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Editors Selection IGR 9-4

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Comment by David Friedman on:

20036 Predictors of long-term progression in the Early Manifest Glaucoma Trial, Leske MC; Heijl A; Hyman L et al., Ophthalmology, 2007; 114: 1965-1972

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A statistical relationship does not automatically mean a causal relationship

These are two excellent papers. Both nicely show that glaucoma is obviously a multifactorial disease. I was specially intrigued by the observation that low blood pressure is a risk factor for progression. Low systemic blood pressure has been observed in both normal-tension and high-tension glaucoma patients that progressed despite a normalized IOP, whereas the non-progressive high tension glaucoma patients had blood pressure similar to the controls (Kaiser HJ et al., Systemic blood pressure in glaucoma patients, Graefes Arch Clin Exp Ophthalm 1993, 231: 677).

We have to keep in mind, however, that a statistical relationship does not automatically mean a causal relationship. Patients with primary vascular dysregulation, on the average, also have lower blood pressure. Therefore, hypotensive patients may progress either because they have a low perfusion pressure or because they have a dysregulation or both.

Furthermore, in studies we only find risk factors we are looking for. It is quite likely that additional (vascular) risk factors will be found in future studies.

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