Orbscan computerized topography: Attributes, applications, and limitations

Abstract

An extensive electronic search was undertaken in January 2004 to identify all relevant peer-reviewed publications on Orbscan slit-scanning/Placido computerized topography. Ninety-one publications were identified. These address elevation topography and best-fit sphere, accuracy and repeatability of anterior and posterior corneal elevation and keratometric maps, comparison of Orbscan-acquired data and Placido-based computerized videokeratography instruments, pachymetry measurement and correlation with ultrasound, screening eye-bank corneas, detection of keratoconus, identifying corneal ectasia after refractive surgery, and miscellaneous applications. Studies were analyzed and critically compared in relation to attributes, applications, and limitations of Orbscan corneal topography. The review highlights advantages of this technique in assessing the cornea in health and disease and after surgery and identifies specific aspects that require further investigation and clarification.

Effect of central corneal thickness on Goldmann applanation tonometry measures—a different result with different pachymeters

“…It is relevant to note that the target correlation was actually set at r=0.3 (p<0.05) in recent studies on the effect of age on the IOP-CCT relationship [15]. The present results confirm that the pachymetry output from an Orbscan II instrument can yield consistently higher thickness values than an ultrasound pachymeter [10,11]. However, the difference in thickness data generated by the pachymeters does appear to be rather dependent on the absolute thickness values, i.e.…”

“…While providing the clinician with a complete profile of the corneal thickness, the Orbscan generally appears to yield higher (thicker) values for corneal thickness than most ultrasound pachymeters [10,11]. While a case can be made that at least some of this difference can be adjusted for by application of a so-called acoustic factor to the Orbscan data (to reduce all the values by 8%), the question remains whether the adjustment yields the same IOP-CCT relationship.…”

Assessment of anterior and posterior corneal indices using two Scheimpflug analyzers

“…In addition, refractive surgery physicians who have access to both systems may be faced with the need to compare serial images of the same patient using 2 different machines. Machine threshold values were first studied on the Orbscan (Bausch and Lomb) (2,(9)(10)(11) and later on the Pentacam (12,13) . With the availability of the Galilei Dual Scheimpflug Analyzer, the primary concern was whether values obtained using the dual Scheimpflug system correlated with those obtained using the single Scheimpflug system and whether images captured by both systems can be safely compared.…”

Interchangeability between Placido disc and Scheimpflug system: quantitative and qualitative analysis

“…As new technologies have been developed, new instruments have become available, claiming performance similar to that of systems based solely on PDCT (3)(4)(6)(7)(8) . For example, the Orbscan II (Bausch & Lomb, Inc., San Dimas, CA, USA) uses a slitscanning system associated with a Placido disk to obtain curvature and elevation measurements (6,(9)(10) .…”

“…For example, the Orbscan II (Bausch & Lomb, Inc., San Dimas, CA, USA) uses a slitscanning system associated with a Placido disk to obtain curvature and elevation measurements (6,(9)(10) . The Pentacam (Oculus Inc., Lynnwood, WA, USA) stands out as a possible successor of Placido disk-based systems for obtaining images of the anterior segment.…”