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Qingyuan Liang, Huiyuan Liang, David T. Wong; The Arteriovenous Crossing Blocking the Macular Venous Flow Is Associated with the Majority of Branch Retinal Vein Occlusion. Invest. Ophthalmol. Vis. Sci. 2012;53(14):991.
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© ARVO (1962-2015); The Authors (2016-present)
Previous studies found that Branch Retinal Vein Occlusion (BRVO) mostly occurred at an arteriovenous (AV) crossing within 3 disc diameters (DD) from optic disc center in the temporal quadrants, which represented the macular region. BRVO crossings can be divided into 2 types: macular vein blocking (M) crossings and non-macular vein blocking (N) crossings. The former blocks macular venous flow and includes the crossing on the vein trunk after the macular vein bifurcation (Fig 1. A) or on a macular vein (Fig 1. B). The latter does not interfere with macular venous flow, and includes crossing on the vein trunk before all macular vein bifurcations (Fig 1. C), on the vein branches superior to superotemporal or inferior to inferotemporal vein trunks (Fig 1. D), or on the nasal vein branches. The macular blood flow was proved to be 3-4 times larger than other retina regions and should be slowed down more easily by an M crossing. The reduced venous flow may eventually result in BRVO. Thus, it is hypothesized that BRVO occurs more commonly with M crossings. This study compared the M and N crossings in BRVO.
A retrospective case-series study was done on the fundus images of 434 BRVO eyes (OD: 222, OS: 212) of 413 patients (male: 185, female: 228, age: 32-92 years, mean age: 69±11.4 years) between 2004 and 2009. A digital grid with coordinate and concentric circles was superimposed on the images. The locations of BRVO crossings in the temporal quadrants were marked, and the distance from optic disc center to the crossing was measured (Fig 1). The number and percentage of the M and N crossings were compared.
There were in total 432 BRVO crossings (OD: 221; OS: 211) in temporal quadrants which were 0.3-4.2 (mean 1.5±0.8) DD from the optic disc center (OD and OS: 0.3-4.2 DD, mean 1.5±0.8 DD). The total M crossings (405, 93.8%) were significantly more than the N crossings (27, 6.2%). There were no significant difference between OD (M: 211, 95.5%; N: 10, 4.5%) and OS (M: 194, 91.9%; N: 17, 8.1%).
More M crossings in BRVO suggest that the high macular circulation plays a role in BRVO development. However, it is also possible that anatomically, M crossings have a higher occurrence than N crossings. Both explanations need to be further investigated.
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