EyeWorld is the official news magazine of the American Society of Cataract & Refractive Surgery.
Issue link: https://digital.eyeworld.org/i/111385
February 2011 February 2013 The corneal topographic astigmatism (CorT) is closer in magnitude and orientation to the manifest refractive cylinder (R) than simulated keratometry. Source (all): Noel Alpins, M.D. a meridian value for each half of the cornea. Then you can do a calculation so that if you add those two together vectorially, you end up with the CorT for the whole cornea. If you vectorially subtract the two, you can then determine the dioptric difference of one half of the cornea from the other half. The term for this measure of irregularity is topographic disparity (TD),��� Dr. Alpins explained. He added, ���When you look at all the topography devices currently available, each topographer currently has different ways of quantifying corneal irregularity. This topographic disparity (TD) parameter is like a common language, where all topographers can have one common measuring gauge for irregularity.��� EW REFRACTIVE SURGERY 45 For corneal astigmatism itself, the CorT value, by representing the whole cornea not just one single Placido ring, provides some certainty in corneal measurements consistently closer to refractive cylinder, Dr. Alpins said. EW Editors��� note: Dr. Alpins and Mr. Stamatelatos have financial interests in the iASSORT software program used to support the planning and analysis of astigmatic correction. Contact information Alpins: +61.3.9584, 6122, alpins@newvisionclinics.com.au Stamatelatos: +61.3.9584, 6122, george@newvisionclinics.com.au