OCULAR BLOOD SUPPLY

Sanket Parajuli

Ophthalmic artery: Origin: ICA Enters orbit via Optic canal(Inferolateral) Orbital cavity: lateral to the ON ….medial

to LR, 3rd 6th CN & cil. Ganglion Then turns medially crosses ON lies

inferior to SR Medial wall of orbit: above MR and below

SO Medial end of upper eyelid

Supratrochlear and dorsal nasal arteries

Branches:1. Central artery of the Retina2. Lacrimal artery3. Muscular branches4. Ciliary arteries5. Supraorbital ateries6. Posterior ethmoidal arteries7. Anterior ethmoidal arteries8. Meningeal arteries9. Medial palpebral arteries10.Supratrochlear arteries11.Dorsal nasal arteries12.Recurrent artery

Central artery of the Retina

1st branch of Ophthalmic artery Arises from oph artery as it lies inferolat to ON close

to optic canal Runs forward beneath ON and 1.5cm behind the

eyeball turns upward to pierce dura and arachnoids sheaths of ON

Enters eyeball by piercing lamina cribosa Divides into Superior and inferior branches ( and

temporal and nasal branch of each)

Branches from Central retinal artery Small meningeal branches : supply plial sheath of the ON

Very small anastomoses between plial vessles at distal end of ON and small vessels in the sclera about ON head(short post ciiary art) k/a Circle of zinn

(These anastomoses are too small so for practical purpose central retinal artery = end artery )

Central collateral branches may pass posteriorly within the ON towards optic canal and supply the macular nerve fibers

Lacrimal artery Large branch arises from the ophthalmic artery close to its

emergence from optic canal Runs forward on upper border of LR accompanied by Lacrimal

nerve Passes through lacrimal gland ( supplies it) and then terminal

branches to conjunctiva and eyelids Branches:1. Lateral palpebral arteries passes medially into upper and

lower eyelids and anastomose with medial palpebral arteries2. Zygomatic branches: anastomose with arteries of face and in

temporal fossa3. Muscular branch : lateral rectus

Muscular branches: Variable number of muscular art arise from ophthalmic artery Most branches accompany branches of CN3 Arteries to rectus muscle gives rise to anterior ciliary artery

Ciliary arteries3 groups of Ciliary arteries1. Long posterior2. Short posterior3. Anterior

Long posterior ciliary arteries

Usually 2 in no Arises from ophthalmic art as it crosses the ON Run forward pierce sclera of eyeball medial and lateral to

ON outside the circle formed by the short posterior ciliary arteries

Long posterior ciliary arteries then run forward between sclera and choroid to ciliary body(no branches given)

At the attached margin of iris they divide into upper and lower branches which encircle the iris and anastomose with

…………...anterior ciliary arteries to form major arterial circle of Iris Recurrent branches of long posterior ciliary arteries and

branches from major arterial circle and ant ciliary arteies supply choroid posteriorly as far as equator of eyeball

Short posterior ciliary arteries Arise from ophthalmic artery as it crosses ON divides into 10-20 branches Pierce sclera around entrance of ON and supply choroid

as far forward as the equator of the eyeball Here they anastomose with long posterior ciliary arteries

branches of major circle of the iris and branches of anterior ciliary arteries

numbr of small brnchs of SPCA form an anastomotic ring (ring of zinn) around optic disc

Anterior ciliary arteries Origins from the muscular branches of the

ophthalmic artery to 4 rectus muscles 2 ant ciliary art ass with each rectus muscle

with exception of LR which is provided with 1 ant ciliary art

These arteries supply the sclera and conjunctiva sends branches through sclera at the insertion of recti tendons

These latter twigs join the long post ciliary art to form great arterial circle of the iris

Supra orbital artery Arises from ophthalmic art as it crosses ON Passes superiorly round the medial borders of the

SR and LPS Leaves orbit by passing through supraorbital

notch/foramen and ascends scalp deep to frontalis muscle

Anastomoses with supratrochlear and superficial temp arteries

Supplies LPS, frontal sinus, upper eyelid, forehead and scalp

Posterior Ethmoidal Artery Arises from ophthalmic artery

when the latter reaches medial orbital wall

enter posterior ethmoidal canal

Supplies ethmoidal sinuses, dura of ACF and upper part of nasal mucosa

Anterior Ethmoidal artery

Larger than posterior Ethmoidal artery enters ant ethmoidal canal then enters

ACF through cribiform plate of ethmoid Then descends in a groove on deep

surface of nasal bone to enter face between nasal bone and upper nasal cartilage

Meningeal artery Runs posteriorly through

supra orbital fissure to supply meninges in middle cranial fossa

Medial palpebral arteries

2 medial palp arteries arise from anterior part of ophthalmic artery below the pulley for SO

Descend behind lacrimal sac and pierce orbital septum above and below medial palpebral ligament

Each artery then passes laterally to enter upper and lower eyelid and divides into two branches which form the peripheral and marginal arterial arches

The arch run laterally between orbicularis oculi and tarsal plates

Arches supply eyelids and conjunctiva

Supratrochlear arteries

A terminal branch of ophthalmic artery Leaves orbit by piercing orbital septum above the trochlea Supplies skin of forehead and scalp

Dorsal nasal artery

A terminal branch of ophthalmic artery pierces orbital septum Passes above medial palpebral ligament and then descends to

side of the nose Gives branches to lacrimal sac and anastomose with facial

artery

Infraorbital Artery Arises from maxillary artery in pterygopalatine fossa Enters orbital cavity through inferior orbital fissure Gives off branches to IR and IO and also the lacrimal sac

VEINS OF ORBIT

Tortuous and freely anastomose with one another Have no valves Orbit drained by superior and inferior ophthalmic veins which

in turn drain into cavernous sinus Central retinal vein directly drains into cavernous sinus or into

superior ophthalmic vein

Superior ophthalmic vein medial part of upper eyelid union of a branch of the supraorbital vein

and a branch of facial vein passes posteriorly in orbital fat Communicates with central vein of retina

and near the apex of orbit (it commonly receives inf oph vein)

Also recieves 2 vorticose veins from upper part of eyball

It leaves orbit through upper part of sup orbital fissure to join cavernous sinus

Inferior ophthalmic vein Arises from venous plexus on the

anterior part on the floor of the orbital cavity

It communicates with pterygoid venous plexus through the inferior orbital fissure

Passes posteriorly in orbital fat receives muscular branches and 2

inferior vorticose veins from lower part of eyeball

Drains into cav sinus or empty into pterygoid venous plexus

Central vein of Retina Formed by the union of tributaries that

correspond approximately to the branches of central retinal artery

Leaves eyeball piercing lamina cribosa About 10mm behind eyeball central vein leaves

nerve Vein then drains directly into cavernous sinus or

enters the sup ophthalmic vein

EYELID

Supplied by lateral and medial palpebral arteries

Lateral palpebral arteries – derived from lacrimal art ( br of ophthalmic artery)

Medial palpebral arteries – sup & inf ---derived frm ophthalmic art below trochlea

Each artery divides into 2 branches that pass laterally forming two arches 1. Marginal arterial arch2. Peripheral arterial archThese arches anastomose with lat papebral arteries and with branches of sup temporal transverse facial and infraorbital arteries

Venous drainage Larger and numerous than arteries Pretarsal – drains into angular vein(---IJV) medially

and into superficial temporal vein laterally(---EJV). Posttarsal-drains into orbital veins and deeper

branches of the anterior facial vein and pterygoid plexus

conjunctiva Arises from 2 palpebral arcades in each eyelid and

from anterior ciliary arteries Marginal arcade: perforating br. pierce tarsus Peripheral arcade: perforating br. Pirece palpebral

muscle and gives as and des branchesDes branches: supply tarsal conjunctivaAsc branches: upwards , bend @ fornix & run under bulbar conjunctiva forming posterior conjunctival arteries to supply bulbar conjunctiva..then they proceed towards cornea@ limbus they anastomose with anterior conjunctival arteries( br of ant ciliary arteries)

Venous drainage Numerous than arteries Drain into venous plexus of eyelids and then into superior and

inferior ophthalmic veins

sclera Anterior to insertions of recti muscles the anterior ciliary

arteries form episcleral plexus Posterior part of sclera receives branches from long and short

posterior ciliary arteries

cornea Avascular Capillaries from anterior ciliary arteries of conjunctiva and

sclera end at circumference of cornea

Iris and ciliary body

2 long posterior ciliary arteries and 7 anterior ciliary arteries forms the major arterial circle located in the stroma of the ciliary body

Radial vessels from the major art circle converge in spiral pattern toward pupillary margin ( forms radial ridges seen on ant sur of iris)

On reaching the collarette the arteries anastomose to form incomplete minor arterial circle of iris

choroid

Short ciliary art Recurent branches from Ant ciliar art Run in sinuous manner eventually divide into choriocapillaries(extend

from optic disc to oraserrata)

Segmental arrangement in choroid Posterior ciliary arteries and their branches have a segmental

distribution in choroid Each terminal choroidal arteriole supplies an independent field

or lobule of choriocapillaries Feeding arteiole enters polygonal shaped segment of capillaries

and the draining veins lie at periphery

Venous drainage of uveal tract Anterior ciliary veins drain from ciliary muscle Smaller veins from sclera Venae verticose

Vortex veins

Drains from choroid ciliary body and iris 4 in number ( superior and infeior temporal and

nasal) Located in 1, 5 ,7, 11 o’ clock position Pierce sclera obliquely on each side of SR and IR

(6mm behind the equator) Drain from a) Whole of choroidb) Small veins from ON headc) Tributaries from Iris ciliary process and cil muscle

Superior into sup ophthalmic veins Inferior into inf ophthalmic vein

Retinal blood supply Outer retinal layers(4) are

supplied by diffusion from choriocapillaries

The central retinal artery(inner 6 layers)

Macular region: superior and inferior temporal arteries

Retinal capillaries

Two capillary networks :

Superficial – lies at the level of nerve fiber layer

Deep – lies between inner nuclear and outer plexiform layer - is more dense and complex

Optic Nerve1. Intraoccular part ( optic nerve Head) Surface nerve fiber layer: central

retinal artery Prelaminar layer : SPCA, cilioretinal

art , choroidal arteries Laminar layer : SPCA, branches from

circle of zinn Retrolaminar layer: SPCA ,Plial

plexus Central retinal artery, Recurrent choroidal arteries

Venous drainage : central retinal vein

2) Intraorbital partPlial plexus and br frm ophthalmic art

3) Intracanalicular part: plial plexus branches frm oph art

4) Intracranial partBr frm ICA or Br frm anterior superior hypophyseal artery

Ocular hemodynamics Pressure in Ocular arteries= lower than arteries of the body Pressure in retinal arteries = 25% below ophthalmic artery At MAP = 100mm Hg @ brachial artery Mean ophthalmic artery pressure = 77mm Hg(Retinal artery = 70 mm Hg)

Pressure in intraocular veins where they enter sclera = IOP (10-15mm Hg) under normal conditions

When IOP > 10-15mm Hg Uveal venous pressure directly proportional to IOP(Partial collapse of intrascleral veins)

Local rise in external venous pressure doesnt change Uveal VP much unless there is a change in IOP

Large rise in pressure in extraocular VP raises pressure in choroid and produces intraocular venous congestion

Ocular blood flow: Laminar : Retinal arterioles and venules

Iris Flow in choroid difficult to describe due to

architecture of choriocapillaries ( although considered laminar)

Retinal blood flow in a healthy adult = 170ml/100gm/min

Of total ocular blood flow65-85% choroid10-35% iris and ciliary body5% retinal vessles

Choroid a heat sink—imp use of photocoagulation or coherent light in treatment of diseases of retina

O2 extraction from retinal vessels high

O2 extraction from choroidal vessels is less

IOP and ocular blood flow As IOP is raises Blood flow ceases in following order (Experimental studies)a) Anterior uveab) Choroidc) Retina

Studies have shown:As IOP increases 1. Choroidal BF decreases ( A-V O2 difference increases) 2. Further choriocapillaries fill in patchy manner

Control of ocular blood flow

1) perfusion pressure= MAP-IOPRise in IOP or fall in MAP = lower perfusion pressure thus the blood flowDiagram( with increase in IOP no decrease in retinal blood flow upto a certain level) due to autoregulation

No auto regulation in choroid thus perfusion pressure affects blood flow through choroidal vessels

2)Autoregulation (Retina ,ciliary body, iris)

Property which permits constant blood flow over a range of perfusion pressure

Myogenic TheoryPerfusion pressure when changed …..pacemaker cells in arterioles detects…..smooth cells contraction causing vasoconstriction or dilation

Metabolic TheoryArteriole adjust blood flow by producing certain metabolites

Nervous control of ocular blood flow Retinal vessels are not under

nervous control Choroidal vessels innervated by

both sympathetic and parasympathetic vessels

Sympathetic : ciliary arteries and also the extraocular part of central retinal arteryRich sympathetic fibers in iris, ciliary process and choroid NO sympathetic nerves in Retina

Parasympathetic: less cear exists in ciliary processes and choroid Terminal bundles of PSN present in choroid expect in

choriocapillaries Perhaps they cause increase in blood flow by causing

vasdilation

Chemical control

Hypercarbia= vasodilation of uveal tissue= rise in IOP 100% O2 = slight vasoconstriction of retinal vessels---not much

fall in O2 tension to affect retinaHowever in premature infants –marked vasoconstriction—inhibition of vascular development and later obliteration of vessles—ROP(frequent ophthalmoscopic examination is required for premature infants under O2 ) 7% CO2 and 21%O2 = moderate dilation of visible retinal vesselsRetinal blood flow increased by 300-400% Thus given in emergency management of CRAO

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