Hemi-central retinal vein occulsion. Pathogenesis, clinical features, and natural history

A two-trunked central retinal vein (CRV) in the anterior part of the optic nerve may persist as a congenital abnormality in a certain proportion of humans. One of the two trunks, like the CRV, may get occulded in the optic nerve to produce hemi-CRV occulsion (hemi-CRVO). It is shown that hemi-CRVO is a distinct entity, clincially and pathogenetically closely related to CRVO, and unrelated to branch retinal vein occlusion because of fundamental differences between the two. Hemi-CRVO clinically presents as either venous stasis retinopathy (VSR) or as hemorrhagic retinopathy (HR), usually involving one half of the retina, although ocassionally it may involve one third to two thirds of the retina. The clinical features of VSR and HR caused by hemi-CRVO are identical to those caused by CRVO. The primary object of this article is to identity hemi-CRVO, a not uncommon condition, and to describe its main clinical features.