A corneal model for slit-scanning elevation topography.
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 microm, 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.
Cairns
G
G
Discipline of Ophthalmology, Faculty of Medical and Health Sciences, University of Auckland, New Zealand.
Collins
A
A
McGhee
C N J
CN
D003316:Corneal Diseases / Q000175:diagnosis*; D019781:Corneal Topography / Q000295:instrumentation / Q000379:methods*; D006801:Humans; D008954:Models, Biological; D012029:Refraction, Ocular; D012680:Sensitivity and Specificity