New concepts of regulation of retinal vessel tone.

OBJECTIVE: To review the mechanisms of local regulation of the vascular tone of the retinal and choroidal circulations.
DESIGN: Literature review.
RESULTS: The vascular endothelial cell may produce nitric oxide, endothelins, prostaglandins, and renin-angiotension products in response to chemical stimuli such as acetylcholine and bradykinin, to changes in blood pressure and vessel wall stress, to changes in local oxygen levels, and to other local stimuli. These substances are among the most potent vasoconstrictors and vasodilators known. Preliminary investigations suggest a potential role for these substances in endothelial autoregulation of the retinal and choroidal vasculatures.
CONCLUSION: Hormonal products of the vascular endothelium may provide the final common pathway for vessel autoregulation in response to varying physiologic stress in many vascular beds, including the retina and choroid. Pharmacologic modulation of this process may provide treatment modalities for diseases such as hypertensive and diabetic retinopathies.