Increased red blood cell aggregation in retinal vein occlusion.

Reversible aggregation of red blood cells (RBC) plays an important role in determining the flow properties of blood, and is the cause of the increase in blood viscosity at low shear rates. Retinal venous circulation is characterized by the combination of a low flow state and a high vascular resistance which might severely limit its capacity to adjust to high blood viscosity. These characteristics make the venous circulation in the retina particularly dependent on haemorheological factors. To test the possibility that high RBC aggregation could predispose to the onset and development of retinal vein occlusion (RVO), RBC aggregation and disaggregation (SEFAM erythroaggregameter, France) were measured in 64 patients with RVO. Results were compared to those of a group of 64 controls, similar in age, sex, smoking habit and associated pathologies. Increased RBC aggregation was observed in 52% of the patients, and the mean values showed a highly significant elevation of RBC aggregation parameters in RVO patients (+14%) when compared with controls (P less than 0.001). Subgroups were compared to study the influence of site (central versus branch), form (ischaemic versus non-ischaemic), duration and severity of the occlusion on the aggregation parameters. No significant differences were found between these various subgroups. An increase in RBC aggregability and in the shear resistance of RBC aggregates, by predisposing to circulatory stasis, is likely to contribute to the onset of RVO.