3-DIMENSIONAL OPTIC DISC TOPOGRAPHY BY LA SER-SCANNING TOMOGRAPHY - CLINICAL CORRELATION OF A CLUSTER-ANALYSIS

Background The evaluation of opitc disc topography is essential for th e clinical diagnosis of primary open angle glaucoma. The purpose of th is study was (1) to establish a computerized cluster formation of opti c nerve head topography based on quantitative three-dimensional parame ter values and (2) to describe the resulting clusters according to mor phological appearence and visual fields.Patients and Methods 337 optic nerve heads (glaucomatous optic neuropathy (n = 99), glaucoma suspect s (n = 159), normals (n = 79) were analyzed using laser scanning tomog raphy. A hierarchical cluster analysis was performed based on standard ized variables (optic disc area, rim area, area-ratio, cup depth, cup steepness, height variations along the contour-line). Visual fields we re tested by computerized static threshold perimetry. Results A seven cluster solution met the optimizing criteria. The characteristic morph ology of the clusters can be described as ''normal'' (N), ''normal, la rge'' (NL), ''super-normal'' (SN). ''pseudonormal'' (PN), ''glaucomali ke-flat'' (GF), ''glaucomalike-steep'' (GS) and ''macropapillary'' (M) . Visual fields were normal in 180 eyes. 99 eves had glaucomatous fiel d defects, 58 eyes revealed isolated relative scotomas < 10 db. Presen ce and degree of visual field defects varied within the automatically classified optic disc groups considerably. Visual field defects were f ound in 7.7% (SN), 8.3% (N), 18.8% (NL), 33.3% (M), 37% (PN), 64.7% (G F) and 83.3% (GS) respectively. Pseudonormal discs were characterized by a flattening of the height variations along the disc border.Conclus ions (1) Optic nerve heads may be automatically classified based upon a combination of three-dimensional topographic variables. (2) Analysis of optic disc topography and computerized perimetry are supplementary tools in the evaluation of the glaucoma patient. Visual field defects may be present within any cluster. However, the likeliness of the pre sence of visual field defects differs considerably among the topometri cally defined groups of optic nerve heads. Functional damage is to be expected in association with reduced height variations along the disc border, a small rim area and a steep cupping of the optic nerve head.