optic nerve and opthalmic artery

8/7/2019 Optic nerve and opthalmic artery

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Optic nerve and opthalmic artery


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Cranial Nerve II: Optic

y Arises from the retina

of the eye

y Function: sensory -

solely for visiony Exits through optic

canal


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y The optic nerve is the second cranial nerve

y It arises from the optic chiasma on the floor of the diencephalon

y Enters the orbit through the optic canal, accompanied by the

ophthalmic artery

y It changes its shape from being flattened at the chiasma to

rounded as it passes through the optic canal

y Nerve is extension of brain covered by meninges

y Length: 4 cm ; 2.5 mm intraorbital and 5 mm intracanalicular

and 10 mm intracranial

yIn the orbit it passes forwards, laterally and downwards, andpierces the sclera 3mm medial to the posterior pole

y It has a somewhat tortuous course within the orbit to allow for

movements of the eyeball


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y Special somatic afferents (SSA) are found only in supraspinal locationsand are represented by the laterally-lying vestibular and auditory nucleiin the medulla and pons.

y They develop from branchial arch structures.

Cranial nerves I and II serve vision (SSA) and olfaction (SVA)

y However, these are not true nerves.

y Rather they develop as evaginations of the telencephalon (olfactorynerve) and the diencephalon (optic nerve)

y I I(optic) SSA:

y Originates in ganglion cells of retina

y Lateral geniculate nucleus and superior colliculus


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y The optic nerve or nerve of sight, consists mainly of fibers

derived from about 1.2 million ganglionic cells of the retina

y These axons terminate around the cells in the lateral geniculate

body, pulvinar, and superior colliculus which constitute the loweror primary visual centers

y From the cells of the lateral geniculate body and the pulvinar

fibers pass to the cortical visual center, situated in the cuneus and

in the neighborhood of the calcarine fissure

y There are also a few fine fibers, afferent fibers, extending from

the retina to the brain, that are supposed to be concerned in

pupillary reflexes


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Relationsy The optic nerve has important relationships with other orbital structure

y As it leaves the optic canal, it lies superomedial to the ophthalmic artery,and is separated from lateral rectus by the oculomotor, nasociliary and

abducens nerves, and sometimes by the ophthalmic veins

y The optic nerve is closely related to the origins of the four recti muscles,

whereas more anteriorly, where the muscles diverge, it is separated fromthem by a substantial amount of orbital fat

y Just beyond the optic canal, the ophthalmic artery and the nasociliary

nerve cross the optic nerve to reach the medial wall of the orbit


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y The central artery of the retina enters the substance of the optic

nerve inferomedially about 1.25 cm behind eye ball

y Near the back of the eye, it becomes surrounded by long andshort ciliary nerves and vessels


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y Medial palpebral branch: supply eyelids

y Dorsal nasal branch supply upper part of nose

y Optic nerve has no neurilemmal sheathy It has no power of regeneration

y It is tract

y Optic nerve atrophy is damage to the optic nerve

y The optic nerve can also be damaged by shock, various toxic

substances, radiation, and trauma


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Opthalmic artery

y The main vessel supplying orbital structures is the

ophthalmic artery

y Its terminal branches anastomose on the face and scalp with

those of the facial, maxillary and superficial temporalarteries,

y Establishing connections between the external and internal

carotid arteries

y

In addition to the ophthalmic artery, the infraorbital branchof the maxillary artery, and possibly the recurrent meningeal

artery, supply orbital structures


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y The ophthalmic artery leaves the internal carotid artery as it

quits the cavernous sinus medial to the anterior clinoid process

y It enters the orbit by the optic canal, inferolateral to the opticnerve

y It crosses between the optic nerve and superior rectus to reach

the medial wall of the orbit, running between superior oblique

and medial rectus.

y At the medial end of the upper eyelid, it divides into

supratrochlear and dorsal nasal branches


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y As it crosses the optic nerve with the nasociliary nerve, it is

separated from the frontal nerve by superior rectus and levator

palpebrae superiorisy In c.15% of subjects the ophthalmic artery crosses below the

optic nerve

y It has the following branches:

y Central artery of the retina, lacrimal artery, muscular branches,ciliary arteries, supraorbital artery, posterior ethmoidal artery,

anterior ethmoidal artery, meningeal branch, medial palpebral

arteries, supratrochlear artery, dorsal nasal artery


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y Central artery of the retina :The small central artery of the

retina is the first branch

y It begins below the optic nerve and for a short distance

y it lies in the dural sheath of the nerve

y It enters the inferomedial surface of the nerve c.1.25 cm behind

the eye

y Runs to the retina along its a muscular branches

y The central retinal artery supplies all the nerve fibers that form

the optic nerve


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y There are three groups of ciliary arteries: long and short posterior, and

anterior

y Long posterior ciliary arteries, usually two, pierce the sclera near the optic

nerve, pass anteriorly along the horizontal meridian and join the greaterarterial circle in the iris

y About seven short posterior ciliary arteries pass close to the optic nerve to

reach the eyeball where they divide into 15-20 branches

y T

hey pierce the sclera around the optic nerve to supply the choroid, andanastomose with twigs of the central retinal artery at the optic disc

y Anterior ciliary arteries :They reach the eyeball on the tendons of the recti,

form a circumcorneal subconjunctival vascular zone, and pierce the sclera

near the sclerocorneal junction to end in the greater arterial circle of the iris


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y The lacrimal artery is a large branch which usually leaves the

ophthalmic artery near its exit from the optic canal

y It accompanies the lacrimal nerve along the upper border of

lateral rectus, supplies and traverses the lacrimal gland, and

ends in the eyelids and conjunctiva as the lateral palpebral

arteries

y Lacrimal artery gives off one or two zygomatic branches

y One reaches the temporal fossa via the zygomaticotemporalforamen, and anastomoses with the deep temporal arteries.

y The other reaches the cheek by the zygomaticofacial

foramen, and anastomoses with transverse facial arteries

y A recurrent meningeal branch, usually small, passes back via

the lateral part of the superior orbital fissure to anastomosewith a middle meningeal branch


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y The supraorbital artery leaves the ophthalmic artery where it crosses

the optic nerve

y Ascends medial to superior rectus and levator palpebrae superioris

y It passes through the foramen and divides into superficial and deep

branches which supply the skin, muscles and frontal periosteum

y It supplies superior rectus and levator palpebrae superioris, and sends

a branch across the trochlea to the medial canthus

y The posterior ethmoidal artery runs through the posterior ethmoidalcanal and supplies the posterior ethmoidal air sinuses


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y The anterior ethmoidal artery passes with its accompanyingnerve through the anterior ethmoidal canal to supply ethmoidal

and frontal air sinusesy The supratrochlear artery is a terminal branch of the ophthalmic

artery

y It leaves the orbit superomedially with the supratrochlear nerve,

ascends on the forehead to supply the skin, muscles andpericranium, and anastomoses with the supraorbital artery andwith its contralateral fellow


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Applied

y Optic neuritis is inflammation of the optic nerve.

y It may cause sudden, reduced vision in the affected eye

y Sudden inflammation of the nerve connecting the eye and the

brain (optic nerve) can injure the insulation surroundingeach nerve fiber, causing the nerve to swell


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y Optic neuritis most commonly develops due to an autoimmune

disorder that may be triggered by a viral infection, vitamin B

deficiency

y Ocular stroke commonly is caused by embolism of the retinal artery

y Retinal artery occlusion represents an ophthalmologic emergency, and

delay in treatment may result in permanent loss of vision

y Acutely, obstruction of the central retinal artery results in inner layer

edema and damage of the ganglion cell nuclei


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y The ciliary ganglion is a parasympathetic ganglion which is concernedfunctionally with the motor innervation of certain intraocular muscles

y It is a small, flat, reddish-grey swelling, 1-2 mm in diameter,connected to the nasociliary nerve,

y located near the apex of the orbit in loose fat c.1 cm in front of themedial end of the superior orbital fissure

y It lies between the optic nerve and lateral rectus, usually lateral to theophthalmic artery

y Its neurones, which are multipolar, are larger than in typicalautonomic ganglia; a very small number of more typical neurones arealso present


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y Its connections or roots enter or leave it posteriorly

y Eight to ten delicate filaments, termed the short ciliary nerves,emerge anteriorly from the ganglion arranged in two or three bundles,the lower being larger

y They run forwards sinuously with the ciliary arteries, above and belowthe optic nerve, and divide into 15-20 branches

y Pierce the sclera around the optic nerve and run in small grooves onthe internal scleral surface

y They convey parasympathetic, sympathetic and sensory fibres betweenthe eyeball and the ciliary ganglion: only the parasympathetic fibressynapse in the ganglion

optic nerve and opthalmic artery

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