title: Morphologic and functional changes in retinal vessels associated with branch retinal vein occlusion.
abstract: OBJECTIVE
  To study the morphologic and functional changes in retinal veins of eyes affected with branch retinal vein occlusion (BRVO) by thin sectioning with optical coherence tomography (OCT).
  
  
  METHODS
  Prospective, observational, cross-sectional study.
  
  
  METHODS
  Twenty-five consecutive patients (25 eyes) with acute BRVO.
  
  
  METHODS
  Major retinal veins, arteries, and arteriovenous (A/V) crossing were examined by sequential thin sectioning by Spectralis HRA+OCT (Heidelberg Engineering, Heidelberg, Germany). The retinal blood flow was mimicked in vitro and scanned with Spectralis HRA+OCT.
  
  
  METHODS
  Morphologic characteristics of normal and BRVO-affected retinal vessels seen in OCT sections.
  
  
  RESULTS
  Cross-sectional OCT images revealed physiologic retinal vessels as oval configurations with 4 distinctive hyperreflectivities in a line. The vessel walls showed the innermost and outermost hyperreflectivity, and the blood flow showed internal paired hyperreflectivities with an hourglass shape. No eye with disturbed blood flow due to BRVO showed this internal hyperreflectivity pattern. In vitro, OCT sections of the blood within the glass tube without flow showed homogeneous reflectivities. Increased blood flow velocity resulted in the development of heterogeneous internal reflectivity and hourglass-shaped hyperreflectivities. In all eyes with acute BRVO, sequential sectioning with OCT visualized 3-dimensional vascular architecture and the intravascular conditions at the A/V crossing. At the affected A/V crossing, arterial overcrossing was seen in 17 eyes and venous overcrossing was seen in 8 eyes. In eyes with arterial overcrossing, the retinal vein seemed to run deep under the artery at the A/V crossing, and the venous lumen often appeared to be preserved even at the A/V crossing. In all eyes with venous overcrossing, the retinal vein appeared to be compressed and choked between the internal limiting membrane and the arterial wall at the A/V crossing. Optical coherence tomography sectioning showed intravenous thrombi in 21 eyes, and the thrombi were detected downstream of the A/V crossing in all the cases. The detection of thrombus was significantly associated with ischemic pattern in BRVO (P=0.036).
  
  
  CONCLUSIONS
  In eyes with BRVO, sequential thin sections with OCT visualized 3-dimensional retinal vasculature. The present OCT findings suggest that BRVO may occur by 2 different mechanisms, depending on the relative anatomic positions of the crossing vessels.
  
  
  BACKGROUND
  The author(s) have no proprietary or commercial interest in any materials discussed in this article.
authors.affiliation: Department of Ophthalmology and Visual Sciences, Kyoto University Graduate School of Medicine, Kyoto, Japan.
authors.forename: Yuki
authors.initials: Y
authors.lastname: Muraoka
authors.forename: Akitaka
authors.initials: A
authors.lastname: Tsujikawa
authors.forename: Tomoaki
authors.initials: T
authors.lastname: Murakami
authors.forename: Ken
authors.initials: K
authors.lastname: Ogino
authors.forename: Kyoko
authors.initials: K
authors.lastname: Kumagai
authors.forename: Kazuaki
authors.initials: K
authors.lastname: Miyamoto
authors.forename: Akihito
authors.initials: A
authors.lastname: Uji
authors.forename: Nagahisa
authors.initials: N
authors.lastname: Yoshimura
mesh_terms: D000208:Acute Disease; D000368:Aged; D001783:Blood Flow Velocity / Q000502:physiology; D003430:Cross-Sectional Studies; D005260:Female; D005451:Fluorescein Angiography; D006801:Humans; D008297:Male; D011446:Prospective Studies; D012161:Retinal Artery / Q000473:pathology*; D012169:Retinal Vein / Q000473:pathology*; D012170:Retinal Vein Occlusion / Q000209:etiology / Q000503:physiopathology*; D041623:Tomography, Optical Coherence; D020246:Venous Thrombosis / Q000175:diagnosis