Role of nitric oxide in the control of ocular blood flow

In the recent years it has been recognized that nitric oxide is an importan t regulator of ocular blood flow. Nitric oxide is involved in the control o f basal blood flow in the choroid, optic nerve and the retina. In addition, nitric oxide mediates a number of vasodilator responses in ocular vessels to agonists such as acetylcholine, bradykinin, histamine, substance P and i nsulin. Nitric oxide also plays a role in hypercapnia-induced vasodilation in the choroid and is a modulator of pressure autoregulation in this vascul ar bed. Abnormalities of the L-arginine/nitric oxide system have been obser ved in a variety of ocular diseases including glaucoma, diabetic retinopath y and retinopathy of prematurity. This makes the L-arginine/nitric oxide pa thway an attractive target for therapeutic interventions. Additional resear ch is required, particularly in characterizing the role of the three nitric oxide synthase isoforms in the control of ocular perfusion, to implement t his concept into the clinical management of ocular diseases. (C) 2001 Elsev ier Science Ltd. All rights reserved.