Objective: To identify fundus characteristics associated with intraocular and intra-individual variations in the distribution of macular oedema in patients with diabetes.
Methods: A review was carried out of fundus photographs and fluorescein angiograms from 226 diabetes patients who received photocoagulation treatment for macular oedema. Cases with strictly unilateral clinically significant macular oedema were identified.
Results: Strictly unilateral macular oedema was identified in five patients with non-proliferative diabetic retinopathy, three of whom demonstrated angiographic leakage confined to a single venous drainage unit, and two of whom demonstrated leakage confined to two adjacent venous drainage units opposing one another on either side of the temporal circulatory watershed. Involved drainage units were delimited by arteriovenous crossings displaying signs of venous compression. Affected eyes had more frequent and more severe crossing signs involving macular drainage than fellow eyes. Although all patients had been examined regularly, no patient had had branch retinal vein occlusion and no patient developed such occlusion during 5 years of follow-up.
Conclusion: In the present study, unilateral macular oedema in patients with diabetes was associated with angiographic leakage from venous drainage units where compression signs indicated a higher than normal likelihood of upstream congestion being present. Presumably, a modest increase in venous pressure induced macular oedema because of an underlying abnormal vascular vulnerability induced by diabetes.