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A corneal model for slit‐scanning elevation topography
Author(s) -
Cairns G.,
Collins A.,
McGhee C. N. J.
Publication year - 2003
Publication title -
ophthalmic and physiological optics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.147
H-Index - 66
eISSN - 1475-1313
pISSN - 0275-5408
DOI - 10.1046/j.1475-1313.2003.00107.x
Subject(s) - elevation (ballistics) , corneal topography , refractive index , slit , optics , cornea , ray tracing (physics) , keratoconus , ophthalmology , materials science , mathematics , physics , medicine , geometry
Computerised videokeratography is increasing in sophistication and accuracy. The Orbscan II Videokeratographer combines the advantages of Placido derived and slit‐scanning derived topography, to acquire shape information on the posterior surface of the cornea. The purpose of this paper is to construct a model of slit‐scanning elevation topography and highlight potential sources of variation in this methodology. Ray tracing calculations were performed on a defined, theoretical, spherical model to obtain a pachymetric measurement. These calculations were tested by comparing the pachymetry measurement derived from the model, over a refractive index shift from 1.376 to 1.400 with the pachymetry measurement obtained by Orbscan II, of a human eye, with an identical alteration in refractive index. The two methods of measurement differed by only 0.157 μm, suggesting that the model is a good representation of slit‐scanning elevation topography, and that refractive index variations have only a minimal effect on Orbscan II pachymetry measurement.