-- card: 9071 from stack: in -- bmap block id: 9775 -- flags: 0000 -- background id: 2278 -- name: Blood Supply -- part 1 (button) -- low flags: 00 -- high flags: 2000 -- rect: left=246 top=324 right=336 bottom=258 -- title width / last selected line: 0 -- icon id / first selected line: 0 / 0 -- text alignment: 1 -- font id: 0 -- text size: 12 -- style flags: 0 -- line height: 16 -- part name: 1 ----- HyperTalk script ----- on mouseUp visual iris close go to card id 23421 end mouseUp -- part 2 (button) -- low flags: 00 -- high flags: 2000 -- rect: left=261 top=324 right=336 bottom=273 -- title width / last selected line: 0 -- icon id / first selected line: 0 / 0 -- text alignment: 1 -- font id: 0 -- text size: 12 -- style flags: 0 -- line height: 16 -- part name: 1 ----- HyperTalk script ----- on mouseUp visual iris close go to card id 23752 end mouseUp -- part 3 (button) -- low flags: 00 -- high flags: 2000 -- rect: left=277 top=324 right=336 bottom=289 -- title width / last selected line: 0 -- icon id / first selected line: 0 / 0 -- text alignment: 1 -- font id: 0 -- text size: 12 -- style flags: 0 -- line height: 16 -- part name: 1 ----- HyperTalk script ----- on mouseUp visual iris close go to card id 24045 end mouseUp -- part 4 (button) -- low flags: 00 -- high flags: 2000 -- rect: left=292 top=324 right=336 bottom=304 -- title width / last selected line: 0 -- icon id / first selected line: 0 / 0 -- text alignment: 1 -- font id: 0 -- text size: 12 -- style flags: 0 -- line height: 16 -- part name: 1 ----- HyperTalk script ----- on mouseUp visual iris close go to card id 24101 end mouseUp -- part 5 (button) -- low flags: 00 -- high flags: 2000 -- rect: left=307 top=324 right=336 bottom=319 -- title width / last selected line: 0 -- icon id / first selected line: 0 / 0 -- text alignment: 1 -- font id: 0 -- text size: 12 -- style flags: 0 -- line height: 16 -- part name: 1 ----- HyperTalk script ----- on mouseUp visual iris close go to card id 24384 end mouseUp -- part 6 (button) -- low flags: 00 -- high flags: 2000 -- rect: left=322 top=324 right=336 bottom=334 -- title width / last selected line: 0 -- icon id / first selected line: 0 / 0 -- text alignment: 1 -- font id: 0 -- text size: 12 -- style flags: 0 -- line height: 16 -- part name: 1 ----- HyperTalk script ----- on mouseUp visual iris close go to card id 27361 end mouseUp -- part 7 (button) -- low flags: 00 -- high flags: 2000 -- rect: left=337 top=325 right=337 bottom=349 -- title width / last selected line: 0 -- icon id / first selected line: 0 / 0 -- text alignment: 1 -- font id: 0 -- text size: 12 -- style flags: 0 -- line height: 16 -- part name: 1 ----- HyperTalk script ----- on mouseUp visual iris close go to card id 27620 end mouseUp -- part 8 (button) -- low flags: 00 -- high flags: 2000 -- rect: left=352 top=325 right=337 bottom=364 -- title width / last selected line: 0 -- icon id / first selected line: 0 / 0 -- text alignment: 1 -- font id: 0 -- text size: 12 -- style flags: 0 -- line height: 16 -- part name: 1 ----- HyperTalk script ----- on mouseUp visual iris close go to card id 27774 end mouseUp -- part contents for background part 1 ----- text ----- XII. Blood supply to the brain, eye, and orbit: A. Introduction: 1. Constant blood supply to brain and eye is required, CNS tissue has high metabolic rates, but cannot store energy, cannot use anaerobic metabolism, loss of blood supply (ischemia) causes nueronal death in minutes. 2. Vascular diseases: Interupted blood supply. a. Hypertension. b. Atherosclerosis: Hardening of the arteries. B. Vertebral blood supply to brain: 1. Aorta to subclavian to 2 vertebrals to basilar. 2. Vertebral arteries enter cranium through foramen magnum and combine into basilar. 3. Branches of basilar artery to brain. a. Posterior cerebral arteries: Serve LGN, visual cortex, posterior optic radiations, and superior colliculus. b. Superior cerebral arteries: Serves superior colliculus. (See diagram 1) C. Internal carotid supply to the brain: 1. (See diagram 2) 2. Branches of the internal carotid: Five of them. a. Anterior cerebral: One from each internal carotid, joined near chiasm by anterior communicating artery, serves chiasm and intracranial optic nerve. b. Ophthalmic: Supply to eye. c. Middle cerebral: Largest branch of the internal carotid, this artery is the most critical for stroke patients, serves chiasm, optic tract, optic radiations, visual cortex. d. Anterior choroidal: Serves chiasm, optic tract, LGN, beginnings of the optic radiations. e. Posterior communicating: Anastomoses of carotid and vertebral system. D. Circle of Willis: (See diagram 3) 1. Most brains do not have a complete circle of Willis. 2. The circle is completed by the anterior and posterior communicating arteries. 3. Provides alternative blood supply to brain: Vertebral and carotid. E. Venous return from brain: 1. Parallels arteries of brain. 2. Veins drain into sinuses: Venous channels formed by splitting of the dural lining of the skull. (See diagram 4) 3. Cavernous sinuses: a. Two sinuses on floor of skull, formed by the splitting of the dura matter, very large. b. Flows into jugular vein. c. Receives blood from ophthalmic vein. d. The internal carotid artery runs through the cavernous sinus from skull entry to branch point. e. Cranial nerves (III),(IV),(V),(maxillary and ophthalmic), and (VI) run through the walls of the cavernous sinus. f. Blockage of blood in the sinus puts pressure on the structures within the sinus. 1. Thrombus: Clot, puts pressure on structures. a. Less blood to brain from internal carotid. b. Paralysis of extraocular muscles (III,IV,VI). c. Loss of sensory input from (V),(maxillary and ophthalmic). F. Ophthalmic artery: Total blood supply to eye and orbit. 1. Characteristics: Coiled. a. Branch of internal carotid. b. Enters optic foramen with optic nerve. c. tortuous: For mobility of the eye, clotting at bends are dangerous. d. Parallel pair of veins leave orbit at orbital fissure (no valves). 2. Branches of the ophthalmic artery: a. Central retinal artery (CRA): 1. Branches off near optic foramen. 2. Runs below and close to optic nerve, enters 10 to12 mm. behind eyeball (half of the intraorbital distance of the optic nerve), runs through the center of the optic nerve, through the lamina cribrosa, right angle at surface of optic disc. 3. Branches in retina: Superior and inferior then nasal and temporal, loops back at ora serrata forming central retinal vein (CRV) at center of optic disc, leaves optic nerve 10 to12 mm. behind eyeball, drains into superior ophthalmic vein or cavernous sinus. 4. Use of ophthalmoscope: a. Arteries are brighter red. b. Arteries have a light streak in the middle (arterial light reflex). c. Arteries are usually smaller than veins. d. Capillaries from CRA do not supply foveola. e. No sphincters in retinal arterioles, flow is controlled in capillary beds to maintain blood oxygen levels. f. Near ora serrata the end arteries loop back to the venous system, degeneration of these end arteries with age cause peripheral cystoid degeneration. b. Short ciliary arteries: 8 to 18 of them branch from ophthalmic. 1. Enter through sclera in a ring around optic nerve. 2. Choroidal blood supply: Branch anterior and inner and form choriocapillaris. 3. Choriocapillaris: Haller's and Sattler's layer, wide-bore, fenestrated, serving outer retinal layers (PE cells, photoreceptors and foveola). 4. Some branches anastomse to form circle of Zinn, blood supply to optic disc. 5. Cilio-retinal artery: Can join choroidal and retinal blood supply usually from circle of Zinn, only present in about 15% of the population. c. Long posterior ciliary arteries: 1. Two branches, enter sclera at each side of optic nerve outside circle of short ciliary arteries. 2. Run through suprachoroid to anterior eye. 3. At anterior eye they divide into superior and inferior branches, all anastomose with anterior ciliary arteries to form major circle of iris, just inner to Muller's muscle of the ciliary body. 4. Major circle branches to radial arteries of iris and to most of the ciliary body. 5. Before formation of major circle there are recurrent branches to anterior choriocapillaris. 6. Drainage from choroid is non-parallel, four vortex veins in all four quadrants, the two superior vortex veins drain into the superior ophthalmic vein, the two inferior vortex veins drain into the inferior ophthalmic vein. d. Muscular arteries: 1. Wolff's description: Two large muscular arteries. a. Lateral: Branch of lacrimal artery, serves LR, SR, SO, and levator. b. Medial: Branch of ophthalmic artery, serves MR, IR, IO. 2. Alternative explainations: 4 muscular arteries. a. I.: Branch from lacrimal artery, serves LR. b. II.: Branch from supraorbital artery, serves SR, SO, levator through supraorbital foramen. c. III.: Branch from ophthalmic artery, serves MR. d. IV.: Branch from infraorbital artery, serves IR, IO, leaves through infraorbital foramen. e. Anterior ciliary arteries: 7 of them. 1. Branches from muscular arteries. 2. Reach eye along tendons of rectus muscles. 3. Pierce sclera and join major circle, then anastomose with long posterior ciliary arteries. 4. Before piercing sclera, branch anteriorly to make up episcleral plexus at limbus, limbal loops, and conjunctival plexus. 5. Also sends recurrent branches to choroid. f. Lacrimal artery: 1. A direct branch of the ophthalmic artery. 2. Lateral side of orbit. 3. Supplies LR, lacrimal gland, branches to connective tissue in optic nerve (pia), anterior to serve eyelid via lateral palpebral artery (3 arcades). 4. Supplies temple area via zygomatic artery. g. Supraorbital artery: 1. Branches off above optic nerve, goes above eye and muscles. 2. Serves forehead, SR, SO, levator, leaves orbit through supraorbital foramen. h. Anterior and posterior ethmoidal arteries: 1. Exits orbit through ethmoidal foramen, supplies ethmoid sinus and nose. i. Supratrochlear artery: 1. Exits orbit through septum orbitale. 2. Serves orbicularis, corrugator, and skin of forehead. j. Dorsal nasal artery: 1. Serves nasal mucosa, lacrimal sac, skin of nose. 2. Penetrates septum orbitale exiting orbit. k. Medial palpebral artery: Branch of dorsal nasal artery. 1. Three (3) branches or arcades to medial eyelid. 2. Also serves caruncle and plica semilunaris. (See diagram 5) (See diagram 6) Summary of ophthalmic artery: 1. Lateral side of orbit: Lacrimal artery. 2. Medial side of orbit: Direct branches from ophthalmic. 3. Upper side of orbit: Supraorbital artery. 4. Lower side of orbit: Infraorbital (not a part of the ophthalmic artery system). G. Venous drainage of the eye and orbit: 1. Superior ophthalmic vein: a. Receives blood from upper half of eye, orbit, and lids. 1. Superior vortex veins (2). 2. Superior muscular veins (two from the SR and MR, one from the LR, and one from SO). 3. Venous arcades from eyelids, some go to face. 4. Central retinal vein (CRV). b. Leaves orbit by superior orbital fissure to cavernous sinus. 2. Inferior ophthalmic vein: a. Receives blood from lower half of eye, orbit, and lids. 1. Inferior vortex veins (2). 2. Inferior muscular veins (one from IO, two from IR). 3. anterior ciliary veins: 14 of them. a. Two for each anterior ciliary artery. b. Fed from three sources: 1. Anterior ciliary plexus in anterior ciliary body. 2. Episcleral plexus, includes aqueous from Schlemm's canal. 3. Limbal loops. 4. These drain into the muscular veins. H. Summary of Circulation: 1. Retina: a. Inner: Central retinal artery and vein. b. Outer: Short posterior ciliary arteries (choriocapillaris). 2. Choroid: a. Primary: Short posterior ciliary arteries. b. Anterior secondary: Anterior ciliary arteries, long posterior ciliary arteries. 3. Iris: a. Major circle of the iris: Anterior ciliary arteries, long posterior ciliary arteries. 4. Lens: a. No blood supply, served by aqueous. 5. Conjunctiva and eyelids: a. Medial: Medial palpebral artery from ophthalmic. b. Lateral: Lateral palpebral artery from lacrimal. c. At limbus, conjunctiva: Anterior ciliary arteries. 6. Cornea at limbus: a. Anterior ciliary arteries. 7. Sclera: a. Avascular, some small branches of the long posterior ciliary arteries. 8. Extraocular muscles: a. SR and SO: Supraorbital artery. b. MR: ophthalmic artery. c. LR: Lacrimal artery. d. IR and IO: Infraorbital artery. I. Lymphatics: 1. No lymphatic system in the eyeball itself. 2. Eyelids and conjunctiva: a. Lateral: Preauricular lymph nodes. b. Medial: Submandibular lymph nodes. The circulation overall summarized: About three forths of the blood supply to the eye and orbit is supplied by the ophthalmic branch of the internal carotid artery. The remainder is supplied by a branch of the external carotid artery. Most of the veins draining the orbital area empty in to the cavernous sinus and the internal jugular vein. The rest drain into the pterygoid plexus and the external jugular vein. Extraocular structures: Most of the extraocular structures derive blood from the ophthalmic artery, a vessel which arises from the internal carotid artery. The ophthalmic artery enters the orbit through the optic foramen lateral to the optic nerve. Normally it passes over the nerve as it branches to supply the orbit and globe. Three main branches of the ophthalmic artery, the lacrimal, supraorbital, and medial branch, supply the lateral, upper and medial structures of the orbit, respectively. The lacrimal artery sends branches laterally and above to the lateral rectus and sometimes to the superior rectus muscles, to the lacrimal gland, and to both lids. A recurrent meningeal branch passes back through the superior orbital fissure to the brain. Branches from the supraorbital artery supply the superior rectus, the levator, and superior oblique muscles, the forehead and upper lid, and often the lacrimal gland. The true continuation of the ophthalmic artery is its medial branch which supplies the medial rectus muscle and may send branches to neighboring extraocular muscles. It gives off the frontal artery to the forehead and upper lid, as well as the dorsal nasal artery to the lids and lacrimal sac. The ethmoid arteries pass through the ethmoidal foramina and are not involved in the circulation of the eye. The lower portion of the orbit is supplied by the infraorbital artery. A continuation of the pterygopalatine branch from the internal maxillary and external carotid system, the infraorbital artery enters the orbit through the inferior orbital fissure. Branches of the inferior artery supply the inferior rectus and the inferior oblique muscles, the lower lid, the lacrimal sac and duct, and the lacrimal gland. The infraorbital artery then continues into the infraorbital canal. (See diagram 7) The veins of the orbit: The orbital contents are drained primarily by the superior and inferior ophthalmic veins. The larger superior ophthalmic vein drains those areas supplied by the branches of the ophthalmic artery, that is, the nasal, upper and temporal portions of the orbit. Thus it receives the veins from all of the extraocular muscles except the inferior rectus and inferior oblique. The superior ophthalmic vein leaves the orbit via the the superior orbital fissure and empties into the cavernous sinus which in turn drains into the internal jugular vein. A smaller vessel, the inferior ophthalmic vein drains the lower portion of the orbit. It originates with a network of veins at the front part of the floor and medial wall of the orbit and drains those areas supplied by the infraorbital artery, including the muscular veins of the inferior rectus and inferior oblique. The inferior ophthalmic vein usually leaves the orbit in two divisions. One branch descends through the inferior orbital fissure of the pterygoid plexus, with eventual drainage into the internal maxillary, internal jugular and external jugular veins. The other branch of the inferior ophthalmic vein usually passes through the superior orbital fissure joining the superior ophthalmic vein before it enters the cavernous sinus. The lids and conjunctiva: Circulation of the lids and conjunctiva is complex and varied and is derived from the vessels that supply the face, as well as those that supply the orbit. However, most of the palpebral blood supply derives from branches of the ophthalmic artery. Laterally the lacrimal artery supplies the lateral palpebral arteries to the upper and lower lids. Medially, the dorsal nasal artery from the ophthalmic, supplies the upper and lower medial palpebral arteries. These arteries join to form the palpebral arcades in the lids, the pattern being less distinct in the lower lid. The veins of the lids have a similar arcaic pattern. Medially they drain into the angular vein, then either to the superior ophthalmic vein through the orbital veins, or to the anterior facial vein. Laterally they empty into the anterior facial vein and superficial temporal vein. The palpebral arcades also supply most of the arteries to the conjunctiva, including the palpebral conjunctiva, the fornices, and the bulbar conjunctiva, up to four millimeters from the limbus. Most of the conjunctival veins drain into the veins of the upper and lower lids. Near the limbus though, the deeper veins drain to the anterior ciliary veins of the globe. Supply to the globe: The globe is supplied largely by the ophthalmic artery and its branches, which form two independent circulatory systems within the globe. The retinal system supplies the inner layers of the retina only and the choroidal or ciliary system supplies the rest of the globe. The retinal system consists of the central retinal vessels and their branches. The retinal artery is the first branch to arise from the ophthalmic artery at the apex of the orbit. It enters the optic nerve between 7 and 15 millimeters behind the globe accompanied temporally by the central retinal vein. The course of the vessels in the retina can easily be seen using an ophthalmoscope. The artery and vein immediately divide into upper and lower branches as they appear towards the nasal side of the optic disc. Fluorescein angiography clearly demonstrates further branching of these vessels to provide the blood supply to the entire retina. The arterial branches end in capillaries which do not anastomose with any other system of vessels. The pattern formed around the macula is similar to that formed by the nerves. The capillaries of the CRA do not anastomose with any other system of vessels upon leaving the globe. The CRV usually drains into the cavernous sinus with an anastomic branch to the superior ophthalmic vein, or rarely into the inferior ophthalmic vein. The retinal artery and vein serve all portions of the retina except a layer of rod and cone cells which are supplied by the choroidal circulation. The choroidal or ciliary circulation: The ciliary system supplies the choroid, the ciliary body, the iris, the cornea and the structures near the limbus. This circulation is composed of an anterior and a posterior system of arteries and veins which interconnect in the ciliary body (the major circle of the iris). The posterior ciliary arteries arise in a variable pattern from the ophthalmic artery and run parallel to the optic nerve toward the globe. Two long posterior ciliary arteries, temporal and nasal, and about 20 short posterior ciliary arteries are usually present. A few of the short arteries anastomose to form the circle of Zinn within the sclera around the optic nerve and supply the nerve head. Most of the short arteries pass into the globe where their many branches, along with those of the veins, comprise the choroid. The two long posterior ciliary arteries run in the sclera and suprachoroidal space directly to the ciliary body where each artery divides into a superior and inferior branch. These four branches anastomose in the anterior part of the ciliary body to form part of the great arterial circle (major circle of the iris). At this point the anterior ciliary arteries enter the eye to supply most of the anterior part of the globe. The seven anterior ciliary arteries spring from the arteries of the four rectus muscles at their insertions. The inferior, medial and superior rectus arteries supply two anterior ciliary arteries each, while the lateral rectus artery gives off one. The anterior ciliary arteries run in three general directions. Some of the smaller branches run forward toward the canal of Schlemn, the cornea and conjunctiva. Larger recurrent branches are sent backward to the ciliary muscle and to the choroid. Large branches also descend straight into the anterior part of the ciliary body. These straight branches join with the branches of the long posterior ciliary arteries in the arterial circle. The arterial circle lies just behind the base of the iris and supplies arteries to the iris which run radially toward the pupil. A few of these vessels divide before reaching the pupillary margin and form an incomplete ring known as the minor circle of the iris. The normal cornea does not contain blood vessels, but receives its supply from the capillaries derived from the anterior branches of the anterior ciliary arteries. The primary system of venous drainage from the uveal tract is the posterior or vortex system. From the iris and most of the ciliary body the vessels pass backwards to join the veins of the choroid. From the choroicapillaris to the outer portions of the choroid progressively larger vessels are formed which begin to assume circular or vortex configurations within the choroid. Four large vortex veins finally emerge, one from each quadrant of the choroid and leave the globe some five to eight millimeters behind the equator. The upper two vortex veins drain into the superior ophthalmic vein and the lower two drain into the inferior ophthalmic vein. The anterior ciliary system of veins drain the most anterior and outer portions of the globe, that is, the areas near the limbus. These areas include the anterior and outer portion of the ciliary body, the canal of Schlemn, and the cornea. The veins from the outer part of the ciliary body, or the anterior ciliary plexus, as well as twenty or more aqueous veins from the canal of Schlemn drain to an intrascleral veinous plexus which in turn drains into the episcleral plexus. At the corneal limbus the capillary arteries that supply the cornea bend backwards forming the limbal loops at which point they become the corneal veins which drain directly into the episcleral plexus. From the episcleral plexus, the anterior ciliary veins (about 14 in all) run to the insertion of the rectus muscles to drain into the muscular veins. The anterior ciliary veins thus follow the same pattern as the anterior ciliary arteries except that the veins are twice as numerous. The veins from the inferior rectus and inferior oblique muscles then join the inferior ophthalmic vein. Blood from the rest of the muscular veins drains into the superior ophthalmic vein and flows through the cavernous sinus and into the internal jugular vein. (See diagram 8)