title: Asymmetric distribution of arteriovenous crossings in the normal retina.
abstract: BACKGROUND
  Recently, there has been renewed interest in the orientation of the crossing retinal vessels at arteriovenous intersections, particularly as it relates to the risk of branch vein occlusion. Little is known about the distribution of the two types of crossings in the normal retina.
  
  
  METHODS
  The authors studied standard fundus photographs of 51 subjects without retinal disease. Arteriovenous crossings were analyzed for fundus location and relative orientation of the crossing vessels (vein-posterior or vein-anterior).
  
  
  RESULTS
  In the superotemporal quadrant, crossings were distributed closer to the optic disc (P < 0.001), and a greater proportion of crossings were vein-posterior (P = 0.01) than in the inferotemporal quadrant. As a result, within a 3-disc diameter (DD) radius of the optic disc, there were significantly more vein-posterior crossings in the superotemporal than in the inferotemporal quadrant (P < 0.001).
  
  
  CONCLUSIONS
  These findings further define normal retinal vascular anatomy and may explain the predilection for branch retinal vein occlusions to occur in the superotemporal quadrant.
authors.affiliation: Department of Ophthalmology, Northwestern University Medical School, Chicago, IL 60611.
authors.forename: D V
authors.initials: DV
authors.lastname: Weinberg
authors.forename: K M
authors.initials: KM
authors.lastname: Egan
authors.forename: J M
authors.initials: JM
authors.lastname: Seddon
mesh_terms: D000328:Adult; D005260:Female; D005654:Fundus Oculi; D006801:Humans; D008297:Male; D008875:Middle Aged; D009898:Optic Disk / Q000033:anatomy & histology; D010781:Photography; D012160:Retina / Q000033:anatomy & histology; D012161:Retinal Artery / Q000033:anatomy & histology*; D012169:Retinal Vein / Q000033:anatomy & histology*