Background: Retinal venous circulation is characterized by the combination of a low flow state and a high vascular resistance, which would make it particularly dependent on blood viscosity. Erythrocyte aggregation is the chief determinant of blood viscosity at low shear rates. Recent studies have demonstrated increased erythrocyte aggregation in many systemic vascular disorders and also in retinal vein occlusion.
Methods: To assess the possible role of abnormal hemorheologic findings in the pathogenesis of central retinal vein occlusion (CRVO), the authors retrospectively studied erythrocyte aggregation and hematocrit and fibrinogen levels in 33 patients with CRVO and without any known risk factors (diabetes, hypertension, smoking, hyperlipidemia, cardiovascular disease, glaucoma). Erythrocyte aggregation was assessed with a light back-scattering method. Results were compared with those of a group of 33 age- and sex-matched controls.
Results: Eleven (33%) of the 33 patients with CRVO had abnormal hemorheologic findings. Erythrocyte aggregation was highly significantly increased in the CRVO group when compared with the control group (P < 0.0001), as was the hematocrit level (P < 0.05). In addition, the proportion of patients with abnormal blood rheologic tests was greater (50%) in the subgroup of patients who initially had nonischemic CRVO that worsened into an ischemic CRVO during the follow-up.
Conclusion: These data suggest that abnormal hemorheologic findings could affect the pathogenesis of CRVO, and perhaps be predictive of an aggravation. The latter hypothesis needs to be confirmed in a larger, prospective study.