PMID: 11934207Apr 6, 2002Paper

Comparison of Placido-based, rasterstereography, and slit-scan corneal topography systems

Journal of Refractive Surgery
Fabio A Guarnieri, José C Guarnieri

Abstract

Elevation-based topography systems have received growing recognition. We compared a Placido-based (EyeSys), a rasterstereography (PAR), and a slit-scan system (Orbscan) for human subjects. Measurements were obtained from 221 eyes of 119 human subjects. We made statistical comparisons central curvature, keratometric curvatures, and meridians between the three systems. We also compared the optical pachymetry of the slit-scan system with an ultrasonic device. We analyzed cases of subclinical keratoconus, central island, photorefractive keratectomy for myopia, and hyperopia correction with arcuate keratotomy. The statistical comparison showed better correlation between the Placido-based and the rasterstereography systems in measurement of central curvature (R=0.95). The slit-scan system showed better correlation with the Placido system in the preoperative and postoperative radial keratotomy group (R=0.73) than in the group that included postoperative PRK eyes (R=0.69). Similar results were obtained for keratometric curvatures and meridians. The Orbscan pachymetry correlation with ultrasonic was R=0.69 and increased when the postoperative PRK eyes were excluded (R=0.95). Slit-projection topography and pachymetry seemed to be affecte...Continue Reading

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