Recent studies reported that parapapillary microvascular dropout (MvD) was significantly associated with glaucoma and glaucoma progression. To understand the clinical relevance/importance of MvD, it is essential to know the exact vascular anatomy of optic nerve head (ONH). Although it is known that parapapillary choroid and the deep ONH structure including prelaminar tissue are both supplied by branches of short posterior ciliary artery, it remains controversial whether parapapillary choroid provides a major contribution to the prelaminar tissue perfusion. This study investigated perfusion within and around the ONH using indocyanine green angiography. Thirty-three eyes from 33 patients with primary open-angle glaucoma and 10 eyes from 10 normal subjects were included. The temporal sequence of dye appearance in various tissues was analyzed. We also sought the microvessels directly responsible for blood supply to the prelaminar tissue. The perfusion of the prelaminar tissue, which occurred in a sectoral fashion, was dependent on the dye appearance in the adjacent parapapillary choroid. In addition, microvessels crossing over the optic disc margin from the parapapillary choroid to the ONH were found. The findings suggest that the centripetal flow from the parapapillary choroid is an important source of prelaminar tissue perfusion.