1 August 1976 A New Photokeratoscopic Technique
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Photokeratoscopy is not an invention of the twentieth century- it goes back to the nineteenth century when Alvar Gullstrand made his first attempt in 1896. He used the Placido disc, a planar object, and photographed the reflected concentric rings from the corneal surface acting as a convex mirror. iGullstrand was unable to photograph the total corneal surface from a single picture; he had to take two or three of them to cover the corneal surface. His planar object introduced several aberrations and therefore the quality of the image was not adequate. Moreover, Gullstrand hypothesized the cornea as having a spherical surface. This simplification is seen in his dioptric diagram describing the cornea.
Sami G. El Hage, "A New Photokeratoscopic Technique," Optical Engineering 15(4), 154308 (1 August 1976). https://doi.org/10.1117/12.7971981 . Submission:

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