens for keratoconus and irregular patterns — the non-negotiable exclusion for laser surgery |
| True refraction | Cycloplegic (dilated) refraction | Your real prescription with focusing muscles relaxed — often differs from your glasses, and it is the number the laser is programmed with |
| Pupil size in the dark | Pupillometry | Predicts night-vision symptoms; informs treatment-zone planning |
| Tear film and ocular surface | Break-up time, staining, meibography | Untreated dry eye is treated first or steers you away from flap-based surgery |
| Anterior chamber depth & endothelium | Tomography + specular microscopy | ICL-specific gates: room for the lens, and a healthy endothelial cell count |
| Retina and lens | Dilated fundus exam | High myopia carries retinal risks that get examined — and treated if needed — before any refractive surgery |
Workup content as practiced at partner centers, researched July 2026; the exact instrument list varies by hospital. Diagnostics are included in the quoted package prices — see the cost guide for what else is and isn't.
This table is the itinerary — which instruments you will meet and what each stage is for. If what you want is the other direction — a report already in your hand, and what each number on it means — the workup decoder goes value by value: the unit, the instrument that produced it, and what it is weighed against.
The residual-bed math, in plain numbers
The reason thickness dominates LASIK candidacy is arithmetic, and it's worth seeing once. A cornea might measure, say, 540 microns. A LASIK flap uses roughly 100–110 of them. The laser then removes tissue in proportion to your prescription — as a rule of thumb, on the order of 12–15 microns per diopter over a standard treatment zone. The surgeon's rule is about what must be left over: common practice keeps the untouched bed under the flap at no less than around 280–300 microns, and many surgeons also cap the total altered depth at around 40% of the original thickness. Run a −8 D correction through a 500-micron cornea and the margin disappears — which is why high prescriptions on average corneas, not just thin corneas, get routed away from LASIK. SMILE removes no flap but extracts a lenticule; TransPRK spends no flap depth at all; EVO ICL touches none of this arithmetic because nothing is removed. The numbers above are orientation, not thresholds to self-apply — surgeons weigh them together with shape, age, and prescription stability.
What rules you out — and of what
"Not a candidate" almost always means not a candidate for a specific procedure. What happens next when you hear it — the reroutes, the money, and what to settle before you fly — is set out in turned down at the workup. The useful way to see the exclusions is by how far they reach:
Rules out laser reshaping entirely
- Keratoconus, or a topography pattern suspicious for it. Removing tissue from a cornea that is already weakening is the outcome laser screening exists to prevent. This is the finding the tomographer is hunting for, and it cannot be detected without one.
- Active eye disease — infection, uncontrolled glaucoma, significant cataract. (These are treated as eye conditions first; for cataract and glaucoma care in China see our sister site, China Eye Surgery.)
Rules out LASIK, leaves alternatives open
- Insufficient thickness for the residual-bed math — the classic TransPRK or ICL redirect; the thin-corneas and high-myopia guide maps where each option takes over.
- Prescription beyond laser range — beyond roughly −8 to −10 D, tissue math and optical quality both favor ICL, which runs to about −18 D.
- Significant dry eye — a flap cuts corneal nerves and worsens it for months; surface ablation or ICL are gentler on the tear film, and treatable dry eye gets treated first. What day one measures and what a poor result does to a booked trip is set out in dry eye as a screening gate.
- Occupational impact risk — contact-sport athletes and some military roles favor flap-free options for reasons the comparison guide covers.
Rules out surgery today, not forever
- A prescription still moving — most surgeons want roughly a year of stability; operating on a moving target buys a repeat correction later.
- Pregnancy or nursing — hormones shift refraction temporarily; surgeons wait until it settles.
- Under 18 — a legal and biological floor everywhere we work; in practice most patients are mid-20s or older.
- Recent contact-lens wear — lenses mold the cornea; soft lenses come out days before the workup, rigid lenses weeks before, or the measurements are measuring your contacts, not your eyes. Overnight ortho-k is measured in months, not weeks — see what the washout requires.
What the online quizzes get wrong
Every LASIK-provider website has a thirty-second "Am I a candidate?" quiz, and this page is partly a correction to them. The quizzes ask what a form can ask: age, prescription, a yes/no on health conditions. Notice what's missing — every corneal measurement in the table above. Thickness, shape regularity, tear film, and endothelial health cannot be self-reported, and they are where real candidacy decisions are made. The result cuts both ways: quizzes clear people the tomographer would exclude (early keratoconus produces excellent glasses-corrected vision and a normal-feeling eye), and people who failed a quiz — or were declined by one clinic years ago — write themselves off when TransPRK or ICL would serve them today. A "no" from a screening quiz, a "no" from one surgeon for one procedure in one year, and a "no" from a full diagnostic workup are three very different answers. Only the last one is worth acting on.
How candidacy works when you're flying in
Medical travel adds one honest complication: you'd rather not book flights to be told no. The working sequence at partner hospitals handles it in two stages. Before you travel, we ask for whatever records you have — prescription history from your optometrist, and corneal topography or pachymetry if you've ever had it done (many optometry practices can produce both on request). That's enough to screen out clear mismatches and to match you provisionally to a procedure and a quote (the itinerary guide shows where the workup sits in each procedure's stay). On day one in China, the hospital runs the full workup fresh on its own instruments, the operating surgeon reads it, and only then is the procedure — and the final written quote — confirmed. That same-day check is also why the quoted procedure can change after arrival: the one-in-five figure is people whose provisional match didn't survive contact with a tomographer. The itinerary is built so that a procedure switch costs a conversation, not a rebooking — diagnostics sit a full day ahead of the theatre slot.
Questions people actually ask
Who is a good candidate for LASIK?
Broadly: adults 18 or over with a stable prescription for at least a year, myopia up to about −8 to −10 D (with or without moderate astigmatism), corneas thick and regular enough to leave a safe residual bed after ablation, healthy ocular surface, and no active eye disease. But every one of those gates is measured, not self-assessed — the operating surgeon decides candidacy from the diagnostic workup, and about one in five people who ask us for LASIK ends up better served by SMILE, TransPRK, or ICL.
What disqualifies you from LASIK?
The common hard stops are keratoconus or a suspicious topography pattern, corneas too thin to leave a safe residual stromal bed, an unstable prescription, active eye disease or infection, uncontrolled autoimmune conditions, pregnancy or nursing, and severe untreated dry eye. Several of these rule out flap-based LASIK specifically while leaving TransPRK or EVO ICL open — being ruled out of one procedure is not being ruled out of vision correction.
Is there an age limit for LASIK?
18 is the usual floor, and most surgeons prefer the prescription to have been stable for a year or more — which often means early-to-mid 20s in practice. There is no strict upper age limit: what changes after about 40–45 is presbyopia (age-related near-focus loss), which distance LASIK does not fix, and after 55–60 the more relevant question is often lens health rather than corneal surgery. The honest conversation about what surgery can and cannot give you at your age is part of the consult.
Can I find out if I'm a candidate before traveling to China?
Provisionally, yes: recent optometry records — prescription history, corneal thickness and topography if you have them — let the partner hospital screen out obvious mismatches and match you to a likely procedure before you book anything. But the binding decision is always made on the day, from the hospital's own full diagnostic workup. That is why the itinerary puts diagnostics on day one, before surgery is confirmed and before the final quote is signed.
What if my corneas are too thin for LASIK?
Thin corneas are the single most common reason a LASIK inquiry becomes something else. TransPRK removes no flap and uses less tissue depth, so it is often available where LASIK is not; EVO ICL removes no corneal tissue at all — a lens is placed inside the eye — and covers myopia to about −18 D. Which of the two (if either) fits your eyes is exactly what the workup exists to determine.