Plasma metalloproteinase-9 in age-related macular degeneration

Sir,

Chau et al¹ described raised plasma metalloproteinase-9 (MMP-9) in age-related macular degeneration (ARMD), hypothesising that if atherosclerosis and ARMD share a common mechanism, then systemic MMP-9 and MMP-2 may be increased in patients with ARMD. While it is a plausible hypothesis, it is unclear why they have not tested it in a simple cross-sectional analysis of two groups—one with ARMD but no atherosclerosis and another group with atherosclerosis but no ARMD. Instead, each of their three sample groups includes patients with or without a history of symptomatic atherosclerosis (eg, myocardial infarction) as well as risk factors (eg, hypertension). This is pertinent as cardiovascular disease and its risk factors substantially affects MMP levels.^{2, 3}

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