A corneal topographer maps the shape of the cornea. Refractive surgeons use it before and after surgery, and contact lens practices use it to fit specialty lenses. Topographers measure in different ways, and the method decides what the device can tell you. This guide explains the differences and what to check before buying.
How topographers measure
Placido-disc topographers project a pattern of rings onto the tear film and measure how the reflection is distorted. They map the front surface of the cornea in fine detail and are quick and easy to use. The Alcon WaveLight Topolyzer VARIO is an example.
Scanning-slit systems, such as the Bausch + Lomb Orbscan IIz, pass slits of light across the eye to measure the front and back surfaces of the cornea and its thickness. Some combine this with a Placido disc.
Scheimpflug systems use a rotating camera to image the whole anterior segment, including both corneal surfaces and thickness. They are a separate category from the two above.
Match the device to your work
If you mainly need front-surface curvature for contact lens fitting or routine assessment, a Placido-disc topographer is usually enough. Refractive practices often want back-surface and thickness data too, which points to a slit-scan or Scheimpflug system.
Some topographers export data to a specific laser for topography-guided treatment. If that is why you are buying, confirm the topographer model and software version are compatible with your laser and that the export licence is active.
Software and data
Check the installed software version, whether it still receives updates, and which analysis modules are licensed. Confirm the topographer can export to your electronic records or imaging system, and that the review software runs on your computers.
Patient data must not travel with the device. Get written confirmation that the existing database has been wiped before delivery.
What to check on a pre-owned unit
Topographers are compact and well suited to the refurbished market. Confirm the following:
- Calibration against the manufacturer's test object, with the result.
- A clean, undamaged Placido cone or optics.
- Smooth joystick and chin rest movement.
- The computer, software licence keys and instrument table included.
- Patient data wiped, confirmed in writing.
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