Lecture 2 - Orbital and Ocular Blood Supply
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Ocular Physiology
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What is the function of systemic circulation?
It carries oxygenated blood from the heart to tissues via arteries and returns deoxygenated blood to the heart via veins.
What is the function of pulmonary circulation?
It carries deoxygenated blood from the heart to the lungs for oxygenation and returns oxygenated blood to the heart.
Which artery supplies the head and neck?
The common carotid artery.
What are the two divisions of the common carotid artery?
The internal carotid artery and the external carotid artery.
What does the internal carotid artery supply?
Anterior cranial structures, including the eyes.
What does the external carotid artery supply?
Superficial areas of the head and neck, with a small portion supplying the ocular adnexa.
How does the internal carotid artery enter the skull?
Through the carotid canal in the temporal bone.
Which cranial nerve ganglion is the ICA near as it enters the skull?
The trigeminal (CN V) ganglion.
Where does the ICA pass after entering the skull?
Through the cavernous sinus along the medial wall.
Which cranial nerves run near the ICA in the cavernous sinus?
Abducens nerve (CN VI) and oculomotor nerve (CN III).
What neural structure surrounds the ICA in the cavernous sinus?
A sympathetic nerve plexus from the superior cervical ganglion.
What causes ocular ischemic syndrome?
Severe atherosclerosis or occlusion of the carotid arteries leading to hypoperfusion of the eye and orbit.
What ocular changes result from ischemia in ocular ischemic syndrome?
Ischemia leads to neovascularization.
What are symptoms of ocular ischemic syndrome?
Painful vision loss.
What diagnostic test is indicated for ocular ischemic syndrome?
Carotid Doppler/ultrasound.
What is the first branch of the internal carotid artery?
The ophthalmic artery.
What does the ophthalmic artery supply?
The main blood supply to the globe and adnexa.
Through which structure does the ophthalmic artery enter the orbit?
The optic canal in the lesser wing of the sphenoid bone.
How does the ophthalmic artery enter the orbit relative to the optic nerve?
Within the dural sheath of the optic nerve.
What is the initial course of the ophthalmic artery in the orbit?
It runs along the optic nerve for a short distance, then crosses toward the medial wall.
How many main branches does the ophthalmic artery divide into?
9 branches
What are the branches of the opthalmic artery?
Central retinal artery
Lacrimal artery
Posterior ciliary arteries (2-3)
Ethmoid arteries (2)
Supraoprbital artery
Muscular arteries (2)
Medial palpebral arteries (superior and inferior)
Supratrochlear artery
Dorsonasal artery
(Careful Little People Enjoy Seeing Many Many Small Details)
What are the terminal branches of the opthalmic artery?
Supratrochlear artery and dorsonasal artery.
What is the first branch of the ophthalmic artery?
The central retinal artery.
What does the central retinal artery supply?
The inner retinal layers.
How does the CRA enter the optic nerve?
It enters the meningeal sheath at the intraorbital segment of the optic nerve.
What do collateral branches of the CRA supply?
The optic nerve and pia mater.
Where does the CRA enter the eye?
Through the lamina cribrosa into the optic disc.
How does the CRA branch within the retina?
It branches superiorly and inferiorly, then nasally and temporally.
What happens when the central retinal artery is occluded?
Retinal nonperfusion occurs.
What artery may provide backup blood supply to the macula in CRAO?
The cilioretinal artery.
Is the lacrimal artery a large or small branch of the ophthalmic artery?
One of the largest branches.
What structures does the lacrimal artery supply?
The lateral rectus muscle and the lacrimal gland.
When does the lacrimal artery leave the ophthalmic artery?
Right after the ophthalmic artery enters the orbit.
What path does the lacrimal artery take in the orbit?
It runs along the lacrimal nerve and lateral rectus.
What branches arise from the lacrimal artery?
Recurrent meningeal artery
Zygomaticofacial artery
Zygomaticotemporal artery
Lateral palpebral arteries (superior and inferior)
What does the superior lateral palpebral artery supply?
The lateral upper eyelid.
What does the inferior lateral palpebral artery supply?
The lateral lower eyelid.
What do lateral palpebral arteries anastomose with?
Medial palpebral arteries to form palpebral arcades.
How many posterior ciliary arteries are there?
2, one on each side of the globe (lateral and medial divisions).
What do the posterior ciliary arteries branch into before entering the globe?
Short posterior ciliary arteries (SPCAs)
Long posterior ciliary arteries (LPCAs)
Where do the branches of the PCA enter?
The SPCA and LPCA enter the posterior aspect of the orbit.
How do SPCAs arise?
They branch from posterior ciliary arteries before entering the globe.
How many branches do SPCAs form?
Approximately 10–20 branches.
Where do SPCAs enter the eye?
Through the sclera in a ring around the optic nerve.
What structure do SPCAs form around the optic nerve?
The circle of Zinn.
What does the circle of Zinn supply?
The prelaminar and laminar regions of the optic nerve.
Where do SPCAs form an arterial network?
Within the choroidal stroma.
What artery is a branch of the SPCAs?
The cilioretinal artery.
How many long posterior ciliary arteries are there?
Two.
Where does each long posterior ciliary artery enter the globe?
One laterally and one medially.
What path do long posterior ciliary arteries take?
They travel anteriorly between the sclera and choroid.
What do long posterior ciliary arteries supply?
The ciliary body.
What do the LPCAs form with the anterior ciliary arteries?
The major arterial circle of the iris (in the ciliary body stroma).
How many ethmoid arteries arise from the ophthalmic artery?
Two.
Where do ethmoid arteries travel?
Along the medial wall of the orbit into the ethmoid bone.
Where does the posterior ethmoid artery travel?
It passes through the posterior ethmoid canal in the ethmoid bone.
Where does the anterior ethmoid artery travel?
It passes through the anterior ethmoid canal in the ethmoid bone.
What does the posterior ethmoid artery supply?
Posterior ethmoid sinus, sphenoid sinus, and upper nasal mucosa.
What does the anterior ethmoid artery supply?
Anterior and middle ethmoid sinus, sphenoid sinus, frontal sinus, nasal cavity, and skin of the nose.
Which sinus is NOT supplied by branches of the ethmoid artery?
The maxillary sinus.
Where does the supraorbital artery branch off the opthalmic artery?
Medial to the optic nerve, then courses upward.
What structures does the supraorbital artery supply?
Superior rectus, superior oblique, levator, periorbita, and the skin and muscles of the forehead and scalp.
What are the branches of the muscular artery from the ophthalmic artery?
Lateral and medial muscular arteries.
What does the lateral muscular artery supply?
Lateral rectus, superior rectus, superior oblique, and levator.
What does the medial muscular artery supply?
Medial rectus, inferior rectus, and inferior oblique.
Where do anterior ciliary arteries originate?
From muscular artery vessels supplying the rectus muscles.
What path do anterior ciliary arteries take?
They travel anteriorly toward the limbus.
What are the branches of the anterior ciliary arteries?
They branch into the superficial and deep episcleral vessels.
What do anterior ciliary arteries form in the conjunctiva?
A vascular network in the limbal conjunctiva.
Where do anterior ciliary arteries pierce the sclera?
Just outer to the limbus.
What visible feature may appear when the anterior ciliary arteries pierce the sclera?
Accumulations of pigment such as the axenfeld loop.
What do anterior ciliary arteries supply?
The ciliary body.
What do anterior ciliary arteries anastomose with?
The long posterior ciliary arteries to form the major circle of the iris.
What are the two divisions of the medial palpebral arteries?
Superior medial palpebral artery and inferior medial palpebral artery.
What does the superior medial palpebral artery supply?
The medial upper eyelid.
What does the inferior medial palpebral artery supply?
The medial lower eyelid.
How do medial palpebral arteries enter the eyelids?
They pierce the orbital septum on either side of the medial canthal tendon.
What do medial palpebral arteries anastomose with?
The lateral palpebral arteries to form palpebral arcades in the upper and lower lids.
What do the medial palpebral arteries supply?
Eyelid structures and the medial canthus.
What forms the palpebral arcades?
Anastomoses between medial and lateral palpebral arteries.
How many palpebral arcades are present in each eyelid?
Two, the marginal arcade and the peripheral arcade.
Where is the marginal arcade located?
Near the marginal edge of the tarsal plate.
Where is the peripheral arcade located?
Near the peripheral edge of the tarsal plate.
What do the palpebral arcades supply?
Eyelid structures.
What does the supratrochlear artery supply?
Skin of the forehead and scalp and forehead muscles.
What is the pathway of the supratrochlear artery?
It pierces the orbital septum at the superior medial corner of the orbit and passes with the supratrochlear nerve.
Where does the dorsonasal artery pierce the orbital septum?
Below the trochlea and above the medial canthal tendon.
What does the dorsonasal artery supply?
The lacrimal sac.
Does the external carotid artery significantly supply the globe?
No, only a few branches supply the globe and orbit.
What is the pathway of the external carotid artery?
Passes upward through the neck tissue.
Which branches of the ECA supply the globe/orbit?
Facial artery
Superficial temporal artery
Maxillary artery
“For sure man”
Where does the facial artery arise?
Near the angle of the mandible.
What is the course of the facial artery?
Along the posterior edge of the mandible, curving upward toward the angle of the mouth.
What is the angular artery?
A terminal branch of the facial artery.
What does the angular artery supply?
Lacrimal sac, medial lower lid, and skin of the cheek.
What is the superficial temporal artery?
A terminal branch of the external carotid artery.
What are the branches of the superficial temporal artery?
Anterior temporal artery
Zygomatic artery
Transverse facial artery
“AZ Tea”
What does the anterior temporal artery supply?
Skin and muscles of the forehead.
What does the zygomatic artery supply?
Orbicularis muscle.