Lecture 6 - Blood Supply

Ocular Anatomy

What is systemic circulation?

• Carries oxygenated blood from the heart to the body’s tissues

• Returns deoxygenated blood to the heart

What is pulmonary circulation?

• Carries deoxygenated blood from the heart to the lungs for oxygenation

• Returns oxygenated blood to the heart

What is the aorta?

The largest artery in the human body; carries oxygenated blood from the heart’s LV to the rest of the body

What are the branches of the aorta?

• Ascending aorta

• Aortic arch

• Descending aorta

What is the ascending aorta?

• Arises from the left ventricle of the heart

• Contains the aortic valve (helps prevent backflow)

• Gives rise to the coronary arteries that supply the heart

What are the branches of the aortic arch?

• Brachiocephalic artery

• Left common carotid artery

• Left subclavian artery

What are the branches of the brachiocephalic artery? (aortic arch branch)

• Right subclavian artery

• Right common carotid artery

What are the branches of the descending aorta?

• Thoracic aorta

• Abdominal aorta

Where is the thoracic aorta located and what does it supply? (branch of descending aorta)

Above the diaphragm, supplies chest organs

Where is the abdominal aorta located and what does it supply? (branch of descending aorta)

Below the diaphragm, supplies the abdominal organs and legs

• Splits into R and L common iliac arteries

What structure separates the thoracic and abdominal aorta?

The diaphragm

Where do the vertebral arteries come from?

Arise from the subclavian arteries (from the brachiocephalic artery)

What do the vertebral arteries supply?

Supply blood to posterior parts of the brain

What do the right and left vertebral arteries form?

They form the basilar artery, which splits into the posterior cerebral arteries (PCAs)

• This is the vertebrobasilar system

What vessels connect the posterior cerebral arteries (PCAs) to the internal carotid arteries (ICAs)?

The posterior communicating arteries

What is the Circle of Willis?

A network of arteries that connect blood supply from the anterior and posterior parts of the brain

What 2 major arteries anastamose to form the Circle of Willis?

Internal carotid arteries (anterior) and posterior cerebral arteries (posterior)

• Connected by posterior communicating arteries

What is the purpose of anastamoses within the circle of willis?

Provide alternative routes for blood flow in case of blockages and help maintain a constant blood supply to the brain

What are the common carotid arteries and what do they supply?

Major arteries that supply oxygenated blood to the head and neck, particularly the brain, face, scalp, and neck structures

• Splits into R and L common carotid

What does the right common carotid artery arise from?

From the brachiocephalic artery

What does the left common carotid arise from?

Directly from the aortic arch

What are the branches of the carotid arteries?

Both R and L common carotid arteries split into the internal carotid artery (ICA) and the external carotid artery (ECA)

What does the internal carotid artery (ICA) supply?

Structures in the anterior cranium, including the brain and eyes

What does the external carotid artery (ECA) supply?

Superficial areas of the head and neck, supplies a small portion to the ocular adnexa

What is the pathway of the internal carotid artery?

• Runs up through the neck

• Enters skull through the carotid canal

• Exits canal and enters cavernous sinus

• Emerges from the canal and branches off

What nerves surround the ICA throughout its pathway?

A sympathetic nerve plexus originating from the superior cervical ganglion

What is the first major branch from the ICA after it emerges from the cavernous sinus?

Ophthalmic artery

What does the ophthalmic artery supply? (branch of ICA)

Upper 2/3 of orbital contents; main supply to the eye, orbit, and some adnexal structures

What is the pathway of the ophthalmic artery?

Arises from the ICA, passes through the optic canal within the CTR (inferolateral to optic nerve), runs towards the medial orbit and branches off

What are the branches of the opthalmic artery from posterior to anterior?

• Central retinal artery

• Lacrimal artery

• Posterior ciliary arteries (2-3)

• Ethmoid arteries (2)

• Supraorbital artery

• Muscular arteries (2)

• Medial palpebral arteries (sup/inf)

• Dorsonasal artery

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What is the pathway of the central retinal artery (CRA)?

• Arises from the ophthalmic artery

• Crosses under the optic nerve

• Enters the meningeal sheath of the optic nerve

• Travels through the middle of the nerve

• Passes through the lamina cribrosa and enters optic disc nasal to the center

• Surrounded by sympathetic nerve plexus

What does the central retinal artery (CRA) supply?

Supplies the prelaminar portion of the optic nerve (optic nerve and pia mater) and the inner 2/3 of the retinal layers (inner retina)

• Does NOT supply the fovea

What is the lamina cribrosa?

An opening in the posterior sclera that allows the optic nerve to pass through

Describe the role of the central retinal artery in the blood-retina barrier.

The CRA branches are non-fenestrated capillaries with tight junctions. These form a protective mechanism that allows for select entry into retinal tissue.

What is the lacrimal artery?

One of the largest branches of the ophthalmic artery, serves structures near the lateral orbit

What is the pathway of the lacrimal artery?

• Branch of ophthalmic artery

• Runs along superolateral orbit parallel to lacrimal nerve

• Terminal branches pass through the lacrimal gland and pierce orbital septum

• Enter lateral side of upper/lower lids

• Other terminal branches enter conjuctiva to form capillary network

What specific structures does the lacrimal artery supply?

• Lacrimal gland

• Lateral portions of upper/lower lids

• Lateral conjunctiva

• Lateral rectus muscle

(Lateral structures of the orbit)

What are the branches of the lacrimal artery?

• Recurrent meningeal artery → passes through superior orbital fissure

• Zygomaticotemporal artery

• Zygomaticofacial artery

How do the palpebral arcades arise from the lacrimal artery?

Lacrimal artery → lateral palpebral arteries → combine with medial palpebral arteries → palpebral arcades

What are the ciliary arteries?

Branches of the ophthalmic artery that divide into short posterior ciliary arteries (SPCA) and long posterior ciliary arteries (LPCA)

• Give off branches to supply the retrobulbar (behind the globe) optic nerve

• Supply the optic nerve, choroid, and ciliary bodies

What are the short posterior ciliary arteries (SPCA)?

Ciliary arteries that enter the sclera in a ring around the optic nerve and form an arterial network within the choroidal stroma

• Form the choriocapillaris which is part of the stroma and sustains photoreceptors

What do the short posterior ciliary arteries supply?

• Outer retina

• Fovea

• Prelaminar and laminar optic nerve

• Choroid (layer between retina and sclera)

What are the choriocapillaris?

• Part of the SPCA

• Dense network of fenestrated capillaries beneath Bruch’s membrane

• Supply the outer retina and fovea

• Form the cilioretinal artery in 15-50% of people (supply additional blood to macula)

What is the Circle of Zinn (Zinn-Haller)?

A group of vessels that encircle the optic nerve at the choroid level and supply the laminar optic nerve

• Formed by branches of the SPCA

What are the long posterior ciliary arteries (LPCA) and what do they supply?

Ciliary arteries that contain 2 branches and supply the iris and ciliary body

Also anastomose with SPCAs to supply the choroid

How do LPCAs form the major arterial circle?

They branch superiorly and inferiorly in the ciliary body, anastomosing with the anterior ciliary arteries to form the major arterial circle of the iris

What is the major arterial circle of the iris?

A circular-shaped artery that supplies the ciliary body and the iris

• Made from LPCAs

• Located in the ciliary body (not actually part of the iris!)

What are the ethmoid arteries?

Branches of the ophthalmic artery (2) that split into the posterior ethmoid artery (towards the nasal side) and the anterior ethmoid artery

What does the posterior ethmoid artery supply?

• Posterior ethmoid sinus

• Sphenoid sinus

• Nasal cavity

What does the anterior ethmoid artery supply?

• Anterior and middle ethmoid sinuses

• Sphenoid sinus

• Frontal sinus

• Nasal cavity

• Skin of nose

(all sinuses except maxillary!)

What is the supraorbital artery?

A branch of the ophthalmic artery that passes through the supraorbital notch and divides into two branches

What does the supraorbital artery supply?

• Skin and muscles of the forehead

• Anterior scalp

• Upper eyelid

• Superior rectus, superior oblique, and levator muscles

• Periorbita

What are the muscular arteries?

2 branches (lateral and medial) of the ophthalmic artery that supply the extraocular muscles

What does the lateral branch of the muscular artery supply?

Lateral rectus, superior rectus, superior oblique, and levator muscles

What does the medial branch of the muscular arteries supply?

Medial rectus, inferior rectus, and inferior oblique muscles

What is the blood supply of the medial rectus?

Medial muscular artery

What is the blood supply of the lateral rectus?

Lateral muscular artery and lacrimal artery

What is the blood supply to the superior rectus?

Lateral muscular artery, lacrimal artery, and supraorbital artery

What is the blood supply to the inferior rectus?

Medial muscular artery and infraorbital artery*

What is the blood supply to the superior oblique?

Lateral muscular artery, supraorbital artery

What is the blood supply to the inferior oblique?

Medial muscular artery and infraorbital artery

What are the anterior ciliary arteries?

7 branches from the muscular artery, usually 2 in each rectus muscle

• Lateral rectus has 1 only

They run forward along the rectus muscles and pierce the sclera near the limbus

What do the anterior ciliary arteries supply?

• Conjunctiva

• Episclera

• Ciliary body

• Iris

What do the anterior ciliary arteries anastomose to form?

• Anastomose with LPCA to form the major circle of the iris

• Form the minor circle of the iris at the pupil margin

What are the medial palpebral arteries?

2 branches of the ophthalmic artery that split into the superior and inferior medial palpebral arteries

What do the medial palpebral arteries supply? (superior and inferior)

• Medial upper and lower lids

• Lacrimal canaliculi

• Anastomose with branches of lacrimal artery to form palpebral arcades → supply eyelid structures

What are the terminal branches of the ophthalmic artery?

Supratrochlear artery and dorsonasal artery

What is the supratrochlear artery and what does it supply?

A terminal branch of the ophthalmic artery that supplies:

• Skin of forehead and scalp

• Muscles of forehead

• Medial upper eyelid

What is the dorsonasal artery and what does it supply?

Terminal branch of the ophthalmic artery that supplies:

• Medial canthus

• Medial eyelids

• Nasolacrimal duct

• Lacrimal sac and caruncle

• Root of nose

What is the facial artery?

A branch of the external carotid artery that supplies superficial areas of the face

• Arises near the angle of the mandible

• Gives rise to the angular artery

What structures does the angular artery (branch of facial artery) supply?

• Lacrimal sac

• Medial lower lid

• Skin of cheek

(medial portions of the orbit)

What is the superficial temporal artery?

A terminal branch of the external carotid artery supplies areas near the orbit

• Splits into the anterior temporal artery, zygomatic artery, and transverse facial artery

What does the anterior temporal artery supply?

Skin and muscles of forehead (superior portions of the face)

What does the zygomatic artery supply?

Lateral aspect of orbicularis muscle

What does the transverse facial artery supply?

Skin of cheek

What is the maxillary artery and what does it supply?

Branch of the ECA that supplies the lower 1/3 of the orbit

• Infratemporal fossa

• Pterygopalatine fossa

What is the infraorbital artery?

Branch of the maxillary artery (which is a branch of the ECA)

What is the pathway of the infraorbital artery?

• Enters orbit through inferior orbital fissure

• Runs along infraorbital groove in the maxillary bone

• Passes through the infraorbital canal

• Exits through the infraorbital foramen

What does the infraorbital artery supply?

• Lower eyelid

• Lacrimal sac

• Inferior rectus

• Inferior oblique

• Maxillary sinus

• Teeth of upper jaw

(inferior aspects of the orbit)

What does the infraorbital artery anastomose with?

Angular and dorsonasal arteries

What forms the superior ophthalmic vein?

Formed by joining of angular and supraorbital veins within the orbit

What is the pathway of the superior ophthalmic vein?

Enters orbit through supraorbital notch (as the supraorbital vein) → exits orbit through superior orbital fissure above the CTR → drains into the cavernous sinus

What veins drain into the superior ophthalmic vein?

• Anterior and posterior ethmoid veins

• Muscular veins

• Lacrimal veins

• Central retinal vein

• Superior vortex veins

What is the central retinal vein?

• Drains the venous branches of the retina

• Exits optic nerve behind the lamina cribrosa alongside CRA

• Either joins superior ophthalmic vein or drains directly into cavernous sinus

What are the vortex veins?

Veins that drain the choroid; 4-5 veins; located in each quadrant of the globe

• Exit posterior to the equator

• Can be seen with an indirect ophthalmoscope and dilated pupil (look like spiderweb clusters on the retina)

What is the drainage pathway of the superior vortex veins?

Drain into superior ophthalmic vein → cavernous sinus

What is the drainage pathway of the inferior vortex veins?

Drain into the inferior ophthalmic veins → pterygoid venous plexus OR cavernous sinus

What does the inferior ophthalmic vein drain?

• Lower and lateral muscles

• Inferior conjunctiva

• Lacrimal sac

• Inferior vortex veins

Then drains into cavernous sinus OR pterygoid venous plexus

What are the anterior ciliary veins?

Drain the conjunctiva, episclera, and anterior portion of ciliary muscles

Then drain into muscular veins of rectus muscles → superior and inferior ophthalmic veins

What is the pathway of the infraorbital vein?

Formed by several veins of the face → enters infraorbital foramen → passes posteriorly through infraorbital canal and groove → receives branches from inferior orbit → communicates with inferior ophthalmic vein → drains into pterygoid venous plexus

What is the cavernous sinus?

A large venous channel formed by splitting the dura mater on either side of the body of the sphenoid bone.

• Extends from behind the superior orbital fissure to the petrous portion of the temporal bone

What runs through the medial part of the cavernous sinus?

• Internal carotid artery

• CN VI (abducens)

What runs through the lateral part of the cavernous sinus?

• CN III (oculomotor)

• CN IV (trochlear)

• CN V-1 (ophthalmic)

• CN V-2 (maxillary)

What does the cavernous sinus drain into?

Drains into the superior and inferior petrosal sinuses → both drain into the internal jugular vein

What structures empty into the submandibular lymph nodes?

Medial eyelids, medial canthal structures, lacrimal sac

What structures empty into the parotid and preauricular lymph nodes?

Lateral eyelids and lacrimal gland

What are the effects of aging on ocular circulation?

• Decreases in density of choroidal and retinal capillary beds, decreases in choroidal and retinal vessel diameter (higher blood pressure)

• Epithelial dysfunction resulting in increased vascular tone, reduction in vessel distensibility (become stiffer), and decrease in tissue perfusion