Week 11: Choroid and Ocular Blood Supply Flashcards
What is blood?
- It is the fluid in our bodies that maintains life and our existence
- Composed of plasma, platelets, leukocytes (WBCS) and erythrocytes (RBCs)
Describe the aorta
- Beginning at the top of left ventricle & supplies oxygenated blood to circulatory system
- R and L subclavian: arms
- R and L common carotid: neck and brain
- Divides into Internal and External carotid arteries on both sides of the body
What does carotid arteries brach into and what does it supply?
Divides into:
- Internal carotid artery: supplies brain & eye
- External carotid artery: supplies face & neck
What is the internal carotid artery process?
Enter the skull and then traverse the cavernous sinus
- Surrounded by plexus of sympathetic nerves from superior cervical ganglion
- CNII & CNIII accompany the internal carotid as it leaves the sinus
- Ophthalmic artery branches from internal carotid artery as it emerges from the cavernous sinus
Describe cavernous sinus
- Drains blood from the brain
- Located within the middle cranial fossa, on either side of sella turcica of the sphenoid bone
What are the structures transversing the cavernous sinus?
- Oculomotor nerve (CN III)
- Trochlear nerve (CN IV)
- Trigeminal nerve (CNV): ophthalmic (V1) and maxillary (V2) branches
- Abducens nerve (CN VI)
- Internal carotid artery and carotid plexus
Where does each cavernous sinus receive ocular venous drainage from?
- Ophthalmic veins (superior & inferior)
- Central retinal vein
Describe the condition of cavernous sinus thrombosis
- Rare
- Common cause: infection from an extracranial location
- Symptoms: headache, periorbital oedema, proptosis
- Treatment: antibiotic therapy
Describe ophthalmic artery
- Enters orbit within dural sheath of the optic nerve and passes through optic canal
- Primary blood supply to the globe and adnexa
- Branching pattern of the OA is very complicated and unique
What are the major branches of ophthalmic artery?
- Central retinal artery
- Lacrimal artery
- Short & Long Posterior ciliary arteries
- Anterior & Posterior ethmoidal artery
- Supraorbital artery
- Muscular arteries
- Medial palpebral arteries
- Supratrochlear artery
- Dorsonasal artery
Describe Central retinal Artery
- First & smallest branch of ophthalmic artery
- Enters the optic nerve 8-15 mm behind the globe and moves forward within the optic nerve
- Sympathetic nerve plexus surrounds artery
Describe lacrimal artery and their main branches
- Long posterior ciliary arteries
- Muscular branch
- Zygomatic branches
- Lacrimal gland
- Lateral palpebral arteries
- Largest branch ophthalmic artery
- Runs forward to supply lacrimal gland with lacrimal nerve
- Supplies branches to lateral rectus muscle
What is the blood supply to EOM of lacrimal artery?
- Lateral rectus
2. Superior rectus
List the Posterior Ciliary Arteries
- Short Posterior Ciliary Arteries
- Long Posterior Ciliary Arteries
- Cilioretinal (Nasociliary) Arteries
- Anterior Ciliary Arteries
Describe Short Posterior Ciliary Arteries
The major blood flow to the optic nerve head is from:
- Short posterior ciliary arteries
- Peripapillary choroidal arteries
- Circle of Zinn–Haller
Describe Long Posterior Ciliary Arteries
- Run between the sclera and the choroid to the anterior globe
- Enter & supply the ciliary body, branch superiorly, inferiorly and anastamose with Short Posterior Ciliary Artery
Describe Cilioretinal (Nasociliary) Arteries
- As they are separate to the central retinal artery, they also emerge from the disc separately
- Supply the macula
Describe Anterior Ciliary Arteries
- Branches from vessels supplying rectus muscles
- Prior, sends branches to conjunctiva and episclera
- Enters the ciliary body & anastomose with branches of long posterior ciliary arteries forming Major Arterial Circle of Iris
Describe the Ethmoidal Arteries branches and what they supply
- Anterior ethmoidal artery
- Supplies anterior sphenoid sinus, frontal & nasal cavity and skin of nose - Posterior ethmoidal artery
- Supplies the ethmoid sinus and sphenoid sinus
Describe the Supraorbital Artery
- Arises from Ophthalmic artery running upward towards superior EOM
- Supplies skin & muscles of forehead and scalp
What is the blood supply to EOM of supraorbital artery?
- Superior rectus
- Superior oblique
- Levator muscle
Describe Muscular Arteries and what does the lateral/superior and medial/inferior branch supply
Lateral/superior branch supplies:
- Lateral rectus
- Superior rectus
- Superior oblique
- Levator muscle
Medial/inferior branch supplies:
- Medial rectus
- Inferior rectus
- Inferior oblique
List what is in palpebral Arteries
- Marginal Arcades
- Peripheral Arcades
- Anastomose with lateral branches
Describe Supratrochlear Artery
- Supplies the skin and muscles of the forehead and scalp
- Anastomoses with supraorbital artery & external carotid
Describe Dorsonasal Artery
- Sends vessels to supply the lacrimal sac and nose
- Anastomoses with external carotid
What is the blood supply to EOM of infraorbital artery?
- Inferior rectus
2. Inferior oblique
Describe the ocular venous drainage
- Veins have no valves
- Two ophthalmic veins
- Internal venous drainage via vortex veins which drain into ophthalmic veins
Describe the Superior Ophthalmic Vein
- Largest ophthalmic vein,
- Drains blood from: • Anterior and posterior ethmoidal veins • Muscular vein • Lacrimal vein • Central retinal vein • Superior vortex veins
Describe the Inferior Ophthalmic Vein
- Drains blood from: • Inferior and lateral EOM’s • Inferior conjunctiva • Lacrimal sac • Inferior vortex veins
Describe the choroid
- Extremely vascular
- Thin, soft brown coat on inner surface of sclera
- Posteriorly (0.2 mm) & anteriorly (0.1 mm)
List the functions of the choroid
- Nutrition for outer retina
- Secretion of growth factors
- Modulation of IOP
- IOP drainage via uveoscleral pathway
- Pigment cells absorb any excess light
What are the Choroidal Layers?
- Choroidal Stroma (External)
- Choriocapillaris (Middle)
- Bruch’s membrane (Internal)
Describe the choroidal stroma
- Loose connective tissue
- Medium & large blood vessels embedded
- 4 to 5 large vortex veins exit the eye
Describe Choriocapillaris
- Network of capillaries
- Density of capillaries is greatest at the macula
Describe the Bruch’s membrane
- Innermost layer of the choroid
- Molecular sieve regulating the exchange of nutrients & waste products
- Does not contain blood vessels
What are the five layers of Bruch’s membrane
- Basement membrane of choriocapillaris
- Outer collagen fibre layer
- Elastic fibre layer
- Inner collagen fibre layer
- Basement membrane of the retinal pigment epithelium
Describe the choroidal blood supply
- Arterial supply: ophthalmic artery branches from internal carotid artery
- Posterior Ciliary arteries branch from ophthalmic artery to supply choroid
- Venous drainage is via the vortex veins, which drain into the ophthalmic veins
Describe the choroidal nerve supply
- Innervated by long & short ciliary nerves (from CNV, V1)
- Long ciliary nerves innervates: ciliary muscle & iris dilator
- Parasympathetic fibres from ciliary ganglion innervate:
• iris sphincter
• ciliary muscle
• choroidal vessels.
