Ginkgo biloba is one of the most-studied herbal extracts in existence, and its ocular blood flow research is genuinely mixed — which makes it a good example of why we present both supporting and contradicting findings rather than cherry-picking.
A 1999 crossover trial in 11 healthy volunteers found that ginkgo biloba extract significantly increased end-diastolic velocity in the ophthalmic artery compared to placebo (a 23% change, p=0.023) [1]. A longer-term study in glaucoma patients found ocular blood flow improved by roughly 8–9% after 3 and 6 months of therapy [2].
A separate randomized, placebo-controlled crossover study found that a single dose of 240mg ginkgo biloba did not meaningfully influence ocular blood flow, noting that longer-term treatment in patients with ocular vascular disease specifically would need separate investigation [3]. A broader review on ginkgo and glaucoma concluded that while published data show an increase in ocular blood flow after administration, "conclusive evidence is lacking regarding the effect on clinical outcomes" [4].