Tangential vs sagittal videokeratographs in the ''early'' detection of keratoconus

PURPOSE: To illustrate the difference between tangential and sagittal videokeratographs in the ''early'' (subclinical) detection of keratoconus. METHODS: The clinically normal fellow eye of a patient with unilateral keratoconus was studied with a topographer, which can display both a sagittal and a tangential map on the same page using the same color scale. RESULTS: The tangential map depicted a pattern more consistent with keratoconus and provided a maximum power of 51 diopters compared with the 46 diopters of the sagittal map. CONCLUSIONS: Tangential videokeratographs, derived from instantaneous radius of curvature algorithms, may be more useful than sagittal displays for detecting subtle corneal topographic abnormalities.