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Circulation of the head and neck is supplied by
The common carotid artery
The common carotid artery divides the:
Internal carotid artery and External carotid artery
The internal carotid artery supplies
- Structures of the cranium and Eye and related structures
- (supplies blood to the eye)
The external carotid artery supplies:
- Superficial areas of the head and neck
- Small portion of the circulation to the ocular adnexa
Internal carotid artery- 3 things
- 1- Enters the skull through the carotid canal
- 2- Then immediatly enters the cavernous sinus
- 3- As it emerges, it branches to the opthalmic artery (fist major branch)
The first branch of the Internal Carotid Artery:
The Opthalmic Artery
Opthalmic Artery - 4 things
- 1- Enters the orbit within the dural sheath of the optic nerve
- 2- Passes through the optic canal (below and lateral to the nerve)
- 3- In the orbit it runs inferolateral to the optic nerve for a short distance
- 4- Then crosses either above or below the nerve (20% below)
9 Opthalmic Artery Branches
- 1- Central Retinal Artery
- 2- Lacrimal Artery
- 3- Ciliary Arteries - 2
- 4- Ethmoid arteries - 2
- 5- Supraorbital Artery
- 6- Muscular Arteries - 2
- 7- Sup and Inf Medial Palpebral arteries
- 8- Supratrochlear artery
- 9- Dorsonasal artery
Central Retinal Artery - 4 things
- 1- The smallest branch
- 2- Leaves the opthalmic artery as it lies below the optic nerve
- 3- Enters the meningeal sheath of the nerve about 10-12 mm behind the globe
- 4- Supplies the inner retina
Central Retina Artery info
- In the optic nerve, the CRA provides the collateral branches ( to the nerve and pia mater)
- The CRA passes through the lamina cribose and enters the optic disk nasal to center branching into the Superior and Inferior.
- The S and I branches divide further into nasal and temporal branches
- These vessels continue to bifurcate
- 2 capillary networks are formed, the deep capillary plexus and the Superficial capillary plexus
- No blood vessels are found in the macula or fovea
Orgion of Posterior Ciliary Arteries
The Opthalmic Artery from the Internal Carotid Artery
Posterior Ciliary Artery Branches
- Short Ciliary Arteries (10-20)
- Long Ciliary Arteries (2)
Short Posterior ciliary arteries info:
- Arise as one or two branches, then form 10-20 branches
- Enter the scelera in a ring around the optic nerve and from the arterial network within the choroidal stroma
- Divide to form posterior choriocapillaris
- Other branches form the Circle of Zinn
- Supplies the Optic nerve of the head (external part of retina)
Job of posterior choriocapillaries
Nourishes retina as far anteriorly as equator
Circle of Zinn
Encircles the optic nerve at the choriod
Where does almost the entire blood supply of the eye (minus the inner retina) come from:
The uveal vessels
Long Posterior Cilliary Arteries
- One enters nasally one temporally
- Near the optic nerve
- Give 3-5 branches at the ora serrata and passes directly back to form the anterior choriocapillaris.
- These capillaries nourish retina from the equator forward.
- Run between the sclera and choroid anterior globe.
- Enter the ciliary body and branch superiorly and inferiorly
- Anastomose with each other and with the anterior ciliary arteries and form the major arterial circle of the iris.
Major arterial circle of the iris
- Located in the ciliary stroma
- Is the source of the radial vessels found in the iris
Long Anterior Ciliary Arteries
- Branch from the vessels that supply the rectus muscles
- Exit the muscles near the insertions, run along the tendons
- Then loop inward to pierce the sclera (just outer to the limbus)
- Before entering the scelera, they send branches into the conjunctiva, forming a network of vessels in the limbal conjunctiva.
- Other branches enter the episcelera to form a network of vessels before entering the uvea, then enter the ciliary body and anastomose with the branches of the long posterior ciliary arteries (major circle of the iris)
- Generally, 2 emanate from each of the rectus muscles, wih exception of the lateral muscle (only 1)
Anterior Ciliary Arteries supply blood to
The conjunctiva, episclera, ciliary body, and iris
Venous drainage by the Radial episcleral collecting veins
- Receive blood from the anterior conjuntiva, limbal archades, anterior episcleral veins, and perforating scleral veins.
- Then form the anterior ciliary veins (leave the globe anteriorly over the rectus muscles)
Vortex veins drainage
Posteriorly 4-7 vortex veins drain the venous system ( the choriod, cilary body, and iris) into the superior and inferior opthalmic veins
The Central Retinal Vein:
- 33% larger then CRA
- Drains into the superior opthalmic vein and/or the cavernous sinus
Blood flow through the blood vessel depends on:
The perfusion pressure (PP), the pressure that drives blood through the vessel, and the resistance (R) generated by the vessels.
Ocular pressure can be reduced by either:
Reduction of arterial pressure or increase in intraocular pressure.
That property of a vascular bed that permits constant or nearly constant blood flow throughout a wide range of perfusion pressures
Blood flow in the retina appears to be controlled by:
Primary metabolic needs, especially the need for oxygen
When O2 levels are low it leads to:
More blood production
When there is less O2, what happens
When there is too much O2
Ones that maintain the body in rest
- Used to make body aware for emergencies
- - Lowers the blood flow
Blood flow formula
P arteries (intering tissue) - P veins (leaving tissue)/ Resistance
What is the mean arterial pressure of the arteries entering the eye?
What is the pressure of the episcleral veins leaving the eye?
- The numeric value that indicates how easily blood can pass through a tissue.
- Is approx 50 mmHg (diff between A and veins)
What value is being used in glaucoma research?
- - Research is showing that glaucoma patients with low OPP are 1.5 x more likely to develop progressive nerve damage from ischemia.
- Ocular perfusion pressure
- Diastolic bp-intraocular bp
Acute angle closure attack
- High IOP will infringe on CRA which leads to:
- reduction in blood supply to the retinal tissue and:
- retinal vessels increase their vessel diameter to allow more blood flow (autoregulation).
If IOP is high enough for a long time:
CRA will obtain its critical closing pressure and shut down.
Pressure at which a blood vessel collapses and blood flow stops:
Critical closing pressure
What happens in acute closure attack?
IOP increases- which reduces the artieral pressure entering the retina
If IOP remains elevated for a long enough perior of time:
CRAO occurs, PP decreases = hypoxia retina
What is the primary threat to vision loss in an acute angle closure attack?
CRAO- Central Retinal Artery Occlusion
Pressure in the ocular veins (outside the eye) is lower than what?
- To drain into the trabecular meshwork and into the venous system.
IOP is lower then what?
- The perfusion pressure of the retinal and uveal arteries.
- Allows nutrients to be delivered from the choriocapillaris to the retina.
- Capillaries that contain pores that span the endothelial lining,
- These pores permit the rapid exchange of water and solutes
- The majority of blood flow in the ocular vessels is always in the choriocapillaris (60%)
- Capillaries have huge fenestration- they provide the outer retina with oxygen, glucose, vitamen A, etc.
Has Fenestrated capillaries
Iris and renal capillaries are non-fenestrated
- Arise either from the vessels entering the choriod or from the Circle of Zinn.
- Arise from the ciliary circulaton and not from the retinal supply
- Occur 15-50% of the population
- Supply the macular area
- ORA direct blood supply to the macular area will be maintained in those individuals with such a cilioretinal artery
Retinal blood flow has what 2 things?
- Dual blood supply
- Blood retinal barrier
Dual blood supply
- Central retinal artery= inner retina
- Choriocapilaris (choriod)= outer retina
Blood Retinal Barrier
Barrier formed by tight junctions between endothelial cells lining the retinal vessels as well as between RPE cells.
What does keeping the blood of the choriocapillaris out of the retina do?
Prevents damage cause blood is toxic to the retina
Retinal blood supply
- Vessel walls are transparent (colomn of blood within the vessel can be seen)
- Lighter colored blood is the oxygenated blood of the artery.
- Venous deoxyenated blood is slightly darker.
- The artery generally lies superficial to the vein
What predispose thrombus formation in the CRV?
This anatomical position predisposes to thrombus formation in the CRV by various factors, including slowing the blood stream, changes in the vessel wall, and changes in the blood.
Inflammations in the Anterior Ciliary Artery generate:
An increase of the blood supply to the affected areas, causing hyperemia.
Anterior Ciliary Artery Inflammations
- The superficial blood vessels are injected, giving the conjunctiva a bright red color that often increases toward the fornix.
- The vessels move with conjunctivial movement and can be blanched with a topical vasoconstrictor.
- The deeper scleral and episcleral vessels are injected, giving the circumlimbial area a pirplish or rose-pink color
- These vessels fo not move with the conjunctiva and are not blanched with a topical vasoconstrictor.
ANS system control
By Sympathetic and Parasympathetic Innervation
- Vasoconstriction of the blood vessels
- Maintaining a resonable blood flow through the uvea during sudden spikes in blood pressure.
- Helps autoregulation to maintain the intraocular flow and constant volume.
- Vasodilation of the blood vessels
- Maitains high ocular blood flow during loss of systemic blood pressure.
- Mediates increase blood flow in response of increase retinal activity.
The Cranial Nerves
- 12 pairs
- The nucleus are found in the brain stem, except 1st and 2nd pair.
- Some are Sensoral, some Motor, some Both
The Brain stem
- The midbrain, the pons, and the medulla oblongata
- Lies over the basilar portion of the occipital bone, with slight inclination
Cranial nerves w/ optometric importance
- Optic, Occlomotor, Trochlear, Trigeminal, Abducens, Facial, Vestibularcochlear
The facial nerve
- Mostly a motor (efferent) nerve, but has parasympathetic innervation and some sensorial (affarent) functions
- The Sensoral functions are in the anterior 2/3 of tongue.
Facial nerve supplies afferent innervation to where?
To the oropharynx below the palantine tonsil. There is also a small amount of cutaneous sensation carried by the nervous intermedius from the skin in and around the auricle.
The facial nerve helps in providing Parasympathetic Innervation to where?
- The lacrimal gland, the submandibular, and sublingual salivatory glands, increasing their production
- Also to the glands of the eyelids (tarsal glands) and inhibits the tarsal muscles.
Main function of the facial nerve
Motor control of most of the muscles of facial expression. It also innervates the porsterior belly of the digastric muscle, the stylohyoid muscle, and stapedius muscle.
Nucleus of Origion of the FN
Inside the pons of the brain stem, close related to the superior salivatory nucleus.
The FN has what type of neurons
The salivatory nucleus has what type of neurons?
Parasympathetic preganglionic neurons (which are also efferent) and some afferent neurons related to the Glossopharyngeal nerve nucleus,
Where does the FN exit?
- At the Ponto-medullary junction, lateral to the Abducens nerve and medual to the 8th CN.
- Between these two, the axons from the salivatory nucleus is called the Nervous intermedius.
The nervous intermedius is composed of?
Preganglionic parasumpathetic fibers and some afferent fibers.
- Exits the interior of the pons, and enters the geniculate ganglion. After it leaves this ganglion, it contains the fibers of the nervous intermedias, and they travel together.
- Inside the skull, It enters the internal aucostic meatus of the petrous portion of the temporal bone, and gives several branches- the main one being the Greater Petrosal Nerve.
- The Greater Petrosal nerve exits the skull and enters into the Pterygopalantine ganglion.
What is the Greater Petrosal Nerve known as?
The vidian nerve
The pterygopalatine gangion is known as what 2 things
The sphenopalatine ganglion and Meckel's ganglion
The vidian nerve is made of ?
- Pre-ganglionic parasympathetic fibers from the superior salivatory nucleus.
- These fibers synapse with neurons found in the Meckel's ganglion.
- The neurons then produce post-ganglionic parasympathetic fibers.
The facial nerve exits the interior of the petrous temporal through what and gives what 5 branches.
- The Sytlomastoid
- - Temporal, Zygomatic or Malar, Buccal, Mandibular, Cervical.