Session 8 - functional anatomy and disorders of the eye

Question 1

what are the borders of the orbital cavity

Answer 1

Roof (superior wall) – Formed by the frontal bone and the lesser wing of the sphenoid. The frontal bone separates the orbit from the anterior cranial fossa.
Floor (inferior wall) – Formed by the maxilla, palatine and zygomatic bones. The maxilla separates the orbit from the underlying maxillary sinus.
Medial wall – Formed by the ethmoid, maxilla, lacrimal and sphenoid bones. The ethmoid bone separates the orbit from the ethmoid sinus.
Lateral wall – Formed by the zygomatic bone and greater wing of the sphenoid.
Apex – Located at the opening to the optic canal, the optic foramen.
Base – Opens out into the face, and is bounded by the eyelids. It is also known as the orbital rim

Question 2

what are the three openings at the apex of the orbital cavity transmitting blood vessels and nerves into and out of the orbit

Answer 2

superior orbital fissure
inferior orbital fissure
optic canal

Question 3

what feature of the orbit conveys some protection to the structure

Answer 3

the tough orbital rim

Question 4

what is the weakest part of the orbit

Answer 4

the medial wall and the floor of the orbit

this is because of the paranasal air cavities (maxillary and ethmoid)

Question 5

what are the paranasal sinues

Answer 5

air-filled extensions of the respiratory part of the nasal cavity. There are four paired sinuses, named according to the bone in which they are located; maxillary, frontal, sphenoid and ethmoid.
they may contribute to the humidifying of the inspired air. They also reduce the weight of the skull.
As the paranasal sinuses are continuous with the nasal cavity, an upper respiratory tract infection can spread to the sinuses. Infection of the sinuses causes inflammation (particularly pain and swelling) of the mucosa, and is known as sinusitis. If more than one sinus is affected, it is called pansinusitis.

The maxillary nerve supplies both the maxillary sinus and maxillary teeth, and so inflammation of that sinus can present with toothache.

Question 6

what are the symptoms of an orbital blow out fracture

Answer 6

• Periorbital swelling, painful
• Double vision (especially on vertical
gaze)
• Impaired vision
• Anaesthesia over affected cheek (upper teeth and gums) on affected
side
• limited movement of eyeball- eye can’t look up as muscle is nicked
symptoms occur because the infraorbital nerve which is a branch of the trigeminal nerve runs along the floor of the orbit and provides sensory innervation to the cheek

Question 7

what happens in an orbital blow out fracture

Answer 7

Sudden increase in intra-orbital pressure (e.g. from retropulsion of eye ball [globe] by fist or ball) fractures floor of orbit (weakest part)
Orbital contents and blood can prolapse into maxillary sinus; the fracture site can ‘trap’ structures e.g. soft tissue, extra orbital muscle located near floor or orbit

Question 8

what features on an x-ray may indicate an orbital blow out fracture

Answer 8

tear drop sign- fracture of the floor of the orbit -shadow of tissue prolapsing down from orbital floow
fluid level - as blood accumulates
black maxillary paranasal air sinus- as it is full of air

Question 9

what are the contents of the eyelids (palpebrae)

Answer 9

– Protect the eye when palpebral fissure is closed
– Tarsal plates and muscles
– Glands at the edges of the eyelids

Question 10

what are the contents of the orbital cavity

Answer 10

– Lacrimal apparatus
– Nerves and blood vessels
– Orbital fat (lots!)
– Globe of the eye (eyeball) and its internal structures
– Extrinsic ocular muscles (extra-ocular)
• Muscles that move the
eyeball

Question 11

what is the orbital septum

Answer 11

is a thin sheet of fibrous tissue originating from orbital rim
– Blends with tendon of LPS and tarsal plates
• Orbital septum separates intra-orbital contents from eyelid fat and orbicularis oculi muscle
• Acts as a barrier against infection spreading from the pre-septal space
to post-septal (orbital cavity proper)

Question 12

what is the function of the tarsal plate

Answer 12

provides a connective tissue skeleton to the eyelid

– Firmness and shape

Question 13

what is pre-septal orbital cellulitis

Answer 13

Infection in front of membrane Orbital septum prevents it going into orbital cavity
Localised to eyelids

Question 14

what is post-septal orbital cellulitis

Answer 14

Deep inside orbital cavity
If infection spreads behind orbital septum most concerning
Redness and
swelling much more
diffused
Deeper inside the
eye

Question 15

what are the potential complications of periorbital cellulitis

Answer 15

Complications include abscesses formation and spread of infection
intracranially- cavernous sinus thrombosis
Veins of orbit drain to cavernous sinus,
pterygoid venous plexus and facial veins

Question 16

what are meibomian glands

and what happens when they get blocked

Answer 16

a special kind of sebaceous gland at the rim of the eyelids inside the tarsal plate, responsible for the supply of meibum, an oily substance that prevents evaporation of the eye’s tear film and tear spillage

Question 17

what happens if a meibomian gland gets blocked up

Answer 17

you get a meibomian cyst

Question 18

why do you get a stye

Answer 18

when eyelash follicles block they can get infected with staph

Question 19

how do you treat meibomian cysts and styes

Answer 19

Treat conservatively
Give hot compresses to unblock glands to release contents
Watch and wait
Surgical incise if had for very long time

Question 20

what is the conjunctivae of the eye

Answer 20

Conjunctivae (transparent mucous membrane) that produces mucous and tears to lubricate the conjunctival and corneal surfaces
Covers white of eye (sclera) and lines inside of eyelids
(forming a conjunctival sac); does not cover over cornea
Highly vascular with small blood vessels within the
membrane

Question 21

what is the lacrimal apparatus

Answer 21

involved in
secretion of tears into conjunctival sac
– Lacrimal gland (arranged around edge of levator palpebrae superioris)
– Lacrimal sac
– Nasolacrimal duct

Question 22

why do we blink

Answer 22

Blinking washes tear film across front of eye, rinsing and lubricating the conjunctivae and cornea

Question 23

what is conjunctivitis

Answer 23

inflammation of the conjunctiva of the eye (pink eye) can be caused by infection or allergies

Question 24

what is the main arterial supply to the orbit

Answer 24

opthalmic artery which is branch of the ICA

Question 25

what is the venous drainage of the orbit

Answer 25

Ophthalmic veins which drain venous blood into cavernous sinus, pterygoid plexus and facial vein

Question 26

which nerve provides general sensory to the eye (including conjunctiva and cornea)

Answer 26

opthalmic division of trigeminal Va

Question 27

which nerve provides special sensory vision from retina

Answer 27

optic nerve

Question 28

which motor nerves supply the muscles of the orbit

Answer 28

occulomotor trochlea abducens

Question 29

what maintains the position of the eyeball (the eyeball does not sit on the orbital floor)

Answer 29

– Suspensory ligament (sits underneath like a sling) – Rectus muscles – Orbital fat

Question 30

what are the three layers of the eyeball

Answer 30

– Outer: fibrous, tough sclera (white of eye) continuous anteriorly as transparent cornea* – Middle: vascular consisting of choroid, ciliary body and iris – Inner: retina (inner photosensitive layer lying on an outer pigmented layer- prevents scattering of light)

Question 31

where is the anterior chamber found and what is found within the anterior chamber

Answer 31

it is found between the cornea and the iris | aqueous humour

Question 32

where is the posterior chamber found and what is found within the anterior chamber

Answer 32

it is found between the iris and the lens | aqueous humour

Question 33

how does the pupil adjust its size

Answer 33

muscles of iris constrict and dilate under autonomic control to adjust the size of the pupil

Question 34

why is the cornea avasular

Answer 34

must be transparent for light to get through

Question 35

what is found within the vitreous chamber

Answer 35

vitrous humour

Question 36

what happens when the ciliary body receives PS innervation

Answer 36

causes them to contract and move inward - muscles move in so tension in the ligaments suspending the lens to the ciliary body decreases and the lens gets fatter

Question 37

what is your blind spot also know as

Answer 37

optic disc

Question 38

what is the most common cause of blindness

Answer 38

Age-related macular degeneration

Question 39

what produces aqueous humour

Answer 39

by ciliary processes within ciliary body in the posterior chamber it flows from the posterior chamber to the anterior chamber to nourish the lens and cornea

Question 40

how does aqueous humour drain | and in what condition can it get blocked

Answer 40

it drains through the iridocorneal angle (between iris and cornea) in the anterior chamber via trabecular meshwork into canal of Schlemm you get gluacoma

Question 41

what are the common causes of glaucoma

Answer 41

Trabecular meshwork deteriorates (age: chronic): open angle glaucoma Narrowing of iridocorneal angle (acute): closed angle glaucoma - is an anthropological emergency both cause a rise in intra-ocular pressure and damage to the optic nerve (optic disc cupping)

Question 42

what is open angle glaucoma what happens if it is left untreated how do you treat it

Answer 42

blockage within the trabecular mesh network leads to a rise in intraoccular pressure develops painlessly over time opticians screen for it cupping of optic disc and visual field loss if untreated can lead to damage of optic nerve causing impaired vision and blindness give topical beta blockers to reduce the production of aqueous humour and increase its drainage failing that a trabeculectomy may be required

Question 43

what is closed glaucoma how do they present what happens if untreated how do you treat it

Answer 43

narrowing of the irido-corneal angle (angle between cornea and iris) by the peripheral edge of the iris less common access to trabecular meshwork is blocked off rapid rise in intraoccular pressure present with sudden onset of a painful red eye, blurred vision or halos around objects (corneal odema) nausea and vomitting eye feels hard and tender to palpate through upper eyelid irreversible sight loss muscarinic eye drops (analgesia) drugs tor educes IOP

Question 44

how do we see

Answer 44

Light (photons) must reach the photosensitive retina to be detected by photoreceptors (rods/cones) – Action potentials generated in response to light – Pass via ganglion cells whose axons collect in area of optic disc- optic nerve • Light must reach and be focused on retina – Transparent medium – Refraction (bending of light) • Pathology affecting the retina, the transparency of structures anterior to retina or ability to refract light will cause visual disturbance

Question 45

why do we get refraction of light as light enters the eye

Answer 45

Light will be refracted as it passes through a number of structures and ‘fluids’ from outside eye towards retina – From air into liquid tear film-refract – Through cornea- refract (most refraction of light occurs at the air-cornea interface) – Through lens and vitreous humour before reaches retina

Question 46

what is the accommodation reflex

Answer 46

Light rays from near-objects are more divergent and require greater refraction to bring them into focus on retina the cornea alone cannot bend light enough so we need the lens to adjust • Eye can accommodate to do this – Pupil constricts – Eyes converge (image is brought to focus on same point of retina in both eyes) – Lens becomes more biconcave (fatter)- ciliary bodies contract and move in to release the tension Focusing Near Objects Requires Greater Refraction of Light

Question 47

what happens to your lens as you get older

Answer 47

As you get older the lens becomes stiffer The lens is less able to change shape Presbyopia- age related inability to focus near objects Have to hold things at arms length

Question 48

which cranial nerves supply the muscles that move the eyeball

Answer 48

CNIII CNIV CNVI occulomotor nerve innervaes most of them

Question 49

what is the control of the extrinsic (etraoccular) muscles of the eye e.g. muscles of the eyelid and muscles that move the eye ball (globe)

Answer 49

somatic motor nerves- conscious control | some sympathetic innervation too

Question 50

what is the control of the intrinsic muscles of the eye e.g. Muscles of the iris (dilator and constrictor of the pupil) and Ciliary muscle controls thickness of the

Answer 50

autonomic visceral nerves

Question 51

how many muscles move the eyeball what is their attachment where do they originate from

Answer 51

six sclera of eyeball most muscles originate from a fibrous ring at the back of the orbit (SR, IR, MR, LR)

Question 52

What are the two muscles not innervated by the occulomotor nerve

Answer 52

lateral rectus innervated by abducens | superior obliqe innervated by trochlear

Question 53

what muscles enables the eyes to look directly upwwards

Answer 53

Superior rectus pulls the eye up and pull the eyeball in slightly medially(inwards) Inferior oblique also helps to pull the eye up and slightly out The slightly medial action of the superior rectus is cancelled out by the slight lateral action of the inferior obliques so we can look directly up in the midline

Question 54

which muscles are moving the eyes downwards

Answer 54

Inferior rectus - depresses eyeball and brings it in slightly medially (inwards) Superior oblique also helps move the eye down, slightly moves the eye laterally (down and out) Intorts the eyeball- turns clockwise (when we rotate head) Secondary action of inferior rectus and superior oblique cancel out so we have a direct downward gaze so eye is directly in the midline

Question 55

what is the secondary action of superior oblique

Answer 55

roll the eye out and down | intort the eyeball- roll it clockwise

Question 56

what is the secondary action of inferior oblique

Answer 56

Roll the eye up and out | Extort the eyeball (roll it anticlockwise)

Question 57

what is the secondary action of superior and inferior rectus

Answer 57

roll the eye inwards medially

Question 58

what is the main action of superior oblique

Answer 58

depresses the eyeball

Question 59

what is the main action of inferior oblique

Answer 59

elevates the eyeball

Question 60

how do we test the lateral and medial rectus muscles

Answer 60

get the patient to look straight forwards and abduct and adduct the eye (look from side to side)

Question 61

how do we test the action of superior oblique

Answer 61

Move eye into medial position (looking towards nose) then move eyeball down

Question 62

how do we test the action of inferior rectus

Answer 62

Move eye into lateral position then move eyeball down

Question 63

how do we test the action of inferior oblique

Answer 63

Move eye into medial position then move eyeball up

Question 64

how do we test the action of superior rectus

Answer 64

Move eye into lateral position then move eyeball up

Question 65

what muscles is the main depressor of the eye when the eyeball is starting from the medial position

Answer 65

superior oblique

Question 66

why might you get a crainal nerve palsy

Answer 66

raised intracranial pressure (e.g. intracranial haemorrhage or tumour) But can also be affected by vascular disease (microvascular complications) from diabetes and hypertension

Question 67

how does the eye look if we get a CNIII palsy and why

Answer 67

the eye looks down and out this is because the only two extra occular muscles not innervated by thecocculomotor nerve are lateral rectus and superior oblique eye struggles to open as LPS is paralysed- complete ptosis dilated pupil as CNIII also carries parasympathetics to the sphincter pupillae muscle causing constriction

Question 68

how does the eye look if we get a CNIV palsy and why what do patients do to compensate

Answer 68

eyeball is held extorted- up and in trochlear nerve innervates the superior oblique muscle which acts to intort and move eyeball down and out they tilt their heads slightly report difficulty when looking down and medial- walking down stairs and reading

Question 69

how does the eye look if we get a CNVI palsy and why symptoms

Answer 69

``` eye inwards abducens nerves innervates lateral rectus so get unopposed pull of medial rectus unable to abduct eye on affected side diplopia made worose on horizontal gaze ```

Question 70

why might you get a CNIII palsy

Answer 70

vasculopathic tumour anneurysm

Question 71

why might you get a CNIV palsy

Answer 71

vasculopathic tumour congenital trauma

Question 72

why might you get a CNVI palsy

Answer 72

vasculopathic tumour cranial pressure