Thursday, March 10, 2011

Retinal Circulation

The retinal circulation derives its circulation from the central retinal artery, which is a branch of the ophthalmic artery, but passing in conjunction with the optic nerve. This artery runs inferior to the optic nerve within its dural sheath to the eyeball. To provide retinal circulation, the central retinal artery pierces the optic nerve close to the eyeball, sending branches over the internal surface of the retina, and these terminal branches are the only blood supply to the larger part of it. They are branching in a segmental distribution to the end arterioles and not anastomoses. This is clinically significant for diseases affecting choroidal blood supply. The macula and the fovea responsible for central vision and the anterior part of the optic nerve are supplied by the choroid and not by central retinal artery.

Effect of Systemic Administration of Simvastatin on Retinal Circulation

Taiji Nagaoka, MD, PhD; Atsushi Takahashi, MD; Eiichi Sato, MD, PhD; Naohiro Izumi, MD; Travis W. Hein, PhD; Lih Kuo, PhD; Akitoshi Yoshida, MD, PhD

The objective of this research was to investigate the effect of systemic administration of simvastatin on the retinal circulation.

Methods  The effects of systemic administration of simvastatin on the retinal circulation after 90 minutes and after 7 days were studied in a placebo-controlled, double-masked, clinical trial among 12 healthy men. We used laser Doppler velocimetry to measure vessel diameter and blood velocity and calculated the blood flow in retinal arteries and veins. We also measured the intraocular pressure and the plasma nitrite/nitrate levels, the stable end products of nitric oxide metabolism.

Results  There were no significant changes in any retinal circulatory parameters at 90 minutes after administration of simvastatin. Daily administration of simvastatin for 7 days significantly increased blood velocity and blood flow in retinal arteries and veins but did not significantly change vessel diameter. The intraocular pressure significantly decreased at 90 minutes and at 7 days after administration of simvastatin. Simvastatin also significantly increased the plasma nitrite/nitrate levels.

Conclusion  Simvastatin induced an increase in blood velocity and blood flow in retinal arteries and veins, increased the plasma nitrite/nitrate levels, and decreased the intraocular pressure, probably through the increase in nitric oxide.