Validation Testing of the Autocollimating Photokeratoscope*

The principle of operation of the autocollimating photokeratoscope is described briefly. It is shown how spherical test surfaces can be used to provide a valid simulation of aspheric surfaces such as the human cornea, and several trials of the instrument using these methods are described. Some of the results are useable as corrections for systematic error. An actual aspheric surface was also tested to confirm the results obtained with spherical surfaces. Corneal topography can be measured with errors at the edge of the observed field of approximately 4 μm.