Retinal circulation

Retrobulbar hemorrhages During the administration of botulinum toxin type A for the treatment of strabismus, retrobulbar hemorrhages sufficient to compromise retinal circulation have occurred from needle penetrations into the orbit. It is recommended that appropriate instruments to decompress the orbit be accessible. Ocular (globe) penetrations by needles have also occurred. An ophthalmoscope to diagnose this condition should be available. Inducing paralysis in 1 or more extraocular P.788... 

Grunwald JE, Mathur S, DuPont J. Effects of dorzolamide hydrochloride 2% on the retinal circulation. Acta Ophthalmol Scand 1997 75 236-238. 

Tablets of medication intended for oral use contain inert filler materials such as talc (magnesium silicate), corn starch, cotton fibers, and other refractile and nonrefractile substances. Long-term drug abusers are known to prepare a suspension of medication for injection by dissolving the crushed tablet of cocaine, heroin, methylphenidate, or other narcotic in water. They then boil the solution and filter it through a crude cigarette or cotton filter before injecting the solution intravenously, subcutaneously, or intramuscularly. The talc particles eventually embolize to the retinal circulation and produce a characteristic form of retinopathy.

Blood is supplied to the retina by the central retinal artery and choroidal blood vessels (Oyster, 1999). The central retinal artery arises from the ophthalmic artery, w hich in turn branches off the internal carotid artery. Upon entering the retina, the central retinal artery branches into deep capillary beds in the INL and superficial capillary beds in the GCL. Endothelial cells of retinal capillaries are joined by tight junctions, contributing to the blood/retinal barrier. There is litde or no autonomic regulation of the retinal circulation blood flow through these capillaries is instead primarily controlled by autoregulation (Wangsa-Wirawan and Linsenmeier, 2003). Retinal capillaries drain into the central retinal vein. 

Topical fluorescein dye is often used during slit lamp examination, because it helps in identifying corneal epithelial defects (1). Fluorescein retinal angiography was first described in 1961 (2) rapid intravenous injection of fluorescein displays retinal circulation velocity and the fine architecture and integrity of the blood retinal barrier. This is associated with minor adverse events in 21% of cases and potential life-threatening adverse events in 0.5% (3). 

Fluorescein structural formula and molecular model. This strongly fluorescent dye has many applications. It is widely used to study retinal circulation and various diseases involving the retina. The technique is known as fluoi escein angiography. Fluorescein can be bound to DNA and other proteins and its fluorescence used as a probe of these molecules and their interactions. Fluorescein is also used for water tracing to provide information on the contamination of underground wells. In addition, it has been used as a laser dye. 

Hickam JB, Frayser R. Studies of the retinal circulation in man observations on vessel diameter, arteriovenous oxygen difference, and mean circulation time. Circulation 1966 33 302-316. 

Shiba T, Inoguchi T, Sportsman JR, Heath WF, Bursell S, King GL. Correlation of diacylglycerol level and protein kinase C activity in rat retina to retinal circulation. Am J Physiol 1993 265 E783-E793. 

Michaelson JC. Retinal circulation in man and animals (Thomas, Springfield, Illinois, 1954) 1-146. 

Hardy P, Beauchamp M, Sennlaub F, Gobeil F Jr, Tremblay L, Mwaikambo B, Lachapelle P, Chemtob S (2005) New insights into the retinal circulation inflammatory lipid mediators in ischemic retinopathy. Prostaglandins Leukot Essent Fatty Acids 72 301-325... 

A 74-year-old man developed orbital bleeding with chemosis, acute proptosis, and peribulbar hemorrhage after peribulbar anesthesia with 6 ml of lidocaine 2%, bupivacaine 0.75%, and 75 units of hyaluronidase without adrenaline. After ocular massage, compression with a Honan balloon was maintained at 30mmHg for 10 minutes, and the intraocular pressure normalized. Immediately after surgery the retinal circulation did not reperfuse, but on the first postoperative day the retinal vessels were perfused and the fundus looked normal. 

The study has produced detailed global and local information of hemodynamics of the mouse retinal circulation. Such information is only obtainable using an anatomical model such as that used in this study. 

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