Am I a candidate? The workup decides

Screening practice at partner refractive centers · Researched July 2026 · Published August 2026

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:

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.

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. 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.
• 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.
• 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.

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. 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

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