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The first-line drugs, prostaglandin analogues, may increase ocular blood flow (OBF) unrelated to reduction of IOP. Akaishi et al. (112) indicate the increased OBF after the repeated administration of three PG analogues, tafluprost, latanoprost, and travoprost in the conscious rabbits. It is worth to be evaluated that OBF was measured in conscious rabbit eyes, in order to exclude the effect of anesthesia and IOP reduction by PG analogues themselves. Among three drugs, the increase of OBF in tafluprost was significantly higher than travoprost and tended to be higher than latanoprost. PGI2 may be one of the causes of the increase of OBF, but the mechanism of OBF increase by PG analogues has not been fully investigated. One of the concerns of this study is that the measurement of OBF was not masked for the examiner, and another is that rabbit eyes do not respond for PG analogues in IOP reduction. The signal through the FP receptor to increase the OBF in rabbit eyes may be different from other mammals. Thus, clinical studies are expected in consideration of the effect of IOP reduction on OBF. Moreover, clinical relevance of this significant, but small increase such as 10 to 15% of OBF for glaucomatous optic neuropathy should be ensured by more evidence.