Dehydration is a risk factor for central retinal vein occlusion in young patients

Sir, Central retinal vein occlusion (CRVO) is a common cause of visual morbidity known to have several systemic and local risk factors (Eye Disease Case-Control Study Group 1996). Recently, there has been interest in determining whether hypercoagulable states and inherited thrombophilias also play a role in CRVO (Lahey et al. 2002). In this report, we describe four young patients who developed CRVO following an episode of dehydration. No other cause could be established despite exhaustive laboratory blood analysis. A 40-year-old white male awoke with blurred vision in his right eye the morning after a particularly hot summer night following an evening of heavy alcohol intake. He had not rehydrated. Examination identified a CRVO in the right eye. His vision improved to 6/9 within 3 months. A 55-year-old black male developed decreased right vision during his observation of the Christian festival of Lent. For the preceding 7 days, he had been fasting and abstaining from all but essential fluids. Examination revealed a non-ischaemic CRVO with no macula oedema. The subject's vision improved spontaneously to 6/9 by 6 months. A 24-year-old white male Olympic rower noted blurred right vision after a strenuous training session during an Australian summer's day. He had not rehydrated. Examination revealed a CRVO with macula oedema. His vision remains at 6/60. A 47-year-old white male presented with blurred vision in both eyes after a hot bath following a long run. He had not rehydrated and had experienced mild flu-like symptoms with a fever for the preceding 2 days. Examination revealed a right CRVO and left inferior hemi-vein occlusion. There has been no significant visual recovery in either eye. Virchow's classic axiom states that thrombosis will occur in a blood vessel when there are disturbances in the blood flow, the vessel wall or coagulation. Why such abnormalities are common at the point where the central retinal vein traverses the lamina cribrosa is unclear. In elderly patients, it is likely that changes in blood flow brought about by compression of the adjacent arteriosclerotic central retinal artery result in clotting. While similar processes appear important in younger patients, there is evidence that procoagulant states such as thrombophilia also play a role. Increased blood viscosity resulting in abnormal erythrocyte aggregation has been established as a cause of venous thrombosis in other parts of the body (Gilbert 2001). The retinal venous circulation is characterized by low flow in the presence of high vascular resistance. This combination should make the central retinal vein particularly susceptible to thrombosis in hyperviscosity states and indeed conditions such as polycythaemia and multiple myeloma have been associated with CRVO (Fong & Schatz 1993). In our patients, who experienced profound visual loss, the severe dehydrational episode would be expected to raise the blood haematocrit, producing a state of acute hyperviscosity (further exacerbated by exercise in Case 3) (Gibbs et al. 2001), resulting in venous thrombosis. The confirmation that dehydration is a risk factor for CRVO in healthy individuals (Alghadyan 1993) reinforces the need for careful history taking in these patients. As a preventive measure, it has been recommended to these patients that they avoid dehydration.