Since the introduction of the ophthalmometer into clinical ophthalmology, many authors have studied the variations of the curvature of the cornea. Steiger, who was the first to apply statistical methods to this study, found that the variations of the corneal curvature behaved very regularly and followed the law of Gauss. The next logical step was to investigate the distribution of the various degrees of corneal astigmatism over the three main refractive states, emmetropia, myopia and hyperopia. This classification, mainly on Steiger's suggestion that all the refractive states should be considered as physiologic variations of normal refraction, was learned to be an arbitrary procedure which was not justified by any biologic facts. Therefore, the frequency of the various degrees of corneal astigmatism was determined separately for each refractive state. Extensive studies of this type, using skiascopy without cycloplegia and manifests for the determination of axial refraction and then correlating
KRONFELD PC, DEVNEY C. THE FREQUENCY OF ASTIGMATISM. Arch Ophthalmol. 1930;4(6):873–884. doi:10.1001/archopht.1930.00810140085006
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