Reliability of Topography Measurements in Keratoconus

Keratoconus is a progressive corneal degeneration characterized by progressive steepening and thinning of the central or paracentral cornea leading to corneal protrusion and resulting irregular astigmatism and high myopia. This disorder is usually bilateral and is linked to atopy and excessive eye rubbing, although the precise pathophysiology behind development of this condition is unclear. Keratoconus is the most common corneal degeneration in the United States, affecting between 50 and 230 subjects per 100,000 population. Early diagnosis and appropriate management of keratoconus relies greatly on accurate assessment of corneal topographic measurements. It is therefore imperative that the data obtained via corneal topography devices is accurate and reliable. The GALILEI Dual Scheimpflug Analyzer integrates Placido disc topography and dual Scheimpflug tomography to assess anterior and posterior corneal curvature data. Although there have been several studies performed assessing the ability of the Galilei to accurately distinguish keratoconus from unaffected eyes and investigating interdevice reliability between the Galilei analyzer and other tomographers, to our knowledge the repeatability of measurements obtained in this population via the Galilei device has been incompletely evaluated to date. Corneal topography data obtained via the Galilei device is relied upon heavily in clinical decision making for keratoconic patients both in the Hershey Eye Clinic and in a great number of ophthalmology practices world-wide. It is vital that the accuracy and repeatability of these measurements obtained via the Galilei device are investigated. The primary endpoint to be measured in the study will be the maximum (steepest) and minimum (flattest) keratometry values in the central zone. Secondary endpoints will be maximum keratometry across the entire area scanned, axis of corneal astigmatism, anterior and posterior best fit spheres in float mode with the diameter set to 8 mm, maximum anterior and posterior elevations, thinnest corneal thickness, and corneal asphericity at 6 mm, root mean square (RMS) of the HOAs, RMS of the third-order coma, coma axis, vertical and horizontal coma and spherical aberration.