Hemi-central retinal vein occlusion. Pathogenesis, clinical features, natural history and incidence of dual trunk central retinal vein.

It has been shown that dual trunk central retinal vein (CRV) occurs in 20.3 per cent of a normal population. Confirmatory evidence has been produced by the results of anatomical, histological and micro-dissection studies. Occlusion of the single trunk of such a vein in its retrolaminar, or intraneural part, would result in a venous occlusion affecting one-half of the retina similar to that of branch retinal vein occlusion (BRVO). Yet this should be regarded as a variation of CRVO. Visual prognosis seems to be better in hemi-central retinal venous occlusion than in total CRVO. The site of development of collateral gives a clue to the site of the occlusion. Therefore, it is suggested that hemi-CRVO is a distinct entity and should not be confused with so-called hemi-spherical vein occlusion which is a variation of BRVO.