Light from a set of target rings is directed onto a living cornea at near-normal incidence. The reflected real image of the target is photographed simultaneously with a profile of the cornea projected onto a scale that indicates the radius of a reference sphere. The difference of position between any target point on the photograph and the corresponding point on a photograph taken with a spherical reflector in the apparatus is used to calculate the departure of the cornea from the reference sphere. Errors of positioning of the cornea with respect to the apparatus are compensated by calculating the asphericity of the cornea for a reference sphere that most closely matches the corneal surface for the central 3-mm-diam zone. In tests, the standard deviation of calculated asphericity at the edge of the 9-mm-diam region observed on known surfaces was 4.3 μm.
© 1972 Optical Society of America
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