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J.F. Logan, S.J. Rankin, C.C. Patterson, J.A. Jackson; Heterogeneity in a Belfast Glaucoma Population . Invest. Ophthalmol. Vis. Sci. 2003;44(13):4383.
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Purpose: The aim of this study was to identify clusters of subjects with similar characteristics from within a population of Belfast glaucoma patients. Methods: The statistical technique of hierarchical cluster analysis was performed on 67 glaucoma subjects, 43 with normal tension glaucoma (NTG) and 24 with primary open angle glaucoma (POAG). A number of clinical variables were entered into the model, including Heidelberg Retina Flowmeter (HRF) parameters, diastolic ocular perfusion pressures, coagulation test of thrombin time, peak intraocular pressure (IOP), age, gender, and symptoms of migraine or vasospasm. The 'average linkage between groups' method was chosen to define inter-group distances at which division occurs. A dendrogram was produced and was examined to identify obvious clusters. >Results: Three distinct clusters of subjects were identified. The clusters were formed irrespective of the level of IOP. One group consisted of 5 subjects with NTG. They were all females with vasospastic symptoms, low IOP and low retinal blood flow measurements as measured by the HRF. A larger group of 33 subjects also demonstrated low HRF parameters and had abnormalities in the coagulation cascade. It contained 19 subjects with NTG and 14 with POAG. The third group of 29 subjects (19 NTG and 10 POAG) was more heterogeneous in nature. Conclusions: Hierarchical cluster analysis is an exploratory technique that aims to subdivide a large number of individuals into clusters that share similar characteristics. Potential discriminatory variables between the Belfast glaucoma subjects include HRF retinal blood flow measurements and coagulation abnormalities. The two large clusters contained both NTG and POAG subjects. This suggests that subjects possess similar characteristics irrespective of the level of highest intraocular pressure. Our findings are similar to results to those of the Vancouver group who, using principal component analysis, identified 2 distinct subgroups, each containing subjects with NTG and POAG (Schulzer, Drance et al, 1990). The importance of vasospastic tendencies in the pathogenesis of glaucoma is highlighted by the pure defining features of the smallest cluster of subjects in this study. These clusters of glaucoma subjects may represent different pathogenic mechanisms.
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