This paper discusses a technique for cornea shape measurement. Unlike the conventional method of concentric ring projection (Placido discs), this method can be used on ulcerated or scarred corneas or on non reflective surfaces. The tear film is stained with orange fluorescein and an illuminated pattern is projected through a blue filter and an image is captured through a yellow barrier filter. The points on the left and right images are matched and the cornea surface is derived. Multiple forms such as contour maps, deviations from sphericity can also be derived from this surface. Components of a digital based system are being developed and are described here.
F. A. S. Banda,
"Cornea shape measurement", Proc. SPIE 1395, Close-Range Photogrammetry Meets Machine Vision, 13952K (1 August 1990); doi: 10.1117/12.2294335; https://doi.org/10.1117/12.2294335