Retinal microvascular abnormalities and stroke: a systematic review

Background: Lacunar strokes account for 25% of ischaemic strokes, but their precise aetiology is unknown. Similarities between the retinal and cerebral small vessels mean that clarification of the exact relationship between retinal microvascular abnormalities and stroke, and particularly with stroke subtypes, may aid understanding of the aetiology of lacunar stroke and stroke risk. Methods: A systematic review of the literature was performed by searching Medline and Embase to October 2007 for studies in humans that investigated the association between retinal microvascular abnormalities and prevalent or incident stroke. Data and calculated summary risk ratios (sRR) were extracted for associations between retinal microvascular abnormalities and stroke, including stroke subtypes where possible, adjusted for key variables. 37 papers from 22 different studies were included with 62 975 subjects (mean age 62 years) among whom there were 2893 strokes. Stroke identification and diagnosis methods varied. Results: Retinopathy was associated with incident stroke (sRR 2.1, 95% CI 1.7 to 2.6) and prevalent stroke (sRR 2.5, 95% CI 1.4 to 4.3). Incident stroke was also associated with retinal artery embolism (sRR 2.9, 95% CI 1.6 to 5.1) and venular widening (sRR 1.4, 95% CI 1.1 to 1.7). There was significant heterogeneity between studies for some associations. There were no data on retinal microvascular abnormalities and haemorrhagic versus ischaemic stroke or ischaemic stroke subtypes. Conclusions: Retinal microvascular abnormalities are associated with stroke, but more data are required to clarify associations between specific types of retinal microvascular abnormality and stroke, as well as between different stroke subtypes. Future retinal-stroke studies should concentrate on carefully diagnosing and accurately sub-typing ischaemic stroke.