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Dr Dipali Chavan In human,the eyes have two separate systems of blood vessels which differ anatomically and physiologically. These are:1.Retinal vessels: supplying retina 2.Uveal or ciliary vessels: rest of eye Both the systems arise from ophthalmic artery, br.of internal carotid artery. Both the systems of vessels are derived from PERIOCULAR MESENCHYME derived from NEURAL CREST and associated paraxial mesoderm. Development of vasculature starts from a very early period of 5wks and continues even after birth. The orbital contents arc supplied chiefly by the internal carotid artery via its ophthalmic branch and, to a minor extent, by the external carotid artery via the infraorbital artery Venous drainage is via the Ophthalmic veins and tributaries, mainly into the cavernous sinus, but also into the facial veins. ARTERIES-foll.ones Ophthtalmic artery Cerebral arteries Circle of willis External carotid artery VENOUS DRAINAGE- goes into Superior ophthalmic vein Inferior ophthalmic vein Middle ophthalmic vein Medial ophthalmic vein Angular vein Cavernous sinus The artery is described in three parts: 1. intracranial; 2. intracanalicular; 3. intraorbital. Ophthalmic artery Main source for the ocular structures. Branch of ICA Intracranial part : At its origin,is medial to ant. Clinoid process and inf.to optic nerve. intracanalicular part: after its origin ,the ophthalmic artery passes through the optic canal within the dural sheath of optic nerve , lying inferior to it. Intraorbital part :At the apex of the orbit in the muscle cone , the artery pierces the dural sheath of the optic nerve and comes to lie lateral to the optic nerve and medial to the Oculomotor and Abducent nerves. At this point ,ciliary ganglion lies between the Ophthalmic artery and lateral rectus muscle. Intraorbital part (CONTD): Then the artery moves forwards and upwards and crosses over the optic nerve and below the superior rectus muscle and comes to lie on the medial side of optic nerve. Here it is accompanied by the nasocilliary nerve and the superior ophthalmic vein (in 10-15 % cases artery passes below the optic nerve.)then it moves forward between medial rectus and superior oblique muscle towards the maxillary process of the frontal bone. The terminal part of artery enters the peripheral surgical space of the orbit . Ends at medial end of upper eyelid by dividing into two terminal branches, namely dorsal nasal artery and supratrochlear artery. The usual order of appearance of branches of this artery is: 1. central retinal; 2. medial and lateral posterior ciliary; 3. lacrimal (and lateral palpebral); 4. recurrent meningeal; 5. muscular (and anterior ciliary); 6. posterior ethmoidal; 7. supraorbital; 8. anterior ethmoidal; 9. medial palpebral; 10. collaterals to optic nerve sheath; 11. periosteal; 12. dorsal nasal (terminal); 13. supratrochlear (terminal). CENTRAL RETINAL ARTERY:arises near the optic foramen and courses ahead with 5-6 right angle bends as followsOutside optic nerve- it runs a wavy course forward, below the optic nerve, but adherent to the dural sheath to about 1015mm behind the eyeball, where at a point along the inferomedial aspect of nerve it bends upwards to pierces the dura and arachnoid ,from both of which it receives covering. In the subarachnoid space- it bends forwards and after a short course it again bends upwards at nearly right angle & invaginates the pia to reach the centre of the nerve. the entering vessel is thus clothed by pia along with the pial vessels. it is also surrounded by a sympathetic nerve plexus (N of tiedemann). In the centre of optic nerve- the artery bends forwards and then in company with the vein, which lies on its temporal side, it passes anteriorly and pierces the lamina cribrosa to appear inside the eye. In the optic nerve head- it lies superficially in the nasal part of physiological cup, covered only by that layer of glial tissue(connective tissue meniscus of kuhnt)which closes the physiological cup. here it divides into two br-sup & inf ,each further subdivides into temporal and a nasal br at or near the margin of the optic disc. In the retina- 4 terminal br of CRA namely, sup nasal, sup temporal, inf nasal & inf temporal divide dichotomously as they proceed towards the ora serrata, where they end without anastomosis. Abbreviations: A = arachnoid; C = choroid; CRA = central retinal artery; Col. Br. = Collateral branches; CRV = central retinal vein; D = dura; LC = lamina cribrosa; NFL = surface nerve fiber layer of the disc; OD = optic disc; ON = optic nerve; P = pia; PCA = posterior ciliary artery; PR and PLR = prelaminar region; R = retina; RA = retinal arteriole; S = sclera; SAS = subarachnoid space. Recurrent meningeal artery : This artery passes through the superior orbital fissure. It anastomoses with the middle meningeal artery ,which is a branch of external carotid artery .thus ,this anastomoses is between the internal and external carotid arteries. Long and short posterior cilliary arteries. -These arteries arise from the Ophthalmic artery below the optic nerve., later divide into 10-20 branches . -These branches run forwards, surround the optic nerve and pierce the eyeball close to it. - Most branches, the short ciliary arteries, enter the choroid. Two long posterior ciliary arteries pierce the sclera medial and lateral to the nerve and pass between the sclera and choroid to supply the ciliary body, anastomosing with anterior ciliary arteries to form the circulus arteriosus iridis major, supplying the iris. Muscular branches: The muscular arteries are subdivided into three groups: the superior artery, supplies the superior and lateral recti, levator and superior oblique (Hayreh, 1962). The inferior artery, present in 98% of specimens, is the largest branch on the orbital floor, supplies the inferior and medial recti, inferior oblique and sometimes the lateral rectus (Hayreh, 1962). A variable number of independent vessels arise from the main artery and also from the lacrimal and supraorbital. The muscular arteries of the recti run forward with in their tendons and pierce the sclera to anastomose with posterior ciliary arteries. Their anterior ciliary rami pass forward in the episclera to supply the subconjunctival, marginal corneal and perilimbal conjunctival networks Lacrimal artery: At the upper border of lateral rectus it supply the lacrimal gland. It traverses the gland and supplies the eyelids and the conjunctiva through its lateral palpebral branches and forms superior and inferior anastomotic arcades with the medial palpebral arteries Anterior cilliary arteries: Branches of the muscular arteries. Seven in number ,two of each from sup rectus, inferior rectus,medial rectus ,one branch from the lateral rectus. These artery give off ant.conj.art.just before piercing the sclera at about 4mm from the limbus. These anastomose with the long posterior ciliary arteries and supply ciliary body and iris. supraorbital artery: Passes through the supraorbital notch, supplies the upper eyelid and scalp. ARTERIES OF BRAIN INTERNAL CAROTID ARTERYEnters the middle cranial fossa by passing through carotid canal. It runs in the cavernous sinus and emerges in the anterior part of roof. Lies lat.to optic chiasma and terminates by dividing into ant. & middle cerebral art. The internal carotid artery gives off caroticotympanic and pterygoid branches in its petrous part and cavernous, hypophyseal and meningeal branches in its cavernous part. Has foll.branches of cerebral part-Ophth.art.,Post.comm.A,Choroidal art.,ant. & middle cerebral art(largest branch). VERTEBRAL ARTERYEnters the post.cranial fossa by passing through foramen magnum and unite with each other at the lower border of pons to form basilar artery which in turn ultimately divides into two post.cerebral arteries. CIRCLE OF WILLIS Lies in interpeduncular fossa at the base of brain. Formed by-ant.comm.artery,ant.cerebral artery ,ICA,post.cerebral artery,post.comm.art, and the basilar art. Thus basically a free anastomoses between ICA & Vertebral A. Equalizes pressure on the arteries of two sides. EXTERNAL CAROTID ARTERY Branch of common carotid artery. Passes upwards through the tissues of neck. Major branches which supply ocular adnexa are- -Superficial Temporal A,Maxillary A,angular art, infraorbital art, Transverse Facial A, Zygomatic art. Superior ophthalmic vein(SOV): Starts by joining of its superior and inferior roots in the superomedial part of ant.orbit. In the orbit,it accompanies ophthalmic artery and lies above the optic nv. Joins IOV near the sup.orbital fissure and finally terminates in the cavernous sinus. Tribu.are-angular v, supraorbital v, lacrimal v, Central Retinal V, Inferior Ophthalmic V, ant.ciliary v and two upper vorticose veins. Inferior ophthalmic vein(IOV): commences from inferior venous network near the ant. part of floor of orbit. Terminates in the cavernous sinus either directly or by joining SOV. Receives trib.from- LL,lower and lat.ocular ms, conjunctiva ,lac.sac, & lower two vorticose veins. Middle ophthalmic vein: Arises near the inf.margin of lat.rectus ms. Drains the inf.venous network and ultimately joins the confluence of Sup. Ophthalmic V in the cavernous sinus. Some considered it as 2nd Inf Ophthalmic V. Seen in about 20% of individuals. Medial ophthalmic vein: Arises either from the inf. root or from ant.part of the SOV. Ultimately drains into cavernous sinus. Present in about 40% of individuals. Angular vein: Formed by the union of supraorbital and supratrochlear v. Lies lat.to angular art. And is situ.8mm medial to medial canthus. Below continues as the facial vein. Imp.landmark during the lac.sac surgery. Trib.are-Supra Orbi.V,Supra Troch.V,,Sup. and inf. Superficial palpebral v, and superficial nasal br. Cavernous sinus: It is a large venous space situ. in the middle cranial fossa, one on either side of body of the sphenoid bone. Tributaries are SOV,IOV or its branch, medial oph. v, central retinal v., veins from brain( sup middle cerebral vein ,inf cerebral vein) and from the meninges (middle meningeal vein). Draining channels Transvrse s(through the sup petrosal sinus) , Internal jugular V(inf petrosal sinus), pterygoid plexus of veins(through the emissary v), and into the opp. sinus. As cavernous sinus communicates to SOV & IOV,so infections from the areas drained by these veins can pass to cavernous sinus and vice-versa. CHOROIDAL VESSELS Acc.to Hayreh, post.ciliary arteries,choriocapillaries as well as the vortex veins have a segmental distribution in the choroid. they are also more or less end arteries. Layers-3 stratified layers Outermost-large venules Middle-smaller venules and arterioles. Innermost-choriocapillarie CHOROIDAL ARTERIES Intima consists of endothelium,basement mb., and int.elastic lamina. Media-single continuous layer of smooth ms.cells which contains abundant myofilaments. Adventitia-collagen fibre bundles,scattered elastic fibres and occasional fibroblasts. CHOROIDAL ARTERIOLES Foll.variations from arteries Internal elastic mb.absent Muscle layer becomes discontinuous and more circumferentially arranged. Amt.of collagen in the adventitia is considearbly diminished. CHOROIDAL VEINS AND VENULES Veins vary in dia.from 50-150u and consists of endothelium, basement mb., one or two layers of smooth muscles and a relatively thick collagenous adventitia. Venules are<40u.intima same as veins, but media contains a discontinuous layer of longitudinally arranged pericytes. CHORIOCAPILLARIES Large dia.8-40u. Vessel wall consists of fenestrated endothelium,surr.by a membrane. fenestrations are 700-800A’ in dia. and are covered by a diaphragm. Highly permeable to large molecules.so play an imp.role in adequate supply of vit.A to the pigmented epithelium of the retina. BLOOD VESSELS OF IRIS Arterial supply mainly from major arterial circle.radial arteries which supply the iris are basically arterioles. Major charac. histo. feature is a well developed and modified adventitia. innermost layer consists of longitudinal loosely arranged collagen fibrils enmeshed in an amorphous ground substance. outermost layer consists of densely packed circular collagen fibres. Radial veins are technically pericytic venules(collecting venules). Capillaries have a continuous non-fenestrated endothelium.low permeability of iridial capillaries and venules form a part of functional blood-aqueous barrier. Blood flow in retinal vessels is laminar with some pulsatile component. Blood flow in iris vessels is also laminar. Blood flow in choroidal vessels is controversial owing to cavernous structure of choriocapillaries-it is supposed that choroidal flow is mostly laminar with geographical filling of the separate choroidal segments. =retinal vsls receive about 5%of total ocular blood flow. =choroid about 65 to 85%,iris & ciliary body about 10 to 35% of ocular blood flow. Ocular blood flow is regulated by local as well as systemic regulatory mechanisms. Main factors influencing it are: -pressure head -autoregulation -resistance to the blood vessels -viscocity of the blood .main site of resistance is arterioles .it is regulated by neural mechanisms and chemical mediators. Blood flow in choroid and retinal vessels is steady and not alternating as the precapillary sphincters are absent here. PERFUSION PRESSURE : (MAP-IOP) -Either a fall in MAP or a rise in IOP should lower the PP and thus also the blood flow. - It mainly affects the blood flow in choroidal vessels not in retinal or ciliary vessels (presence of autoregulation in these vessels). AUTOREGULATION:it is a property of vascular bed that permits nearly constant blood flow over a wide range of perfusion pressure. -retinal vessels exhibit such a phenomenon. -two theories for this: a)myogenic theory b)metabolic theory NERVOUS CONTROL: Influences only choroidal vs,not the retinal ones. Effect of sympathetic supply: assists autoregulatory mech.& maintain the intraocular blood flow and volume constant.both the ciliary as well as extraocular part of CRA are under its control. Effect of parasympathetic supply : exists in ciliary processes and the choroid.These increase the blood flow when required by causing vasodilatation in the whole uvea,most marked in the choroid. CHEMICAL CONTROL: HYPERCARBIA causes marked vasodilatation of the uveal ts & increases the total blood volume in eye,resulting in rise in IOP. While the inhalation of 100% o2 causes slight vasoconstriction of retinal vs.inhalation of 7% co2 & 21% o2 cause moderate dilation of visible retinal vessels. DRUGS: drugs like papaverine,caffeine causes vasodilatation while ergotamine causes vasoconstriction,but NE increases blood flow inspite of its vasoconstricting effect. From anterior to posterior diff.parts of eye areo Eye Abrows and the eyelids o Cornea o Conjuctiva o Lacrimal glands and the lacrimal passages o Extraocular muscles o Sclera o Uveal tissues o Lens o Vitreous o Retina o The visual pathway EYEBROWS: Arterial supply- derived from supraorbital and superficial temporal a. Venous drainage:- supraorbital, frontal, angular and superficial temporal veins. EYELIDS: Arterial supply: Mainly supplied by medial and lateral palpebral A(the branches of dorsal nasal and lacrimal art.) The sup. And inf.art. enter the upper and lower eyelids by piercing through septum orbitale above and below the medial palpebral lig.,respectively. Each medial palpebral A. then anastomoses with the corresponding lat.palpebral a, to form marginal arterial arcade,which lies in submuscular plane in front of tarsal plate some 2-3mm away from lid margin,in each eyelid. In the upper eyelid,another arcade sup.or peripheral arterial arcade,is formed from the sup.branches of med.palpebral a,which lies near the upper border of tarsal plate. Branches from the arterial arcades go forward to supply orbicularis and skin & backward to supply tarsal glands & conjuctiva. Venous drainage: Veins are larger and more numerous than the arteries of the eyelids. Arranged on two sets of venous plexus in each eyelid: Pretarsal ven.plexusDrains structures superficial to tarsus. On medial side,drain into subcutaneous veins mainly the angular veinultimately drains into internal jugular vein. Post-tarsal ven.plexus: Drains structures posterior to the tarsal plate. Ultimately drains into the ophthalmic veins. CONJUCTIVA: Arterial supply-derived from three sources Marginal arcade of eyelid The peripheral arterial arcade The anterior ciliary arteries. palpebral conjuctiva and fornices are supplied by br.from marginal and peripheral arcades of eyelids.And the bulbar conj.is supplied by post.conj.art.and ant.conj.art. Venous drainage: The veins from the conjuctiva drain into the venous plexus of eyelids-drain into the sup.or the inferior ophthalmic veins. A circumcorneal zone of veins about 5-6mm from the limbus drain into the ant.ciliary veins. CORNEA: It is an avascular structure. Small twigs of vessels derived from the anterior ciliary vessels invade its periphery for about 1mm and provide nourishment. Actually these loops are not in the cornea,but in the subconjuctival tissue which overlaps the cornea. Relative avascularity is responsible for its transparency. Progressive vascularization is a harmful process as it interferes with its functional properties, especially its transparency. LACRIMAL GLANDS AND THE LACRIMAL PASSAGES: LACRIMAL GLAND Arterial supply- Main lacrimal gland is supplied by lacrimal artery,a br.of ophthalmic artery. Sometimes a br.of transverse facial artery may also supply the gland. Venous drainage Gland is drained by lacrimal veins --the ophthalmic vein. LACRIMAL PASSAGES Arterial supply derived from superior and inferior palpebral art(br.of ophthalmic artery),angular art,infraorbital artery and nasal br.of sphenopalatine artery. Venous drainage occurs into the angular vein and the infraorbital vein from above and into the nasal vein from below. EXTRAOCULAR MUSCLE: Arterial supply Usually two branches of the ophthalmic artery,namely medial and lateral muscular branches,supply the extra ocular ms. Medial ms br-larger of the two. Supplies the MR,IR and IO ms. Medial rectus also receives a br.from the lacrimal artery and the inferior rectus and oblique ms receive br.from the infraorbital artery. Lateral ms br-supplies the LR,SR,SO and the LPS ms. These muscular branches give rise to anterior ciliary arteries. Venous drainage Veins from the EOM correspond to the arteries and empty into the superior and inferior ophthalmic veins. SCLERA: Relatively avascular structure. However,anterior to insertion of the recti muscles,anterior ciliary artery form a dense episcleral plexus. Posterior part of the sclera receives small branch from the long and short posterior ciliary arteries. UVEAL TISSUE: Arterial supply supplied by 3 sets of arteries- Short posterior ciliary arteries- -arise as two trunks from ophthalmic artery. -Each trunk further divides into 10-20 br.which pierce the sclera around the optic nerve and supplied the choroid in the segmental manner. Long posterior ciliary arteries- -2 in no.(nasal and temporal),pierce the sclera obliquely on medial and lateral side of the optic nerve and run forward in the suprachoroidal space to reach the ciliary muscle,without giving any branch.at the anterior end of ciliary muscle. -these anastomose with each other and with the anterior ciliary arteries to form the major arterial circle and also give branches which supply the ciliary body. CONTD… Anterior ciliary arteries- deri.from muscular branches of ophthalmic artery. -several branches arises from the circulus arteriosus major plexus and supply the ciliary processes(one br.for each process). -similarly many br.from it run radially through the iris towards pupillary margin where they anastomose with each other to form circulus arteriosus minor. Venous drainage- veins draining uveal blood are Anterior ciliary veins- these are tributaries of the muscular veins. Since they carry blood only from the ciliary muscle,they are smaller than the corresponding arteries. Smaller veins from the sclera-these correspond to the scleral branches of short ciliary arteries.they only carry blood from the sclera and not from the choroid and are, therefore ,smaller than the corresponding arteries. The venae verticosae(vortex veins or posterior ciliary veins)-Usually 4 in no.(sup & inf temporal,and sup & inf nasal),pierces the sclera obliquely on each side of SR & IR,6mm behind the equator of the globe. -Of these STV is most posterior(8mm behind equator) and ITV is the most anterior(5.5mm behind the equator.they have an ampullary dilatation at their choroidal end. These veins drain blood from- -whole of choroid,receive small veins from optic nerve head,smtimes small v from retina.anterior tributaries come from the iris,ciliary processes,ciliary muscle and ant.part of choroid. -there is no major venous circle corresponding to major arterial circle. -these all 4 veins converge towards the apex of orbit d/t oblique arrangement of scleral canals.two sup.vortex veins open into sup.ophthalmic v directly or through its muscular or lacrimal tributaries.two inf.vortex veins open into the inf.ophthalmic veins. BLOOD SUPPLY OF RETINA diff.parts are supplied by diff.arteries Outer 4 layers of the retina viz.RPE,layer of rods and cones , ELM & ONL get their nutrition from choriocapillaries. Inner 6 layers ie OPL,INL,IPL,GCL,NFL & ILM get their supply from central retinal artery. OPL gets its blood supply partly from CRA and partly from choriocapillaries by diffusion. The fovea is an avascular area mainly supplied by choriocapillaries. The macular region gets its blood supply by small twigs from the sup.& inf. temporal br.of CRA. sometimes cilio-retinal artery(a br from ciliary system of vessels)is seen originating in a hook shaped manner within the temporal margin of the disc. it runs towards the macula and supplies it, thus when present, It helps to retain the central vision in the event of occlusion of CRA. THE RETINAL VESSELS ARE END ARTERIES.ie they do not anastomose with each other.h owever,anstomoses between the retinal vessels and ciliary system of vessels does exist(in the neighbourhood of lamina cribrosa)with the vessels which enter the optic nerve head from arterial system of zinn or haller. The terminal fundus arterioles bend sharply and dip almost vertically into the retina,forming the capillary network arranged as follows In most of the extramacular fundus,there are 2 retinal capillary networks- a superficial and a deep. The superficial network lies at the level of NFL and deep network lies b/n INL & OPL. deep network is more dense and complex than superficial. There are anastomotic capillaries which run from one to another. peripherally,as the ora serrata is approached, capillary network is reduced to a scanty single layer. In the parafoveal zone-capillary network is especially well developed and is three layered. however, there exists a capillary-free zone in the fovea, k/n as FOVEAL AVASCULAR ZONE(FAZ)of about 500um in diameter. In the peripapillary region,the capillary network becomes 4-layered to support the extremely thick nv fibre layer characteristic of this region. BLOOD SUPPLY OF THE VISUAL PATHWAY The visual pathway receives its blood supply from the two arterial systems,carotid and the vertebral,connected to each other at the base of brain by the arterial circle of willis. SIMILAR TO BRAIN, visual pathway is mainly supplied by pial network of vs except the orbital part of optic nv which is also supplied by an axial system deri.from CRA. Optic nerve: Intraocular (1mm) Intraorbital(30 mm) Intracanalicular(6-9mm) Intracranial (10 mm) Arterial supply : Mainly by posterior cilliary artery except for nerve fiber layer – which is supplied by retinal circulation. Nerve fibre layer is mainly supplied by arterial branches of central retinal artery. prelamilar and lamilar region is supplied by posterior cilliary arteries. Retrolamilar region supplied by both cilliary and retinal circulation. Anastomosis between retinal vessels and cilliary system of vessels does exit. Arterial anastomosis between 2-4 or more short posterior cilliary arteries,which lies in sclera around optic nerve called circle of zinn-haller Venous drainage: Mainly by central retinal vein Central retinal vein is tributary of superior ophthalmic vein ,it wil terminate in cavernous sinus. Small portion by choroidal system Intraorbital part by 2 system of vessels- periaxial and an axial. -periaxial system of vs supplying this part of optic nv is derived from 6 br of ICA namely Ophthalmic A,Long Posterior Ciliary A,Short Posterior Ciliary A,Lacrimal A & CRA before it enters optic nv and circle of zinn. -axial system of vs supplying axial part of optic nv is derived from-intraneural br of CRA, central collateral arteries which comes from CRA before it pierces the nv. & central artery of optic nv. The capillary network for the optic nv is derived from both the systems. Intracanalicular part- -supplied only by the periaxial system of vessels. -the pial plexus in this part is fed mainly by the br from the ophthalmic artery. Intracranial part Arterial supply this part is exclusively supplied from the periaxial system of vs. the pial plexus here is contributed by 4 sources- -br from ICA either directly or through recurrent br of Anterior Superior Hypophyseal A(supply inf aspect of optic nv containing lower retinal fibres);br from Anterior Cerebral A(supply sup aspect of optic nv containing upper retinal fibres);small recurrent br from Ophthalmic A and small twigs from Anterior comm. A . Venous drainage- the venous drainage in the optic nv head is primarily by CRV. Orbital part is drained by peripheral pial plexus and also by CRV in the distal part. Intracranial part is drained by pial plexus which ends in ant.cerebral and basal vein. BLOOD SUPPLY OF OPTIC CHIASMA Arterial supply- Vessels may enter directly or indirectly through the pial plexus. Main supply from branches of ant.cerebral and Int Carotid A with some contributions from others as follows Ant.cerebral and ant.commu.art-superior aspect Branches from ICA,Ant Sup Hypphyseal A and Post.commu.ainferior aspect Antero-inferior margin of chiasma-by the br.of ophthal.art. Venous drainage Sup.aspect-drained by-sup.chiasmal vein-ant.cerebral v Inf.aspect-by pre-infundibular v-basal vein Arterial supply Pial plexus supplying optic tract receives contribution from Post.commu.artery,ant.choroidal art.and branches from middle cerebral artery. Though no anastomosis but considerable overlap b/n ant.choroidal art.,and the branches of MCA.so no hemianopia d/t occlusion of ant chroidal A. Venous drainage Sup. Aspect-Ant.cerebral vein Inf. Aspect-Basal vein Arterial supply- Post.cerebral artery-postero-medial aspect-thus nourishes the fibres coming from the sup.homonymous quadrants of the retina. Anterior choroidal artery-solely the anterolateral aspectfibres coming from inf.homonymous quadrants of retina. Region of hilum-which contains macular fibres-by the rich anastomosis from both the posterior cerebral and the anterior choroidal arteries. Venous drainage- Basal vein Arterial supply Anterior choroidal artery-through the perforating branches-optic radiations anteriorly over the roof of inferior horn of lateral ventricle. Deep optic artery{br.of MCA}-middle part when they lie lateral to descending horn of lateral ventricle. Calcarine branches of Post Cerebral A and perforating branches from Middle Cerebral A-posterior part as the fibres spread out to reach the visual cortex. Venous drainage- -by the Basal vein and in some part by middle cerebral vein Arterial supply Mainly supplied by posterior cerebral artery-via calcarine artery supplemented by its other two branches-posterior temporal and parieto-occipital arteries.hence macula is spared in the event of calcarine art.occlusion. The terminal branches of MCA supply the anterior end of calcarine sulcus and lateral aspect of the occipital pole. At the posterior pole,rich anastomosis present b/n the MCA and PCA. Venous drainage Medial aspect-Internal occipital vein –great cerebal v of Galen and Straight sinus. Superolateral aspect-inferior cerebral v-cavernous sinus Orge, et. al. have shown that detachment of rectus muscles can reduce blood flow in the ophthalmic artery 30%, presumably because of ‘downstream’ effects. Such a change in susceptible individuals could lead to acute anterior segment ischemia. In clinical practice, it is not known with certainty what factors ultimately influence the postsurgical dynamics of anterior segment circulation in a given case. Some useful guidelines follow: When a muscle is detached and reattached, anterior ciliary vessels do not recannulate. Because there are no long posterior ciliary arteries superiorly or inferiorly, detachment of the superior or inferior rectus muscles disrupts iris vessel filling more than detachment of the horizontal recti. Older, vascularly-compromised patients may be more likely than young, healthy patients to develop anterior segment changes after eye muscle surgery. Iris angiography is a valid way to assess anterior segment circulation at a given time, but it is not a valid or practical predictor to determine what might happen if eye muscles are detached. If anterior segment ischemia occurs, it should be treated with atropine and frequent instillation of topical steroids