Progressive loss of vision, optic disc pallor, and optociliary shunt vessels (the Hoyt-Spencer sign) constitute the clinical triad of optic nerve sheath meningiomas. However, optociliary shunt vessels may also follow central vein occlusions, and less commonly occur with a few other conditions. This report presents a comparative study of fluorescein angiograms performed on eight patients with optociliary shunt vessels. Four patients had optic nerve sheath meningiomas, and four patients had central retinal vein occlusions. The following differences in the fluorescein angiograms were noted in the two groups. In the optic nerve sheath meningioma group, the shunt vessels fill earlier (in the arteriovenous phase), the flow drains to central venous tributaries, and the late staining is hy-perfluorescent to other veins. However, in the central vein occlusion group, the shunts fill later (in the venous phase), show a flow draining to the outer disc margin, and late staining is eufluorescent with other veins. Although optic nerve sheath meningiomas and old vein occlusions are usually rather easily differentiated by a complete examination, the fluorescein angiographic patterns are not only pertinent with regards to the pathogenesis of optociliary vessels, but in certain cases may be clinically helpful in making an important clinical differentiation