Week 11: Eye, Orbit and Lacrimal Apparatus, Ear Flashcards by Mhairi Wan

walls of the orbit

roof
lateral wall
medial wall
floor

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The margins of the orbit are formed by what three bones

frontal bone superiorly
the zygomatic bone laterally
maxillainferomedially

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what bones form the roof, floor and lateral walls of the orbit

roof = frontal
floor = maxilla
lateral = zygomatic

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what are the bones of the orbit

frontal
maxilla
lacrimal
palatine
zygomatic
ethmoid
greater and lesser wing of the sphenoid

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what are the Openings into the Orbit

superior and inferior orbital fissure
nasolacrimal canal
optic canal

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contents of the orbital openings

Inferior orbital fissure - inferior ophthalmic vein
Optic canal- the ophthalmic artery and the optic nerve
The superior orbital fissure - superior ophthalmic vein + CN III, IV, V1, VI

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Orbit: Structure & Contents

Optic nerve (CN II) with central retinal artery & vein (end/terminal artery)
Eyelids & lacrimal apparatus
Extraocular muscles - superior and inferior rectus
Retrobulbar fat in the orbit supporting the eyeball

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what are the clinical implications of a pituitary tumour in regards to eye sight

optic nerves enter the skull meet & form the optic chiasm that lies just superior & anterior to the pituitary gland/ sella turcica.
Due to the vicinity of both structures, some pituitary tumours can press onto optic chiasm causing visual field issues anda symptom which is frequently expressed by patients as tunnel vision

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structure of the optic nerve

## Central retinal vein and artery in the middle of the section

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what happens when the central retinal artery sometimes become occluded

Can be due to either transient or permanent causes
Occlusion tends to lead to loss of vision
- Temporary case = amaurosis fugax - painless temporary loss of vision in the affected eye
- there can also be permanent loss of vision due to occlusion

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what are the three meningeal layers surrounding the optic nerve

the dura mater
arachnoid
pia mater
+ subarachnoid space between the arachnoid and the pia which is filled with CSF

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what is papilloedema

Raised intracranial pressure is transmitted to the meninges & subarachnoid space around the optic nerve (CN II) that slows retinal venous drainage via the central retinal vein

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what are the 3 main hemianopias

injury affecting the optic nerve on one side. the sight to that eye will be lost, the other eye is still working fine.
an issue at the optic chiasm, and this is where we are coming back to the pituitary tumour pressing on the optic chiasm, and the resultant tunnel vision. lateral side of each visual field is lost if information can no longer pass across the optic chiasm = bitemporal hemianopia
a lesion to the optic tract on the left side, and this means that the parts of the visual field supplied by this tract will not work, which is the medial side on the affected side, and the lateral side on the right side

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Orbicularis Oculi Muscle

orbital part around the orbit
a palpebral part which goes into the eyelids.

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where are tears produced

in the Lacrimal gland in upper lateral corner of the orbit

Tears are secreted into the conjunctival sac & continually washed across the eye by blinking of the eyelids

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how are tears drained

lacrimal puncta –> ducts called canaliculi –> the lacrimal sac –> nasolacrimal duct which runs within the nasolacrimal canal –> inferior nasal meatus in the nasal cavity

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parasympathetic supply of lacrimal gland (stimulation of production of tears)

PRE
= via CNVII nervus intermedius –> greater petrosal + deep petrosal = nerve of pterygoid canal –> pterygopalatine ganglion
POST
= hitchhike with zygomatic CNV2 and lacrimal of CNV1
–> lacrimal gland

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sympathetic supply of lacrimal gland (regulate constriction)

superior cervical ganglion via internal carotid plexus and deep petrosal nerve

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extraocular muscles

recti = the superior, medial, lateral, and inferior rectus
2 obliques = the superior and inferior
(& levator palpebrae superioris)

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Extraocular Muscles: motor nerve supply

CNIII
- medial rectus
- inferior rectus
- inferior oblique
- superior rectus
- levator palpebrae superioris
CN IV
- superior oblique,
CN IV
- lateral rectus

LR6 SO4 AO3

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Injury to the oculomotor nerve (CN III) will remove the parasympathetic pupil constriction leading to

dilated pupil (mydriasis)
ptosis (complete loss of levator palpebrae superioris) & the eye is turned downwards & outwards (superior oblique & lateral rectus are intact)
= oculomotor palsy

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layers of the eyeball

sclera, the outermost, fibrous layer
choroid, the vascular layer
the innermost layer, the retina

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how is the lens able to focus to accommodate different visual stimuli

enabled by the ciliary muscle and the fibres which attach the ciliary body to the lens

zonular fibres connect ciliary body to the lens
- dependent on whether the zonular fibres are under tension (far) or relax (near) = control proximity of vision

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what control is the dilator pupillae under

sympathetic control

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what control is the sphincter pupillae under

parasympathetic control

what houses the vestibulo-cochlear apparatus

petrous temporal bone

the ear is divided into what 3 parts

external middle internal

what separates the external ear from the middle ear

the tympanic membrane

what joins the middle ear to the nasopharynx

pharyngotympanic/auditory/Eustachian tube

what does the external ear consist of

the auricle external acoustic meatus = composed of cartilage & bone leading sound waves to the tympanic membrane

what is the hearing process

the auricle and external acoustic meatus capture sound waves and direct them to the tympanic membrane

what does the middle ear consist of + function

- 3 bony ossicles mechanically transmitting sound through their movement - it is connected to pharynx by the auditory tube - it allows for air to enter the middle ear

what does the internal ear consist of

Vestibulocochlear organ - contains the membranous labyrinth, which in turn is suspended in the bony labyrinth. The bony labyrinth includes the semicircular canals, the cochlea, and the vestibule

what is the visible part of the ear called

the auricle/pinna

what is the function of the auricle( external ear)

has a supportive function - facilitates hearing = it catches and funnels sound first into the external acoustic meatus and then to the tympanic membrane and inner ear

what is the sensory innervation of the skin of and around the external ear

the greater auricular nerve (middle, post lat) the auriculotemporal nerve (ant lat)

what is the sensory innervation of the skin of and around the external ear

the great auricular nerve (middle, post lat) the auriculotemporal nerve (ant lat)

what is the structure of the External acoustic meatus

- About 2.5cms long - has a cartilaginous lateral 1/3rd - bony medial 2/3rds - in middle contains skin, hair follicles and ceruminous glands - produce ear wax)n

what is the tympanic membrane

thin, oval semitransparent membrane at the medial end of the external acoustic meatus it forms a partition between the external acoustic meatus and the tympanic cavity of the middle ear,

where is the tympanic membrane

held in the temporal bone by fibrocartilaginous

what are the muscles of the middle ear

the tensor tympani stapedius

what are the parts of the auditory ossicles

malleus - connected to tympanic membrane incus stapes - base lies in fenestra vestibuli

oval opening on the wall of the tympanic cavity is the

oval window/ fenestra vestibuli - it leads to the vestibule of the bony labyrinth of the inner ear

what is the ossicles function in the hearing process

increase the force and decrease the amplitude of the vibrations from the tympanic membrane

function of the auditory tube

pressure equalisation and to replenish the air of the middle ear

what is the side effect of this connection (middle ear - nasopharynx

infections can enter the middle ear through the same pathway, and this is why respiratory tract infections can sometimes cause middle ear infections as well

What is a Schwannoma and its significance

benign tumour of a type of nerve cell, affecting the vestibulocochlear nerve and the surrounding tissue through its growth can potentially endangers the facial nerve (due to its close proximity) Surgery = to remove internal acoustic meatus

what is the significance about ear infections

- the internal carotid artery and internal jugular vein run very close to the ear - thin roof of bone between middle ear & middle cranial fossa - mastoid air cells, very close to the middle ear and connected via mastoid antrum - mucous membrane which lines the mastoid air cells, the tympanic cavity, and the auditory tube is continuous = there is a risk that infections from the middle ear might spread into the cranial cavity. = if the infection is very severe, it can spread and erode through the bone and affect the vascular structures, and spread further through the systemic circulation. = mastoiditis

Middle ear infections are called

Oits media

what happens when you get CHRONIC OTIS MEDIA

Risk of damage to the ossicles causing conductive hearing loss = issue is with the transmission of sound mechanically via the ossicles rather than with the CN VIII these may spread to the mastoid air cells (mastoiditis) or beyond

common cause of otis media

often caused by obstruction to the auditory tube

what is the fluid in the bony labyrinth

perilymph within which the membranous labyrinth is suspended that contains endolymph

what is the bony labyrinth

is the fluid-filled space surrounded by the otic capsule (part of the petrous temporal bone)

what are the cavities of the bony labyrinth

the vestibule, the semicircular canals, and the cochlea

Where and what does CNVIII divides into

near the lateral end of the internal acoustic meatus: a cochlear nerve and a vestibular nerve

what is the the Vestibular labyrinth concerned with + innervation

balance and equilibrium CNVIII - vestibular nerve

what is the the Cochlear labyrinth concerned with + innervation

hearing CNVIII cochlear nerve

what is the The vestibulocochlear apparatus

CN VIII, the cochlea, semicircular canals, the saccule, and the utricle

what does the the cochlear part CNVIII supply

cochlea

what does the the vestibular part CNVIII supply

it sends branches to the semicircular canals, the saccule, and the utricle = structures within or connected to the vestibule.

what is neural hearing loss

damage to the cochlear part of CN VIII the problem is with the nerve and the transmission of information through the nerve, or with the cochlea generally

what is conductive hearing loss

problem with mechanical transmission of sound = issues affecting the movement of the ossicles.

what causes - ataxia, vertigo and nausea.

injury or damage to the vestibular part of CN VIII

what nerves provide general sensory innervation to the meatal side of tympanic membrane.

The auriculotemporal nerve (branch of CN V3) the vagus nerve (CN X)