Comparative clinical research has focused on evaluating the accuracy of different technologies used to measure the eye’s corneoscleral surface. Two key publications, a 2020 study by Bandlitz et al. and a 2021 study by Bataille et al., have specifically investigated the differences between Fourier Profilometry1 and Scheimpflug imaging2. Both studies analyzed how these different imaging systems capture ocular data, uncovering distinct differences that practitioners should keep in mind when selecting tools for contact lens fitting.
The core finding: Data is "Not interchangeable"
A central conclusion shared by both studies is that measurements from the Eye Surface Profiler (ESP) (Fourier Profilometry) and the Pentacam CSP (Scheimpflug imaging) are not interchangeable. While both systems demonstrate strong internal repeatability, they capture and calculate corneoscleral geometry through fundamentally different mathematical and optical pathways.
What does this mean in clinical practice? Treating these different measurements as interchangeable can significantly compromise the physical fit of the lens. Because the two devices measure toricity differently, using Scheimpflug data in place of profilometry data could lead a practitioner to prescribe a spherical lens when a toric design is actually required, or vice versa.
Study overview and key data comparisons
When comparing the capabilities and data outputs of the two systems, the researchers noted several key findings:
Sagittal Height overestimation:
Both studies found a clear overestimation of sagittal height measurements from the Scheimpflug system compared to the ESP. Bandlitz et al. found that for an equal measurement area, the Scheimpflug system measured significantly greater minimal sagittal heights (by 344 µm) and maximal sagittal heights (by 280 µm). Similarly, Bataille et al. reported an overestimation across all sagittal height measurements, confirming those findings.
Scleral Best-Fit Sphere & toricity:
Bataille et al. found that the Scheimpflug system provided steeper (lower) scleral best-fit sphere measurements compared to the ESP. Additionally, Bandlitz et al. reported that toricity measurements were significantly smaller when measured with the Scheimpflug system (107 µm vs. 170 µm with Fourier Profilometry), which could lead a practitioner to prescribe a spherical lens when a toric design is actually required, or vice versa.
Possible reasons for differences between both technologies
Why do these two prominent measurement tools yield such different results? Bataille et al. explained that the discrepancies primarily stem from how each device captures and processes ocular data:
Direct projection vs. digital reconstruction
The ESP is a projection system that directly registers the surface contour, requiring no optical or distortion corrections. In contrast, Scheimpflug technology relies on mathematical digital reconstruction to build the profile.
Tissue transparency and light scattering
As Huebscher et al. observed, Scheimpflug images experience notable distortion. Bataille et al. suggested that this distortion occurs all the more when capturing non-transparent tissues like the sclera. This geometric error happens because the opaque tissue absorbs and scatters the light.
Image clarity
This light absorption and scattering create a continuous blurriness in Scheimpflug images, making it difficult for the system to precisely map the eye’s contour.
Because of the distortion in non-transparent tissue, Scheimpflug systems must apply important corrections to digitally reconstruct the scleral profile. The Bataille et al. study suggests that these proprietary reconstruction algorithms – and the fact that projection systems like the ESP do not need them – are the primary reasons behind the differing measurements.
Conclusion
When mapping the corneoscleral surface for contact lens fitting, selecting the appropriate scanning technology is vital for clinical success. Both comparative studies demonstrated that Fourier Profilometry and Scheimpflug measurements are not interchangeable. As highlighted by Bataille et al., this is largely due to how differently each technology captures and mathematically processes ocular data. Ultimately, choosing an accurate specialty lens fitting tool, strengthens clinical decision-making, enabling practitioners to design the best possible lenses for their patients.
Source 2: Bandlitz S, Esper P, Stein M, et al. Corneoscleral topography measured with fourier-based profilometry and Scheimpflug imaging. Optom Vis Sci 2020; 97:766–774.
Source 3: Huebscher H, Fink W, Steinbrück D, et al. Scheimpflug records without distortion—a mythos? Ophthalmic Res 1999;31:134–139.
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- Fourier Transform Profilometry: Represented by the Eye Surface Profiler (ESP; Eaglet Eye), which projects blue-light fringe grids onto a fluorescein-covered ocular surface to calculate height data across a chord diameter of up to 200mm. [↩]
- Scheimpflug Tomography: Represented by the Corneoscleral Profile (CSP) module of the Pentacam (Oculus), which utilizes non-contact Scheimpflug slit imaging along multiple peripheral meridians to reconstruct the anterior surface up to an chord length without requiring fluorescein. [↩]
