Orbit And Eye

Question 1

Descirb the anatomy of the orbit

Answer 1

Ss, spr

Question 2

Which bones make up the orbit

Answer 2

Sup

Question 3

What is the main arterial supply to the orbit

Answer 3

• Main arterial supply is ophthalmic artery and its
branches
Central retina artery pierces the (smh) nerve?

Question 4

Descirb the Opthalmic veins

Answer 4

Ophthalmic veins (superior and inferior) drain
venous blood into cavernous sinus, pterygoid plexus
and facial vein
Sup orb fiss ->
Inf -> pterygoid venous plexus

Question 5

What are the anatomical relation of the orbit

Answer 5

• Important anatomical relations include
– Paranasal air sinuses (maxillary and ethmoid) - sinusitis can move into orbit, particularly ethmoid, due to thin walls.
– Nasal cavity
– Anterior cranial fossa
• Implications for
Coronal Section
• Orbital trauma
• Spread of infection
Medial wall and floor of the orbit are the weakest parts of the orbital cavity

Question 6

What is an orbital blow out fracture

Answer 6

Sudden increase in intra-orbital pressure (e.g. from retropulsion of eye ball [globe] by fist or ball) fractures floor of orbit [maxilla]
• Orbital contents can prolapse and
bleed into maxillary sinus,
• Fracture site can ‘trap’ structures
e.g. soft tissue, extra ocular muscle
located near orbital floor
• Prevents upward gaze on the
affected side- Orbital contents tethered from below

Question 7

Describe and explain teh clinical presentation of orbital blowout fractures

Answer 7

• History of trauma to the eye/orbit
• Periorbital swelling, painful
• Double vision (worse on vertical
Looking straight ahead gaze)
• Double vision
• Anaesthesia over affected cheek (upper teeth and gums) on affected side
Eye appears sunken because floor of orbit has given way, contents have shifted down. When asked to oo up, affected eye struggles because orbital contents are tethered
Losss of feeling over cheek, upper teeth and gums, - infraorbital nerve which is one of the branches of Vb, runs though floor of orbit though infraorbial foramen - innervates skin of lower eyelid, cheek upper teeth, gums

Question 8

Describe teh structure of the eyelid

Answer 8

• Consist of skin, subcutaneous tissue, tarsal plate, muscles
– Orbicularis oculi (Palpebral part)
– Levator palpebrae superioris
Tarsal plate is a connective tissue stature which gives structure to the eyelid

• And glands
– Meibomian glands - Glands within the tarsal plate secrete an oily (lipid-rich) substance onto edges of lid; help prevent evaporation of tear film and tear spillage: can block causing a Meibomian cyst
Eyelash follicles can also block (infection-staph) causing styes

– Sebaceous glands associated
with lash follicle
Sebaceous glands help nourish the hair folllicle
Glands secrete on lid margin - substances form part of tear film

Question 9

Whar are diseases of the glands of the eyelid and the eyelid

Answer 9

Glands within the tarsal plate secrete an oily (lipid-rich) substance onto edges of lid; help prevent evaporation of tear film and tear spillage: can block causing a Meibomian cyst - not infected - glands becomeblocked and there is some inflammation.swelling is a little bit deeper inside the eyelid. Not particularly painful
Eyelash follicles can also block (infection-staph) causing styes - painful, white head visible in the area of swelling, on the tip of the eyelid

Question 10

What is the orbital septum

Answer 10

Thin sheet of fibrous tissue originating from orbital rim periosteum blends with tarsal plates
• Orbital septum & tarsal plates separate subcutaneous tissue
of eyelid and orbicularis oculi muscle from intra-orbital
contents
• Acts as a barrier against superficial infection spreading from
the pre-septal to post-septal space (orbital cavity proper)
Blends with tarsal plates and tendon of lps

Question 11

What is periorbital (pre-septal) cellulitis

Answer 11

Difficultto tell the difference between peri orbital or orbital - need to refer to specialist - peri - oral antibiotics, orbital need surgical drainage and antibiotics?
• Secondary to superficial infections e.g. from bites, wounds,
– May be secondary to bacterial sinusitis (fronto-ethmoidal sinuses) in children
• Confined to tissues superficial to orbital septum (and tarsal plates)
• Ocular function (eye movements/vision) remains unaffected
• Can be difficult to differentiate between peri-orbital and the more severe orbital cellulitis
• If any doubt, urgently refer (high dose IV antibiotics + surgical drainage)
Infection in front of septum - subcutaneous tissues of eyelid - t is very red or swollen - may be sendary to bite or break in thhe skin. Confined in front of septum and plates. Does not affect structures to do with ocular function. Eye movements and vision is normal.

Question 12

What is orbital cellulitis

Answer 12

Infection WITHIN the orbit* posterior or deep to the orbital septum
*involving orbital tissue/fat and extraocular muscles not the globe of the eye itself
Orbital veins drain to cav sinus -> pterygoid v plexus -> facicalveins - potental route for infection to spread - > cav sinus thrombosis, meningitis, SSSSS

Question 13

What are the contents of the orbital xvaoty

Answer 13

• Eyeball • Fat • Associated extra-ocular muscles • Nerves and blood vessels • Lacrimal apparatus

Question 14

What is the lacrimal apparatus

Answer 14

Structures involved in tear film production and drainage
• Lacrimal gland (tear production), lacrimal sac and ducts (tear drainage)
– Ducts = canaliculi and nasolacrimal duct
• Blinking (orbicularis oculi-palpebral part) washes tear film across front of eye, rinsing and lubricating conjunctivae and cornea
• Tears are ultimately drained into nasal cavity
• Obstruction to the drainage system leads to epiphora (overflow of tears over lower eyelid)
Spr

Question 15

Describe teh anatomy of the eyeball

Answer 15

• Eyeball has three layers
• Outer: sclera (white of eye) continuous
anteriorly as transparent cornea- Choroid, becomes ciliary body, becomes iris - all the choroid layer
• Middle: choroid, ciliary body and iris (vascular) - Choroid, becomes ciliary body, becomes iris - all the choroid layer
• Inner: retina (inner photosensitive layer lying on an outer pigmented layer)
• Eyeball is maintained in position by
• Suspensory ligament (sits underneath like a sling)
• Extra-ocular muscles
• Orbital fat ++ Lots of fat to hold eye off the floor of the orbit

Question 16

What is teh conjunctiva

Answer 16

• Conjunctiva is a transparent mucous membrane
– Produces mucous and tears
• Covers white of eye (sclera) and lines inside of eyelids (forming a conjunctival sac); does not cover over cornea
– Limbus (junction of conjunctivae with cornea)
• Highly vascular with small blood vessels within the membrane A
• Inflammed and injected in infections e.g. conjunctivitis - Conjunctivitis - infection - itchy, engorgement of blood vessels
• Haemorrhage from blood vessels readily visible as a subconjunctival haemorrhage - not to worry

Question 17

Descrbe how light is focused

Answer 17

• Need transparent structures and medium

• Need to refract light* (bending of light) to
bring to a focal point - macula

• Several structures refract light (all transparent)
• Cornea and its associated tear film - very important
• Lens
• Aqueous humour and vitreous humour
• Shape of your eyeball also effects ability to focus light appropriately onto retina
• Myopia (short-sighted) - eyeball too long
• Hypermetropia (long-sighted)

Question 18

What are rods and cones

Answer 18

• Rods (active at low light levels, do not
mediate colour vision)
• Abundant in peripheral parts of retina • Cones (high definition, colour vision- active
at high light levels) • Concentrated within the macula of the retina • Fovea = only cones

Question 19

How are apps interpreted

Answer 19

Photoreceptors - photosensitive part of the yes - rods and cones
• Action potentials generated in response to
light pass via retinal ganglion cells (RGC)

• RGC axons collect in area of optic disc forming the optic nerve
– Optic disc = blind spot as no
photoreceptors present here

• Action potentials propagated along visual pathway to occipital lobe for interpretation

Question 20

What is the accommodation reflex

Answer 20

Focusing Near Objects Requires Greater Refraction of Light
F• Light rays from near-objects are more divergent
• Greater refraction, beyond capabilities of cornea (which is fixed in shape) to bring into focus on retina
• Eye accommodates
– Pupil constricts (limits amount of light coming through)
– Eyes converge (to ensure image remains focused on same point of retina in both eyes)
– Lens becomes more biconvex (fatter) by contraction of ciliary muscle
• Note, as we age the lens becomes stiffer and less able to change shape
– Presbyopia (age-related inability to focus near-object)

Question 21

What can cause blurring of vision

Answer 21

Pathology affecting
• transparency of structures anterior to retina
- e.g. opacity in lens such as cataract,
• ability of structures to refract light
- e.g. irregularity of corneal surface
(astigmatism), ability of lens to change shape (presbyopia), or shape of eyeball
• and the retina (including macula) or optic nerve
• E.g. retinal detachment, age-related macular
degeneration, optic neuritis
• will cause blurring of vision/ decreased acuity

Question 22

What are the fluids which help maintain the shape o the eyball

Answer 22

Aqueous humour filling anterior and posterior chambers

Vitrous humour within vitreous chamber

Question 23

Scribe the production and drainage of aqueous humorist

Answer 23

• Aqueous humour secreted by ciliary
processes within ciliary body
• Flows from posterior chamber, through pupil into anterior chamber
• Nourishes lens and cornea
• Drains through iridocorneal angle (between iris and cornea)
• Via trabecular meshwork into canal of
Schlemm (circumferential venous channeldraining into venous circulation)

Question 24

What si glaucoma

Answer 24

Optic nerve Damage Secondary to Raised Intraocular Pressure
• Drainage of aqueous humour from anterior chamber blocked causing rise in intra-ocular pressure
– Can develop chronically or acutely
• Chronic=open-angle glaucoma [most common]
– Trabecular meshwork deteriorates as we age
– Many asymptomatic [picked up on routine eye tests]
– Increased IOP -> ↑ optic disc cupping
– Gradual loss of peripheral vision
• Acute-=closed-angle glaucoma [less common]
– Narrowing of iridocorneal angle
– Ophthalmological emergency
• Sight-threatening - Something has caused the pressure to increase. This needs attention much sooner. Iris plushies forward and narrows he angle. Obstructing the outflow so pressure rises very quickly - immediate detrimental effect - damagopting nerve - sight loss

Question 25

Describe the presentation fo acute angle closure glaucoma

Answer 25

* Older patient 55 years + (most common 70s-80s) * Acutely painful red eye ++ * Irregular oval-shaped pupil (fixed) * Blurring of vision * Halo’s around lights (due to corneal oedema) * Nausea and vomiting * Medical (drugs to reduce IOP) then surgical treatment

Question 26

Which are the muscles that move the eyeball

Answer 26

• Six muscles move the eyeball and have attachment to the sclera – Superior, inferior, medial and lateral rectus – Superior and inferior oblique • Four muscles (the recti) arise from a common tendinous ring at the apex of the orbit • Nerve innervation can be remembered by LR6 SO4

Question 27

What happens at resting gaze

Answer 27

Primary Resting Gaze (position of rest) Equal and opposite pull of all extra ocular muscles • Constancy of activity in all extra ocular muscles on the eyeball, even at rest • Each muscle has antagonist of its movement but during resting gaze their actions are balanced allowing for forward gaze

Question 28

What happens when oen extra oxxular muscles contract

Answer 28

• Moving eye position involves exerting greater pull through action of certain extraocular muscles, while its antagonist relaxes • Muscles moving both eyes must be highly co-ordinated and move simultaneously - Communication at level of brain stem that les other eye know hitch way moving – Malalignment causes diplopia

Question 29

What are the actions of SR

Answer 29

``` Superior rectus (SR) will IR – Elevate – Slightly intorts (internally rotates) – Slight adducts (pull eye medially) ```

Question 30

What are the cations of inferior rectus

Answer 30

- depress - slightly extort - slightly adduct

Question 31

What are teh actions of superior and inferior obliges

Answer 31

• Superior* and inferior oblique (IO) approach eyeball from anteromedial corner of orbit IO – *consider the functional pull of SO being from the area of its trochlea • Superior oblique will – Intort (internally rotate) – Depress – Slightly abducts(pull eye laterally) SO ``` • Inferior oblique will – Extort (externally rotate) – Elevate IO – Slightly abduct (pulls eye laterally) ```

Question 32

What happens if one muscle is weaknened

Answer 32

* If a muscle is weakened, its ‘influence’/pull on the eyeball is lost- other muscle actions no longer antagonised (“balanced”) * Resting position of eyeball changes = strabismus (squint) * Can be congenital or acquired e.g. cranial nerve lesions

Question 33

Describe he clinical examination of eye movement

Answer 33

Need to Isolate Each Muscle to Test Them .. Clinical Examination of Eye Movements • Lateral and medial rectus – Straight forward as each only performs one action on the eye – Abduction and adduction of the eye Why the ‘H’? • elevation and depression (in midline) involves two muscles each • Move starting position of eye – Medially (adducting) first or laterally (abducting) first – before elevating and depressing • Changing starting position (abducted vs adducted) changes line of pull for superior/inferior recti and oblique muscles – Dominant actions on eyeball therefore change • Move the direction of gaze in line with pull of the muscle then elevate and depress

Question 34

What are the stations poistion to test each muscle

Answer 34

Lateral placed elevation - sup and inf rectus | Medial placed elevation - obliques

Question 35

What can affect the cranial nerves that innervate the axtraccular muscles

Answer 35

• Abnormalities of eye movements and diplopia (double vision due to malalignment of the eyes) – May be obvious from initial inspection of the eye – And/or become more apparent on testing eye movements • Cranial nerves III, IV, VI innervate muscles that move the eyeball • The cranial nerves can be affected by raised intracranial pressure (e.g. intracranial haemorrhage or tumour) – CN VI most commonly affected of the three in this context • But all can also be affected by vascular disease (microvascular complications) from diabetes and hypertension

Question 36

Describe cn iii palsies

Answer 36

• Most extra-ocular eye muscles innervated by CN III (except LR and SO) Dow and out bc lr and so onopposed • Innervates majority of muscle of eyelid (LPS) • Carries parasympathetic function to the sphincter pupillae muscle causing constriction – Run on outside of nerve • Compressive lesions (raised ICP tumour, aneurysm – Pupil involved • Vasculopathic (microvascular) lesions (e.g. diabetes/hypertension) – Pupil spared Bc tends to involved blood vessels supplying deeper parts of the nerve. Parasympathetics aren’t involved as early.

Question 37

Describe cn ivpalsies

Answer 37

• Innervates superior oblique muscle only • Superior oblique muscle acts to INTORT, and depress and abduct eye • Lose these actions so eyeball is held EXTORTED, slightly elevated and adducted • Compensate for the slight extortion of eyeball by tilting the head slightly (not seen in image) • Abnormality in gaze can be very subtle and often missed • Worsening diplopia (on downward vertical gaze) especially looking down and medially e.g. walking down stairs, reading – Remember SO is main depressor of the eyeball when in adduction

Question 38

Descrbe cn vi palsies

Answer 38

``` • Innervates lateral rectus • Unopposed pull of medial rectus muscle • Unable to abduct the eye on affected side • Report diplopia, made worse on horizontal gaze ```

Question 39

What s the mostly likely cause for cn iii iv vi lesions

Answer 39

• Most likely cause for CN III, IV and VI lesions is vasculopathic – Patients will be otherwise asymptomatic (apart from signs/symptoms directly relating to CN lesion) – Lesions usually self-resolve within few months) • History will help give a clearer indication for more concerning underlying cause – Headache (+/-) vomiting could suggest raised ICP (secondary to tumour or haemorrhage) – Recent head injury – Presence of pupil involvement in CN III lesions is of immediate concern