We used an Orbscan II topography system (Bausch & Lomb) to study anterior and posterior surface abnormalities, keratometry, and topographic pachymetry in a patient with circumscribed posterior keratoconus. This system clearly showed a marked localized paracentral annular elevation in the posterior corneal surface that corresponded to an abrupt decrease in thickness and a slightly localized anterior surface bulge in the anterior float.
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Charles et al. (2005) studied this question.
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