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A. S. Khouri, B. C. Szirth, K. S. Shahid, R. D. Fechtner; Software Assisted Optic Nerve Assessment for Glaucoma Screening. Invest. Ophthalmol. Vis. Sci. 2007;48(13):2767.
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Increased optic nerve (ON) cup-to-disc ratio (CDR) may indicate glaucoma, a silent vision threatening disease (VTD). Screening for glaucoma with tonometry alone is not sensitive or specific. Assessment of ON is the single best method for glaucoma screening but requires a trained evaluator. We evaluated new software to calculate CDR from ON images.
Digital ON images from 14 subjects acquired during VTD screening in accordance with American Telemedicine Association recommendations, using a Canon CR-DGi non-mydriatic 45 degree camera with 8.2 Mpixel resolutionwere used in the analysis. Right eye images were chosen. All images were captured in DICOM format, and saved on a computer. No image enhancement or compression was performed. Images were evaluated on a 32 bit, 1600x1200 pixel resolution monitor (Advan Int’l Corp., Fremont, CA). EyeScape software (v126.96.36.1997, Synemed, Inc., Benicia, CA) was used to view and determine CDR. Software CDR determination requires an operator to place disc and cup contour lines. The software allowed initial placement of contour lines through 8 circumferential control points. Contour lines were fine tuned through 20 additional control points when needed. Once lines were placed, locked, and saved, the software provided an overall CDR (range 0.00 to 1.00), and CDR at any radial ON location. Contour lines were created by three individuals, a glaucoma specialist (GS), an optometrist, and a college student with no ophthalmic training. Images were logged and accessed by raters on separate days. The 3 raters were masked to each other’s evaluations.
A total of 42 ON evaluations were analyzed. Overall CDR mean, standard deviation (SD), standard error of the mean (SEM), and mean difference from GS CDR evaluation are shown in table. The student had a small but statistically significant greater CDR. Reproducibility was similar for all operators.
Evaluation of ON images for CDR can be performed using EyeScape software, by individuals with different levels of ophthalmic training. Accurate determination of CDR is important in screening for VTD, and can aid in identifying subjects with suspicious ON in need of specialty eye care.
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