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PubMed1987

A longitudinal study of the age dependence of human ocular refraction--III. The mediation of changes from direct to inverse astigmatism examined by means of matrices of transition probabilities.

This study enquires into the manner in which the axis of astigmatism changes in the course of individual refractive histories. Specifically, two related problems are addressed: (1) how is the change from direct to inverse astigmatism mediated, and (2) what is the range of relative proportions of each of four variables (spherical ametropia, direct, inverse and oblique astigmatism) that occur in a sample population so that it can be considered randomly sampled and well distributed? Solutions to both problems are obtained by calculation of the probabilities with which transitions between such variables occur. A moderately sized longitudinal sample is used to demonstrate the new method. One of the conclusions is that the biological strategy for the mutation of the astigmatic axis is multi-faceted and that there is unlikely to be a single cause which can explain the process by which inverse astigmatism is achieved.

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