8.1.1 Functional Anatomy of Orbit and Eye Flashcards
What bones form the orbit?
Frontal bone
Ethmoid bone
Lacrimal bone
Maxilla
Zygomatic bone
Sphenoid bone
What bones form the walls of the orbit?
Base of pyramid (faces anteriorly)- tough orbital rim
Floor- Maxilla and zygomatic bone
Roof- Orbital plates of frontal bone and lesser wing of sphenoid
Medial- ethmoid,maxilla,lacrimal bones
Lateral- zygomatic bone and greater wing of sphenoid
What are the weakest parts of the orbit?
Floor and medial wall as the ethmoid and maxilla have air sinuses which makes the walls weaker
Label the image
What are the implications of the anatomical relations of the orbit?
Orbital surgery
Spread of infection, into or out from orbit e.g. acute sinusitis involving ethmoid sinus can spread into orbit
Orbital trauma
What occurs in an orbital blowout fracture?
Trauma to the front of the eye, eye is pushed backwards, this causes a sudden rise in intra-orbital pressure, causing a fracture of the floor of the orbit (maxilla)
What occurs after a fracture of the orbital floor?
- Orbital contents prolapse & bleeding into maxillary sinus
- Soft tissue and muscles near orbital floor can trap in fracture site
- Entrapment prevents upward gaze (may restrict other eye movements)
Why is eye movement affected in oribtal blowouts?
Extraocular muscles attach to the underneath of the eye, they become trapped and unable to work properly
Patient unable to look up and normal gaze is affected
Why might you get numbness over the cheek, lower eyelid and upper lip in orbital blowout fractures?
Maxillary branch of trigeminal can be affected
(Infraorbital branch)
How do you manage an OBF?
- CT orbit and referral to opthalmology
- Prophylactic antibiotics
- Avoid blowing nose and driving until double vision resolves
- 1 week follow up, entrapment, diplopia and enophthalmos may resolve as oedema decreases
- May need surgical repair if symptoms persist 1-2 weeks post injury
Label the image
What nerve is responsible for carrying sensation to the eye?
Opthalmic division of trigemnial Va
What is the main arterial supply to the orbit and eye?
Opthalmic artery (1st branch of ICA)
Central retinal artery (supplies retina)
What is the main venous drainage of the orbit and eye?
Opthalmic veins (superior and inferior)
connections with cavernous sinus, pterygoid plexus and facial vein
Where does the central retinal artery and vein run?
Runs within the dural sheath of the optic nerve
What are the blood supplies to the retina?
Central retinal artery
Choroid layer (fed by anterior and posterior ciliary arteries) - choriocapillaries
Retina needs both circulations to function properly
What is the function of the eyelid?
Protects the front of the eye
What does the eyelid consist of?
Skin
Subcutaneous tissue
Muscles
Tarsal plate
What are the key muscles within the eye lid?
Orbicularis oculi (palpebral part) - closes eye lid CNVII
Levator palpabrae superiosis- retracts eye lid, skeletal muscle portion CNIII, smooth muscle portion supplied by sympathetics
What additional muscles are also present in the orbit?
Mullers muscle (Superior Tarsal)
Frontalis
What are the main two glands in the eyelid?
Meiboman glands- within tarsal plate (modified sebaceous glands)
Sebaceous glands- associated with lash follicle
What do meibomian glands secrete?
Lipid layer of tear film to prevent tear evaporation and spillage over lid
What do glands associated with lash foillicle secrete?
Sebaceous- oily substance
What happens when glands in the eyelid are blocked?
Can cause a lump within the eyelid
What is the difference between a meibomian cyst and a stye?
Stye
* Outer part of the lid
* Painful
* Red with a white punctum (head)
* Infective cause (staphylococcus)
* Treat with warm compresses, may need ABX
Meibomian cyst
* Deeper in the lid
* Painless
* Firm lump, palpable, enlarges gradually
* Non-infective cause, blocked duct
* 1/3 resolve spontaneously
* May need surgical incision if it persists
What glands are blocked in a stye?
Glands of Zeis
What is blepharitis?
Inflammation of the eyelid margin (base of the eyelashses)
What causes blepharitis?
Multifactoral causes:
Staphylococcus, meibomian gland dysfunction etc…
What are some symptoms of blepharitis and how do we manage it?
Crusting, dry eye lids, may be swollen and red
Not serious, treat with warm compress and good lid hygiene
What is the orbital septum?
Thin fibrous sheet originating from orbital rim, continuous with the tarsal plate
What does the orbital septum do?
Separates intra-orbital contents from muscles and subcutaneous tissue of eyelid
Barrier against infection spreading from superficial eye lid region (pre-septal) into orbital cavity proper (post-septal)
What is pre-septal (periorbital) cellulitis?
Infection involving superficial tissues, the eyelid (anterior to septum)
Eye movements and vision unaffected, painful
What is post-septal cellulitis?
Infection involving tissues within the orbit
What causes periorbital cellulitis or pre-septal cellulitis?
Superficial infections e.g. bites or wounds
Confined to tissues superficial to orbital septum and tarsal plates
What causes post-septal cellulitis?
Spread of infection from paranasal air sinuses
What are some signs and symptoms of post-septal cellulitis?
Proptosis/exopthalmous
Reduced +/- painful eye movements
Reduced visual acuity
Asides from visual effects why is post-septal cellulitis particularly worrying?
Orbital veins drain to cavernous sinus
Potential route for infection to spread intracranially, cavernous sinus thrombosis and meningitis
Optic nerve damage
