Eyeworld

35 EW CORNEA August 2016 Contact information Belin: mwbelin@aol.com disease. The grading system is de- pendent on tomography to produce both posterior data and thinnest point pachymetry, but this infor- mation could be available from any commercial tomographic unit (e.g., Scheimpflug, slit scanning, OCT). It is currently available on the Pen- tacam (Oculus, Wetzlar, Germany) on the "Topometric/Keratoconus Staging" display. The greatest hindrance to a clinical adoption is the lack of familiarity ophthalmologists have in using radius of curvature instead of diopters. Radius of curvature was selected to allow the same measurement of both the anterior and posterior surfaces as radius of curvature is independent on index of refraction. The posterior corneal surface is a negative lens with a low power due to the cornea/aqueous interface. Reporting the true dioptric power of the posterior cornea would be less intuitive. A sample application of the new ABCD grading system is shown in Figure 1. This is the left cornea of a 25-year-old asymptomatic male with 4.5 D of astigmatism and best spectacle distance vision (BSCVA) of 20/25. The upper left map is the anterior sagittal curvature with a mean K of 45. The Amsler-Krume- ich classification would be stage I, which fails to convey a true anatom- ic picture. The BAD display (upper right) demonstrates the prominent posterior ectasia with a final "D" of 6.49 (highly abnormal). The ABCD classification (bottom) is "A0 B2 C1 D1," which conveys the relatively normal anterior surface with a more prominent posterior ectasia. The 1-line loss of BSCVA is reflected by D1. The new ABCD classification system conveys anatomical and functional data that is missing from the Amsler-Krumeich classification. It conveys information on both an- terior and posterior corneal surfaces, is centered on the thinnest point, which is typically the region of the cone, and adds a visual acuity mea- surement as well as an indication of corneal scarring. The ABCD classifi- cation allows for a much improved description of the keratoconic cornea than was previously possible. It also may allow for more tailored treatment plans as different surfaces of the cornea may be more amena- ble to different medical or surgical intervention. The ABCD classifica- tion system is currently available on the Pentacam. EW Editors' note: Dr. Belin is professor of ophthalmology and vision science, University of Arizona, Tucson, Arizona. He has financial interests with Oculus.

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