What is corneal pachymetry, and how does it work?
Corneal pachymetry is a quick, painless eye test that measures the thickness of the cornea, the clear dome at the front of the eye. Thickness is given in micrometres (microns, µm). In a healthy adult the central cornea is about 520 to 560 µm thick, roughly half a millimetre. The test is done in two main ways. In ultrasound pachymetry a small probe touches the numbed surface of the eye for a moment and times how long a sound pulse takes to cross the cornea. In optical pachymetry, built into devices such as optical coherence tomography (OCT), Scheimpflug cameras and specular microscopes, light is used and nothing touches the eye.
The result is a single central number or a thickness map across the whole cornea. This guide explains what the number is used for, how reliable it is, what the test costs in Turkey compared with the UK, US and Germany, and how to choose a clinic. For the wider range of eye care see our eye treatments in Turkey.
Why does corneal thickness matter?
Thickness is a safety measure. Laser vision correction works by removing a thin layer of corneal tissue, and a cornea that is too thin may become weak or bulge afterwards. Thickness is also one of the signs of keratoconus, a condition in which the cornea thins and steepens. In glaucoma care it matters because standard eye-pressure readings depend slightly on corneal thickness: a thick cornea can make the pressure read falsely high and a thin one falsely low. The Ocular Hypertension Treatment Study found that a thinner central cornea was an independent risk factor for developing glaucoma in people with raised pressure, so thickness helps the doctor judge risk. Finally, a sudden increase in thickness can signal corneal swelling (oedema), as in Fuchs' dystrophy or after surgery.
Is corneal pachymetry accurate?
It is accurate enough for its purposes, with known limits. Repeat measurements on the same device usually agree within a few microns, but different devices can differ by 10 to 20 µm, and ultrasound results depend on the probe sitting on exactly the right spot and at a right angle. Corneal thickness also varies slightly through the day, being greatest on waking, and with contact lens wear or dryness. That is why a surgeon will usually repeat the test, use more than one method before refractive surgery and look at a full map rather than one number. A single thickness value does not diagnose any condition by itself; it is read with the corneal shape, the eye pressure, the optic nerve and your symptoms.
Which tests go with pachymetry: topography, OCT and others?
Pachymetry rarely stands alone. It is part of the work-up that decides whether the eye is suitable for treatment. Corneal topography maps the curvature of the front surface and is the key test for keratoconus; many modern topographers also give a thickness map. The OCT eye scan gives cross-sections of the cornea and retina without contact. The table compares how the main thickness tests differ.
| Method | Best suited to | Typical limits |
|---|---|---|
| Ultrasound pachymetry | Quick central reading; glaucoma and screening visits | Contact with the eye; sensitive to probe position |
| Optical pachymetry or OCT | Thickness maps; patients who prefer no contact | Equipment is more costly; readings can differ from ultrasound |
| Scheimpflug imaging | Keratoconus screening, laser-surgery planning | Needs a clear cornea and good fixation |
| Specular microscopy | Cell count and thickness in transplants and Fuchs' | Not suited to cloudy corneas |
For a broader overview of tests used to assess the eye before treatment, see our page on eye diagnostics.
Corneal pachymetry before laser eye surgery: what thickness is needed?
Surgeons do not rely only on the central thickness. They calculate how much tissue the planned correction will remove and how much will be left. Many surgeons aim to leave a residual stromal bed of at least about 250 to 300 µm, and they keep the planned depth of ablation within safe limits; these figures vary between surgeons and techniques and are guidance, not law. People with thinner corneas may be offered a surface method rather than a flap-based method, a smaller correction, or advised against laser surgery altogether. If you are exploring options, read about laser vision correction and ask the surgeon to show you the thickness map and the calculation for your eyes.
Pachymetry in keratoconus and glaucoma checks
In keratoconus, the thinnest point rather than the central reading is the important number, because the cone often sits off-centre; a falling thickness over time suggests progression. If the cornea is thin and progressing, doctors may discuss corneal cross-linking, a treatment that strengthens the tissue. In glaucoma care, pachymetry is done once, as thickness does not usually change, and the number is used to interpret the eye-pressure readings and risk. For glaucoma conditions in detail see glaucoma.
Corneal pachymetry cost in Turkey compared with the UK, US and Germany
The ranges below are approximate for the test alone or as part of a corneal check at an eye clinic. They are not hospital quotes, and each hospital confirms its own price in writing.
| Country | Approximate cost range |
|---|---|
| Turkey | €20 – €120 |
| United Kingdom | €40 – €200 |
| United States | €60 – €350 |
| Germany | €30 – €180 |
What changes the price: the method (ultrasound is cheaper than an OCT or Scheimpflug map), whether it is a single test or part of a full pre-surgery assessment with topography, refraction and a consultant review, and whether the result is a written report. In many hospitals the test is bundled into the consultation or the assessment for surgery and is not charged separately, so ask what is included.
What happens during the test, and is there recovery time?
For ultrasound pachymetry, an anaesthetic drop is placed in the eye, you look at a fixed point and the probe touches the cornea briefly, several times. It does not hurt, though the eye may feel slightly scratchy. Do not rub your eye for about half an hour afterwards while the numbing wears off. For optical pachymetry you rest your chin on a support and look at a light while images are taken, with no contact. There is no recovery period and you can usually go back to normal activities, including driving, straight away; if dilating drops are used for other tests, vision may be blurred for a few hours. Soft contact lenses are often removed some days before, and rigid lenses longer, because lenses change corneal shape and thickness.
Do I need to travel to Turkey for corneal pachymetry?
For the test alone, rarely. It is available at most eye clinics at home, and travelling only for this does not make sense. It becomes relevant when you are planning surgery in Turkey, such as laser correction, and the hospital repeats the measurement on its own equipment as part of the pre-operative assessment, usually on the first day. In that case it adds nothing to your trip length. Some people send existing reports in advance, which helps the team to give a provisional opinion, although the hospital will normally want to repeat key measurements before operating. A reputable hospital will also tell you honestly if the numbers show that surgery is not suitable.
How to read the result, and what are the limits?
The result is a number or a map, not a diagnosis. A central thickness around 540 µm is typical, and values between about 500 and 600 µm are within the normal range for many people; a cornea thinner than that is not automatically unhealthy, as some people simply have thin corneas. What matters is the full picture: the shape from topography, the eye pressure, your prescription and how stable it is. There are no real "before and after" images, but follow-up measurements can show change over time, which is useful for keratoconus. Risks of the test itself are minimal: a brief scratch on the surface of the eye from the probe is rare and usually heals within a day, and hygiene of the probe tip is the main safety point.
How to choose a clinic, and questions to ask
Choose an eye hospital with an ophthalmologist who reviews the result, modern topography and OCT devices, and a clear written report. Red flags are a "guaranteed suitable for laser" message before any measurement, a measurement done by one device with no repeat or second method, and a quote that bundles tests with surgery without a breakdown. Read how our process works and use the free quote page to send your existing reports. Eye-muscle conditions such as squint, described in strabismus surgery, are assessed differently and do not depend on this test. Useful questions:
- Which method will you use, and will the measurement be repeated?
- Will I receive a thickness map and a written report?
- If I am planning laser surgery, what residual thickness do you require?
- Is the test included in the consultation price?
- Do I need to stop wearing contact lenses beforehand, and for how long?
Hospitals with Eye Surgery in Turkey
Frequently asked questions
It is a painless test that measures how thick the cornea is, in microns. It can be done with a small ultrasound probe that touches the numbed eye or with a non-contact optical device such as OCT.
Most healthy adults have a central corneal thickness of about 520 to 560 microns. Thinner or thicker corneas are not always a problem, so the number is read with the corneal shape and eye pressure.
Laser surgery removes corneal tissue, so the surgeon needs to be sure enough remains afterwards. A cornea that is too thin may be advised against laser treatment or offered a different method.
Approximate prices run from about €20 to €120 in Turkey, against about €40 to €200 in the UK. It is often included in a consultation or pre-surgery assessment; the hospital confirms its price in writing.
No. With the ultrasound probe an anaesthetic drop numbs the eye, so you feel only light contact. The optical method touches nothing. The eye may feel slightly scratchy for a few minutes.
No recovery time is needed and you can normally drive and resume activities straight away. Avoid rubbing the eye for about half an hour after ultrasound, until the anaesthetic has worn off.
Repeat readings on one device agree closely, but different devices can differ by 10 to 20 microns. Surgeons therefore often repeat the test and use a thickness map rather than one number.
Eye-pressure readings depend slightly on corneal thickness. Knowing the thickness helps the doctor interpret the pressure, and a thin cornea is also a recognised risk factor for glaucoma in people with raised pressure.
No. Pachymetry measures thickness, while topography maps the curvature of the surface. They are usually done together because both are needed to judge keratoconus and suitability for laser surgery.
The test itself takes minutes and needs no stay. If it is part of a pre-surgery assessment, it is usually done on the first day and does not lengthen the trip.