Sensitivity and specificity of structural optic disc parameters in chronic glaucoma.

Abstract

We studied different structural optic disc parameters and their ability to discriminate between normal and glaucoma eyes using computerized raster tomography. Two hundred and seventy-six eyes of 138 normal subjects and 146 eyes of 102 glaucoma patients were examined with a raster tomographic imaging system (The Glaucoma-ScopeTM, Ophthalmic Imaging Systems, Sacramento, CA). Glaucoma eyes were classified into four groups according to their perimetric mean deviation values. Minimum rim width within the 60 degrees and 90 degrees sectors across the vertical meridian, vertical and horizontal cup-disc ratio, rim and cup area were calculated for each optic disc. Receiver operating characteristics curves were set up for comparisons of the different parameters. Representing localised changes of the optic disc, minimum rim width 60 degrees and 90 degrees showed the best separating characteristics with sensitivity values of 91% at a fixed specificity of 90%, followed by vertical cup-disc ratio. Global indices like cup and rim area and horizontal cup-disc ratio showed the poorest separation. These differences were particularly obvious in the group with mild to moderate glaucomatous visual field defects. Thus, global parameters were less likely to detect early focal glaucomatous optic nerve head changes, than parameters representing localised changes.