Purchase this article with an account.
George A. Zikos, Arkady Selenow, Steven Ali; Comparison of Corneal Sag Based on Corneal Topographers and Optical Coherence Tomography. Invest. Ophthalmol. Vis. Sci. 2011;52(14):4178.
Download citation file:
© ARVO (1962-2015); The Authors (2016-present)
Corneal Sag values have been clinically useful for both contact lens fitting and in Orthokeratology. Calculating Corneal sag from Topography uses the radius of curvature, eccentricity value and a measurement of the HVID from the topographer image. Corneal sag can be directly measured from the anterior segment OCT image. The purpose of this study was to compare the sag values derived from measurements with two topographers and an anterior segment OCT.
We compared the steep and flat radii derived from simulated "K" measures and eccentricity values from a Optikon Keratron and a Nidek OPD-Scan Topographers for 66 eyes. We measured HVID from the respective corneal topography images and from slit lamp photography. Corneal sag values were calculated from each instrument and were compared with the sags derived from Zeiss Visante OCT Horizontal scans.
There was very good correlation between radii of curvature between the two topographers. (R^2=0.83 and 0.78 for the steep and flat radius). HVID also demonstrated good correlation (r^2=0.66) There was very poor correlation between the eccentricity values (R^2=0.01). There was poor correlation in the calculated and measured sag values between the three methods (R^2<0.2)
Corneal shape calculations that are based on corneal shape approximations such as eccentricity can vary considerably between different instrumentation.
This PDF is available to Subscribers Only