What is corneal topography, and how does it work?
Corneal topography is a quick, non-contact eye test that makes a detailed map of the curvature of the cornea, the clear dome at the front of the eye. Because the cornea does most of the eye's focusing, even small irregularities in its shape blur or distort vision. The earliest systems, called Placido-disc topographers, project rings of light onto the cornea and analyse how the reflected rings are bent. Newer devices, often called corneal tomographers, use a rotating Scheimpflug camera or optical coherence tomography (OCT) to image through the cornea and map both the front and back surfaces as well as thickness. The result is a colour-coded map: cooler colours (blue, green) show flatter areas and warmer colours (orange, red) show steeper areas.
This guide explains how to read the map, what the test is used for, how it compares with related tests, what it 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.
What does a corneal topography map show?
A standard report contains several maps and a table of numbers. The curvature map (axial or sagittal) shows steepness in dioptres; the elevation map compares the cornea with an ideal reference shape and shows bumps and dips on the front and back surfaces; the thickness map shows where the cornea is thinnest. Typical findings are expressed as keratometry (the steepest and flattest curvature), astigmatism and its axis, and indices that flag suspicious shapes, such as the steepest point (often called Kmax) and the thinnest point. A normal cornea has a symmetrical bow-tie or round pattern, with a steepness of about 42 to 45 dioptres. An irregular, asymmetric pattern, especially a steep area below the centre, can point to keratoconus or other corneal conditions. The printout is a tool for the doctor, not a diagnosis you can make from colours alone.
Why is corneal topography important before laser eye surgery?
It is the screening test that decides whether laser vision correction is safe. Laser surgery reshapes the cornea by removing tissue, and a cornea that already has early, subtle keratoconus may be weakened further, leading to ectasia, a progressive bulging after surgery. Topography and tomography help identify these eyes before treatment, along with thickness measurement and your age, prescription and family history. The map is also used to plan the treatment itself, including custom or topography-guided laser treatments that correct irregular astigmatism. If you are exploring options, read about laser vision correction and ask the surgeon to explain the maps for your eyes. No single test is perfect, so reputable surgeons combine several measurements and will advise against surgery when the data are borderline.
Corneal topography in keratoconus: diagnosis and monitoring
In keratoconus the cornea thins and steepens into a cone, and topography is the key test for detecting it, often before symptoms are obvious. Signs include inferior steepening, a high Kmax, a displaced thinnest point and a back-surface elevation. Repeat maps every few months show whether the cone is progressing, which guides treatment: corneal cross-linking to strengthen the tissue, corneal ring implantation to reshape it, or specialist contact lenses. A single map can be affected by dry eye, contact lens warpage or poor fixation, which is why a doctor usually repeats it and compares maps over time, rather than relying on one.
Topography, tomography, pachymetry or OCT: which test is which?
The names overlap and are often used loosely, so it helps to know what each measures. The table summarises it.
| Test | What it measures | Typical limits |
|---|---|---|
| Placido topography | Curvature of the front surface of the cornea | Does not show the back surface or true thickness |
| Scheimpflug tomography | Front and back surfaces plus thickness map | Needs good fixation; clouded corneas image poorly |
| Corneal OCT | Cross-sections and layer thickness, without contact | Equipment is costly; maps differ slightly between brands |
| Keratometry | Curvature at a few central points only | Misses irregular or off-centre shape |
Thickness is covered in our guide to corneal pachymetry, and cross-sectional imaging in the guide to the OCT eye scan. In practice, most modern machines combine these measurements in one scan.
Other uses: contact lenses, cataract surgery and after transplants
Topography is used wherever the exact shape of the cornea matters. Specialist contact lens fitters use maps to design lenses for irregular or keratoconic corneas. Before cataract surgery, accurate curvature measurements help choose the power and, where needed, a toric lens that corrects astigmatism. After a corneal transplant or laser surgery, maps show how the shape has healed and help to find the cause of blurred vision or glare. Surgeons can also use the map to guide the removal of stitches after a graft. In short, the test is a standard part of an eye hospital work-up, and it is repeated when something changes.
Corneal topography cost in Turkey compared with the UK, US and Germany
The ranges below are approximate for the scan alone or as part of a corneal assessment. They are not hospital quotes, and each hospital confirms its own price in writing.
| Country | Approximate cost range |
|---|---|
| Turkey | €20 – €100 |
| United Kingdom | €50 – €200 |
| United States | €75 – €300 |
| Germany | €40 – €160 |
What changes the price: the type of device (a simple Placido map costs less than a Scheimpflug or OCT tomography), whether the test comes with a written interpretation by an ophthalmologist, and whether it is part of a bundle of pre-surgery tests including refraction, pachymetry and a retinal exam. Often it is included in the consultation or the assessment for surgery, so ask what is covered.
How to prepare, what happens during the test, and is there recovery?
The most important preparation is stopping contact lenses, because lenses change the shape of the cornea and can produce a false map. Surgeons commonly ask for soft lenses to be out for about one to two weeks and rigid or gas-permeable lenses for longer, often three or four weeks; follow the clinic's instruction. On the day, you rest your chin and forehead on a support and look at a target light while the device captures the image in a second or two. It does not touch the eye, needs no drops and does not hurt. A few scans are taken for each eye, and the whole test takes a few minutes. There is no recovery: you can drive and return to normal activities immediately. If your visit includes dilating drops for other tests, vision will be blurred for some hours.
Do I need to travel to Turkey for a corneal topography?
For the scan alone, seldom: it is available at most eye clinics. It is relevant if you plan treatment in Turkey, such as laser correction, cross-linking or rings, in which case the hospital repeats the map on its own equipment in the first appointment, which does not lengthen your stay. You may send existing maps in advance so the team can give a first opinion, but expect them to repeat the test, because the surgeon needs consistent measurements from their own device. Ask for a copy of the printout and the digital file so that your doctor at home can compare the maps in the future.
Accuracy, limits and safety of corneal topography
The test is safe, with no radiation and no contact. Accuracy is good for the cornea's front surface, and modern devices repeat well, but results can be affected by dry eye, recent contact lens wear, eye movement, tear film problems and scarring or swelling. Different devices produce slightly different values, so surgeons prefer to compare maps from the same machine. The result is not a diagnosis alone; it must be combined with your symptoms, an examination at the slit lamp, thickness, refraction and, where needed, repeated scans over time. There are no "before and after" photographs; the useful comparison is two maps taken months apart, which show whether the cornea is stable or changing.
How to choose a clinic, and questions to ask
Choose an eye hospital with an ophthalmologist who interprets the map, a modern tomographer and a written report. Red flags are a "guaranteed suitable for laser" message before any scan, a quote for surgery without a corneal map, and a map printed without explanation. Eye-muscle conditions such as squint, described in strabismus surgery, are assessed differently and do not depend on this test. Read how our process works and use the free quote page to send your existing maps. Useful questions:
- Which device will you use, and does it map the back surface and thickness?
- How long should I stop wearing my lenses before the test?
- Will an ophthalmologist explain the map and give me a written report?
- Is the scan included in the consultation or the surgery assessment?
- If the map is borderline, which further tests will you do before advising surgery?
Hospitals with Eye Surgery in Turkey
Frequently asked questions
It is a non-contact scan that maps the shape of the cornea, showing steep and flat areas as a colour map. It is used for laser surgery screening, keratoconus, contact lens fitting and cataract planning.
Approximate prices are about €20 to €100 in Turkey, against about €50 to €200 in the UK. It is often included in a consultation or pre-surgery assessment; the hospital confirms its price in writing.
No. Nothing touches the eye and no drops are needed. You look at a light for a second or two while the device captures the image, and the whole test takes a few minutes.
No. You can drive and carry on as usual straight away. Vision is blurred only if you also had dilating drops for another test, and that wears off in a few hours.
Yes, it is the key test, often finding early keratoconus before symptoms are clear. A diagnosis also needs thickness, an eye examination and sometimes repeat maps to see whether the shape is changing.
Laser surgery removes corneal tissue, and a cornea with hidden keratoconus could bulge afterwards. The map helps the surgeon find unsuitable eyes and plan treatment, alongside thickness and other measurements.
Stop wearing contact lenses before the test, as they change the cornea's shape. Soft lenses are often left out for one to two weeks and rigid lenses for longer, so follow your clinic's instructions.
Topography maps the front surface curvature, while tomography also images the back surface and thickness using a Scheimpflug camera or OCT. Many modern devices do both in one scan.
It is accurate and repeatable on the front surface, but dry eye, lens wear and eye movement can distort a map. Doctors often repeat the scan and compare results from the same device over time.
The scan takes minutes and needs no stay. If it is part of a pre-surgery assessment it is done at the first appointment and does not lengthen the trip.