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

Background The evaluation of opitc disc topography is essential for the clinical diagnosis of primary open angle glaucoma. The purpose of this study was (1) to establish a computerized cluster formation of optic nerve head topography based on quantitative three-dimensional parameter values and (2) to describe the resulting clusters according to morphological appearence and visual fields. Patients and Methods 337 optic nerve heads (glaucomatous optic neuropathy (n = 99), glaucoma suspects (n = 159), normals (n = 79) were analyzed using laser scanning tomography. A hierarchical cluster analysis was performed based on standardized variables (optic disc area, rim area, area-ratio, cup depth, cup steepness, height variations along the contour-line). Visual fields were tested by computerized static threshold perimetry. Results A seven cluster solution met the optimizing criteria. The characteristic morphology of the clusters can be described as ''normal'' (N), ''normal, large'' (NL), ''super-normal'' (SN). ''pseudonormal'' (PN), ''glaucomalike-flat'' (GF), ''glaucomalike-steep'' (GS) and ''macropapillary'' (M). Visual fields were normal in 180 eyes. 99 eves had glaucomatous field defects, 58 eyes revealed isolated relative scotomas < 10 db. Presence and degree of visual field defects varied within the automatically classified optic disc groups considerably. Visual field defects were found in 7.7% (SN), 8.3% (N), 18.8% (NL), 33.3% (M), 37% (PN), 64.7% (GF) and 83.3% (GS) respectively. Pseudonormal discs were characterized by a flattening of the height variations along the disc border. Conclusions (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 presence of visual field defects differs considerably among the topometrically 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.