- zyx ACTA OPHTHALMOLOGICA SCANDINAVICA 1996 zyxwvut Sensitivity and specificity of structural optic disc parameters in chronic glaucoma Kjell Gunnar Gundersen, Anders Heijl and Bo Bengtsson Department of Ophthalmology,Malmo University Hospital, University of Lund, Sweden 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 zyxwvu 102 glaucoma patients were exam- ined with a raster tomographic imaging system (The Glaucoma-Sco- peTM, Ophthalmic Imaging Systems, Sacramento, CA). Glaucoma eyes were classified into four groups according to their perimetric mean devi- ation values. Minimum rim width within the 60" and 90" sectors across the vertical meridian, vertical and horizontal cup-disc ratio, rim and cup area were calculated for each optic disc. Receiver operating characteris- tics curves were set up for comparisons of the different parameters. Rep- resenting localised changes of the optic disc, minimum rim width 60"and 90" showed the best separating characteristics with sensitivity values of 91% at a fixed specificity of 90%, followed by vertical cup-disc ratio. Glo- bal 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. Key words: glaucoma - glaucoma-scopeTM - optic nerve head topography - raster tomo- graphy. Acta Ophthalmol. Scand. 1996: 74: 120-125 ptic nerve head topography is im- 0 portant for diagnosis and follow- up of glaucoma. Compared to visual field examination, topographic ana- lyses may be more objective and less time-consuming. There are also indi- cations that recognizable topographic changes of the optic nerve head may occur earlier than visual field defects (Sommer et al. 1979; Drance 1985; Jonas & Fernandez 1994). Optic nerve head topography is most often judged by ophthalmoscopy or from optic disc photographs, meth- ods that are subjective and not highly reproducible even among expert ob- servers (Varma et al. 1992).During the last decade, however, objective com- puterized methods such as laser scan- ning tomography (Burk et al. 1993;Mi- kelberg et al. 1993), optic coherence tomography (Huang et al. 1991) and raster tomography (Hoskins et al. 1993) have been introduced. Several investigators have used these instru- ments to study optic disc topography. Global topographic parameters like cup volume and rim area are reproduc- ible, and the results correlate signifi- cantly with functional indices of glau- comatous disease (Caprioli 1992; Assad & Caprioli 1992; Miller & Caprioli 1992; Burk et al. 1993). Re- sults,however,show a large overlapbe- tween glaucomatous and normal eyes. This overlap can be explained by the large normal variation of optic disc and cup size and shape (Bengtsson 1976, 1980; Heijl & Molder 1993). All glo- bal and intermediate parameters like cup/disc ratios are highly dependent on disc and cup size, and using global or intermediate parameters, small lo- calised or early uniform changes of the optic nerve head may therefore be missed. Normal rim width and shape, however, are relatively stable and inde- pendent of disc size (Bengtsson 1976, 1980; Jonas 1989). Parameters de- signed to detect localised changes of the rim width and shape may therefore be more suited to detect early glauco- matous changes. The aim of this study was to investi- gate and compare the ability of differ- ent categories of topographic parame- ters to discriminate between glauco- 120