OCULAR BLOOD SUPPLY AND DRAINAGE
I.
Distributing Blood to Tissues:
A. General Vascular Organization
1. Arteries – blood away from heart
2. Capillaries – exchange between tissues and blood occurs here. Supplied by
arterioles and drained by venules
3. Veins – Blood back to heart
B. Arteries control blood flow through capillary beds, and veins regulate blood volume.
1. Arteries and Veins have 3 layers:
 Tunica Intima
 Tunica Media
 Tunica Adventitia
C. Capillary beds in a tissue may be independent or interconnected.
1. Segmented = one inflow has one outflow; this is true in the retina which has a
segmented, end-arterial system  no redundancy.
2. Overlapping = many inflows have many outflows; this is true in choriocapillaris
 redundant anasthamoses.
D. The interchange between blood and cells depends partly on structure of vascular
endothelium.
1.
2.
3.
Fenestrated Endothelium = endothelium has holes that make capillary highly
permeable.
 Found in choriocapillaris
 Found in ciliary process
Continuous Endothelium = endothelium is unbroken b/c space between 2 cells has
tight junction; this is in most capillaries.
 Found in iris
 Make up blood-retina barrier
Dis-continuous Endothelium = endothelium has pores permitting unregulated
blood flow in and out of capillaries.
E. Capillary endothelium is renewable; and capillary beds can change. Capillary beds
grow by a process involving cell division, migration, and vacuole formation that
creates a sprout from an existing capillary wall.
F.
Neovascularization is a response to altered functional demands.
 Neovascularization = formation of new capillary beds from existing blood
vessels. Is stimulated by change in nearby tissue (ie wound or need for O2).
G. Structurally weakened capillaries may be prone to excessive neovascularization. This
can occur in the retina due to diabetes or vessel occlusion.
VS 112 Ocular Anatomy
UAB School of Optometry
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II.
General Ocular Blood Flow
A.
Ocular Blood Flow
a. Vasculature of eye
i. Retina – retinal vessels supply blood to two-thirds of the retina
ii. Uvea-iris, ciliary body, choroids – supplies remaining third
b. Vasculature of Surrounding Structures
i. EOM
ii. Skin/eyelids
iii. Sinuses
c. Direction of Flow
i. Internal Carotid Artery branches into the
ii. Opthalmic artery which then branches into:
1. central retinal artery which then branches to the four
quadrants of the retina
2. posterior ciliary artery which branches into two long
posterior ciliary arteries (to ciliary body and anterior
choroids) and 10-20 short posterior ciliary arteries to
the choroids/choriocapillaris
3. muscular arteries which branches into the anterior
ciliary arteries to the muscles and iris.
III.
The Ophthalmic Artery
A. Ophthalmic Artery distributes blood to the eye and its surroundings.
1.
Ophthalmic Artery = a branch from the internal carotid that passes through
the optic foramen. This branches posteriorally into 3 branches:
 Central Retinal Artery – goes to the retina
 Posterior Ciliary Arteries – 2 branches
 Muscular Arteries – 5 to EOM
2.
Central Retinal Artery = pierces the meninges of the optic nerve.
 Supplies pia mater & center of optic nerve.
 Also supplies inner 2/3 of retina.
 Capillaries terminate in inner & outer edges of Inner Nuclear Layer
and the inner & outer edges of Ganglion Cell Layer.
 Superior & Inferior Temporal Artery & Vein = branches off central
retinal artery.
 Is “Segmented, End-Arterial System” = no shunts in branching; no
overlap in regions supplied by terminal arterioles. Therefore, is
vulnerable to Arterial & Venous Branch Occlusion.
 There is NO redundancy  an occlusion/infarction will kill
the nerve cells around  become translucent “Cotton Wool
Spot” – blind at this spot b/c Ganglion Cells are dead.
 There are major branches of Central Retinal Artery to 4 quadrants.
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UAB School of Optometry
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3.
Posterior Ciliary Arteries = 2 branches, lateral & medial that supply blood to
uveal tract.
 Long Posterior Ciliary Artery = pierces sclera nasally &
temporally to optic nerve. Contributes to retinal circulation. Runs
forward in choroids  ciliary body with VERY FEW branches.
Does NOT contribute extensively to choroidal circulation.
 There are 2 – medial & lateral.
 Can help orient the horizontal plane of eyeball.
 Short Posterior Ciliary Artery = form choroidal circulation which
supplies outer 1/3 of the retina. Enters close to eye as “circle of
zinn” around optic nerve head. Terminates in the choriocapillaris.
 May give rise to a Cilioretinal Artery – supplies the inner
retina between nerve head & fovea (insurance against
blockage of Central Retinal Artery).
 There are about 10-20 – form “Circle of Zinn” = is
continuous, protect from occlusions.
 Also supplies the nerve head and optic nerve just behind
the eye.
4.
Muscular Arteries = 5 branches to supply EOMs. (4 run off ophthalmic
artery and 1 off lacrimal artery).
 Medal Rectus – most posterior artery off ophthalmic artery.
 Superior Oblique
 Inferior Oblique & Inferior Rectus
 Superior Rectus & Levator Muscle – most anterior artery off
ophthalmic artery.
 Lateral Rectus = only muscular artery off Lacrimal Artery.
 Muscular Arteries – can also become the Anterior Ciliary Arteries
to muscles & iris.
B. Branching of the Choroid Vessels:
1. Each of the Short Posterior Ciliary Arteries supplies a different part of the
choroids. These arteries branch in the choroid.
2. Haller’s Layer = large vessels found near sclera of choroid.
3. Sattler’s Layer = medium vessels found near retina of choroid.
4. Choriocapillaris = smallest branches of choroid that supply the
photoreceptors. They are a dense meshwork of capillaries that are extremely
anastomotic. There is a functional segmentation of choriocapillaris b/c
blood must flow from high  low pressure (from arteries  veins).
 Peripheral Retina – are more Venules >>> than Arteries. Are unable
to compensate for arterial blockage.
 Central Retina – are more Arteries >>> than Venules. Are unable to
compensate for venous blockage.
 Fenestrated Capillaries in choriocapillaris – more permeable for
diffusion.
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UAB School of Optometry
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C. Anterior Ciliary Arteries = branches off the Muscular Arteries (which are
branches off Ophthalmic Artery).
1. These arteries have capillaries to supply the EOM (rectus muscles).
2. There are 7 arteries which supply the 4 Rectus Muscles.
 Lateral Rectus – supplied by 1 anterior ciliary artery.
 Superior, Inferior, & Medial Rectus – all supplied by 2 anterior ciliary
arteries.
3.
These arteries emerge off the Muscular Arteries several mm posterior to
muscle tendons. These arteries are running on top of the muscle, and then
DIVE into the conjunctiva (are not superficial).
4.
They then Bifurcate after passing over the tendons becoming the Episcleral
Arteries & Major Perforating Arteries.
 Episcleral Arteries = superior branch of Anterior Ciliary Arteries.
Will run anteriorally toward cornea to form the Corneal Arcades, and
posteriorally to conjunctiva to the Superficial Marginal Plexus.
 There are 7 Episcleral Arteries (1 per Ant. Ciliar Artery).
 All 7 of these arteries will form “Episcleral Circle” – which
runs in a circle around the eye (can see superficially), in the
limbus.
 Superior Marginal Plexus = conjunctival arteries (branch off
Episcleral Artery).
 Corneal Arcades = arteries that supply the periphery of the
cornea (branch off Episcleral Artery). They DO NOT invade
the cornea b/c clear!

Major Perforating Arteries = inferior branch of Anterior Ciliary
Arteries. These will branch to form the Intramusclar Circle in ciliary
muscle, and the Minor Arterial Circle of the iris.
 Intramuscular Circle – in ciliary muscle = supplies the ciliary
body (except ciliary process). Branches of this circle will help
form Minor Arterial Circle of the iris.
D. Long Posterior Cililary Arteries:
1.
2.
3.
4.
Dive into the sclera ~ 4mm away from optic nerve & run unbranching to
anterior portion of the eye (for anterior retina, ciliary body, and iris).
These travel forward in the choroid to ciliary body.
Branches form Major Arterial Circle – supplies the ciliary processes with
capillaries and Minor Arterial Circle of iris.
Minor Arterial Circle (of the Iris) = is about at the collarette. This circle is
formed form branches off Major Arterial Circle (from Long Post.Ciliary
Arteries) and Intramuscular Circle (from Major Perforating Arteries off
Anterior Ciliary Arteries). Branches off this circle travel forward to supply
the Sphincter Muscle of the Iris.
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UAB School of Optometry
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


Major Arterial Circle may be incomplete (would be at Superior &
Inferior Poles)  These portions would then only be supplied by
the Minor Arterial Circle.
Medial & Lateral Poles – have dual blood supply from both Major
and Minor Arterial Circle.
Iris – has Continuous Capillaries (lots of tight junctions) to prevent
any leaking! These capillaries must be flexible.
E. Lacrimal Artery = on of largest branches off Ophthalmic Artery.
1. Supplies the Lacrimal Gland, Lateral Rectus Muscle, and skin and muscles
of upper brow.
2. Gives rise to Lateral Palpebral Artery (which supplies the eyelids).
3. Run through orbit (at Lacrimal Fossa)  Lacrimal Gland.
F.
Anterior and Posterior Ethmoid Arteries:
1. Arise from Ophthalmic Artery.
2. Leave orbit through Anterior & Posterior Ethmoid Foramen (in Ethmoid
Bone).
3. These arteries supply the vasculature for mucosa of the sinuses and for skin
of the nose.
G. Supraorbital Artery = one of terminal branches of Ophthalmic Artery.
1. Runs above the eye & passes thru Supraorbital Notch (or Foramen).
2. Supplies the skin and muscles of the upper eyelid, brow & forehead.
H. Supratrochlear Artery = one of terminal branches of Ophthalmic Artery.
1. Runs above the trochlea as it exits the orbit.
2. Supplies skin and muscle in the medial part of the eyebrow & forehead.
IV.
I.
Dorsal Nasal Artery = one of terminal branches of Ophthalmic Artery.
1. Runs below the trochlea to exit orbit.
2. Supplies the eyelid, Lacrimal Sac (including Horner’s Muscle), and the skin
and muscle along the nose.
3. Anasthamoses with Angular Artery.
J.
Medial Palpebral Artery = may be a branch off Ophthalmic Artery or Dorsal
Nasal Artery.
1. Supplies blood to the eyelids.
2. At the eyelids – all arteries split up & anasthamose with one another to form
the Palpebral Arcades. This will include Medial Palpebral Artery & Lateral
Palpebral Artery and Lacrimal Artery.
 Eyelids are also supplied by External Carotid Artery (Facial &
Maxillary Artery) branches = Facial Artery & Infraorbital Artery.
Facial & Maxillary Arteries (off External Carotid Artery)
A. Facial Artery:
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UAB School of Optometry
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1.
Angular Artery = branch off Facial Artery that helps supply the Palpebral
Arcades.
B. Maxillary Artery:
1. Infraorbital Artery = branch off the Maxillary Artery that helps supply the
Palpebral Arcades.
 Enters the orbit via Inferior Orbital Fissure.
 Exits the orbit via Infraorbital Canal – will go and supply blood to
cheeks.
V.
Drainage of the Ophthalmic Vein to Cavernous Sinus.
A. Superior ophthalmic vein- drains blood from upper part of orbit. Leaves the orbit
via the Superior Orbital Fissure. Collects drainage from:
1. Central Retinal Vein = drainage from retina.
2. Anterior & Posterior Ethmoid Vein = drainage of ethmoid sinus.
3. Superior Vortex Vein = drains superior choroid & ciliary body.
4. Drains the Muscular Arteries from Superior Oblique, Medial Rectus,
Superior Rectus, and Levator Muscle.
5. Receives part of drainage from Facial Vein, which receives drainage from:
 Angluar Vein
 Supraorbital Vein
 Supratrochlear Vein
B. Inferior ophthalmic vein- drains blood from lower structures of orbit. Leaves the
orbit via the Superior Orbital Fissure. Collects drainage from:
1. Lacrimal Vein = vein draining the lacrimal gland.
2. Inferior Vortex Vein = drains inferior choroid & ciliary body.
3. Drains the Muscular Arteries from Lateral Rectus, Inferior Rectus, and
Inferior Oblique.
4. Receives part of drainage from Facial Vein, which receives drainage from:
 Angluar Vein
 Supraorbital Vein
 Supratrochlear Vein
C. Cavernous Sinus = main pathway of venous drainage out of the eye that wraps
around the pituitary gland and is very large (= sinus) behind Optic Chiasm. This
will drain into the Internal Jugular Vein.
VI.
Anterior segment drainage:
A. Recurrent Conjunctival Veins & Corneal Arcades drain into  Superificial
Marginal Plexus which drains into Conjunctival Veins which drain into the
Episcleral Vein.
B. Aqueous Fluid drains into the Canal of Schlemm which drains into  Aqueous
Vein of Asher which drain into Episcleral Vein.
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UAB School of Optometry
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C. Blood also moves from Canal of Schlemm which drains into Deep Scleral Plexus
into the Ciliary Plexus which drains into Episcleral Vein.
D. Blood from Intrascleral Plexus drains with blood from Deep Scleral Plexus into
the Ciliary Plexus  drains into Episcleral Vein.
E. Episcleral Vein drains into  Anterior Ciliary Vein which drains into 
Superior Ophthalmic Vein.
F.
IMPORTANT: There are NO venous equivalents to the Intramuscular Artery
(from muscles of ciliary body) and Major Arterial Circles of the ciliary body.
Instead, blood from ciliary body drains into Vortex Veins & Episcleral Veins.
G. Drainage of the iris and ciliary body:
1. Small veins run radially toward the root of the iris.
2. These vessels continue through the ciliary body, merge with veins of the
choroid and drain into the vortex veins (via choriocapillaris).
3. The ciliary muscle is drained by the vortex vein and anterior ciliary vein.
H. Central Retinal Vein = drain inner 2/3 of the retina.
1. The capillary beds within the retina are drained by venules that subsequently
drain into branches of the central retinal vein.
2. All blood vessesl join at the Optic Nerve and leave through the Central
Retinal Vein. Central Retinal Vein also drains blood of the optic nerve.
3. There is no overlap in the regions drained by the venules  vulnerable to
venous branch occlusions.
4. It is vulnerable to high pressure in the arteries, abnormally high IOP, and
abnormally high CSF.
I.
Vortex Veins = four vortex veins that drain the uveal tract (choroid, iris & ciliary
body).
1. The 4 vortex veins are the Superior, Inferior, Lateral & Medial. These are
easy to find on the back of the eye.
2. Drain into the superior and inferior ophthalmic veins.
3. Zones of overlap have shunts and are protected from blockage.
J.
Muscular veins = drain the extraocular muscles parallel to the arteries.
1. Drain blood from muscle’s capillary beds and anterior ciliary veins into the
Ophthalmic Veins OR Vortex Veins.
K. Lacrimal veins:
1. Drain the lacrimal gland into the Superior Ophthalmic Vein or Superior
Vortex Veins.
L. Infraorbital vein:
1. Drains blood from the eyelids into the Venous Pterygoid Plexus (which is
outside the orbit).
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UAB School of Optometry
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M. Supraorbital Vein and Supratrochlear Vein:
1. Drain the skin and muscles of the forehead, brow, and upper eyelid.
N. Angular and Facial Veins:
1. Angular Vein = continues down alongside the nose to become the Large
Facial Vein.
2. Facial Veins forms anathamoses with the Inferior Ophthalmic and
Infraorbital Veins and drains into the Internal Jugular Vein (outside of the
orbit).
3. Drains the lower eyelids and skin and muscles around the orbit.
4. Advantage of the Angular/Facial System: Provides alternative drainage
routes other than Internal Jugular.
5. Disadvantage of the Angular/Facial System: There is a risk that infection
can spread from face  Cavernous Sinus (Thrombosis).
O. Anterior and Posterior Ethmoid Veins:
1. Drain the ethmoid sinuses into the superior ophthalmic vein.
2. Anterior & Posterior Ethmoid Foramen = contain nerve, artery, and vein all
running through one hole.
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UAB School of Optometry
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