NPY and glaucoma: Abnormal neuro-metabolic-endothelial mechanisms of the vascular tone control in glaucoma patients is related to the effects of vasoactive factors—endothelin–1 (ET-1), neuropeptide Y (NPY), nitric oxide (NO), prostacyclin (PGI 2), tumor necrosis factor (TNF-alpha), cyclooxygenase (COX-2), and metalloproteinases (MMP-9).