Branch retinal vein occlusion and quadratic variation in arteriovenous crossings.

To explore further the origin and clinically observed regional variation of branch retinal vein occlusion, we studied fluorescein angiograms of 42 patients (42 eyes) with branch retinal vein occlusion and a control population of 126 consecutive patients. In a statistically significant percentage of crossings, the artery was anterior to the vein in those areas of the retina clinically predisposed to branch retinal vein occlusion. Thirty-nine of the 42 patients with branch retinal vein occlusion sites had artery-anterior-to-vein crossings (P = .002), whereas 183 of all 266 arteriovenous crossings in these same eyes were similarly positioned. The artery lay anterior to the vein in significantly more temporal retinal crossings (337 of 457) than nasal retinal crossings (89 of 149; P = .002). Similarly, significantly more superotemporal quadrant crossings (164 of 209) than inferotemporal quadrant crossings (173 of 248) had the artery anterior to the vein (P = .0045). These results suggested that variation in the pattern of arteriovenous crossings may have a role in the clinical distribution of branch retinal vein occlusion.