What it measures
A standard corneal topographer maps the cornea, the clear front window of your eye. A scleral lens, though, rests on the white of the eye, beyond the cornea. A corneo-scleral profilometer extends the map outward, measuring the height and shape of both the cornea and the sclera. Fitters use that information to choose how deep the lens must be to clear your cornea, and how its landing zone should be shaped to sit evenly. Profilometers are also used in research to measure scleral toricity, meaning how much steeper the sclera is in one direction than another.[7]
A 2025 review lists profilometry-based fitting among the advances that help achieve a fit in difficult eyes, such as those with ectasia, a previous corneal transplant, or corneal scarring.[8]
How reliable the scans are
- Repeatability. In 25 eyes of people presenting for scleral lens fitting, one profilometer gave repeat measurements of eye depth that agreed within 100 microns in 95% of cases, and the authors concluded it was repeatable enough for fitting.[5]
- Eyelids get in the way. The lids cover part of the sclera. In 20 healthy adults, holding the lids open increased the amount of measured surface substantially at some distances from center, and the instrument’s estimates for hidden areas differed between natural and held-open lid positions, most of all at the top of the eye.[4] Where the lids hide the surface, the software estimates the missing shape, and those estimates depend on how much of the eye was actually measured.[4]
- Time of day. In 109 healthy eyes scanned five times between morning and evening, the shape of the sclera didn’t change significantly over the day.[6]
What the studies show about fitting
- Ocular surface disease. In a prospective study of 15 eyes of 9 patients, scans took an average of about 10 minutes per eye. Fitting needed an average of 2.9 follow-up visits and 2.1 lenses. One eye couldn’t be fitted from the scan because of insufficient data, and one didn’t tolerate lens wear. All 13 remaining eyes were fitted successfully. The authors noted that the imaging did not remove the need for skilled clinical observation.[1]
- Efficiency. In a survey of 423 practitioners who fit scleral lenses for keratoconus, image-based fitting needed about the same first-visit time and number of lenses as trial-lens fitting. Images took a median of 10 minutes to acquire and were adequate to order a first lens a median of 80% of the time.[2]
- How often it’s used. In the same survey population, practitioners who had image-based technology used it for a median of 5% of their keratoconus fits. Most fits were still done with trial lenses.[3]
What this means for you
Profilometry is a tool, not a guarantee. A fitter with a profilometer isn’t automatically better than one without; what matters is how well they use whatever methods they have. Scans are especially helpful when your sclera is unevenly shaped, when standard lenses keep landing poorly, or when a toric or quadrant-specific landing zone is being considered.
If you’re choosing a fitter, it’s reasonable to ask which fitting methods they use and how they’d approach your eye. See questions to ask a scleral lens fitter.
Common questions
Does profilometry mean I won't need trial lenses?
Sometimes the first lens ordered from a scan is the one you keep, but not always. You may still try lenses on and need adjustments. In studies, the number of lenses and visits was similar to traditional fitting.
Is the scan uncomfortable?
It doesn't touch your eye. You look at a target while the instrument takes images, and the fitter may gently hold your eyelids open so more of the white of the eye is captured. Tell them if you need a break.
Is profilometry better than an impression?
They're different tools. A scan doesn't touch the eye but can miss areas hidden by the lids. An impression captures the surface physically, including very irregular areas. Fitters choose based on your eye and what they have available.