Session 9: Functional Anatomy of the Orbit and Eye Flashcards
Main arterial supply of the eye and its orbit.
Ophthalmic artery and subsequent branches (retinal arteries)
Main venous drainage of the eye and its orbit.
Ophthalmic veins (superior and inferior),
What do the ophthalmic veins drain venous blood into?
Cavernous sinus
Pterygoid plexus
Facial vein
General sensory from the eye (including conjunctive and cornea).
Ophthalmic branch of the trigeminal nerve (CN Va)
Special sensory vision from retina.
Optic nerve
Motor nerves to muscles of the eye and orbit.
CN III
CN IV
CN VI
What parts of the orbit are the weakest and most susceptible to damage?
The inferior part (floor) which mainly comprise of the maxilla and the medial walls which mainly comprise of the ethmoid bone.
What is thinner; the medial wall or the floor?
The medial wall, even if the medial wall is thinner the floor is more susceptible to damage.
How come even if the medial wall is thinner (lamina papyracea) the floor is still more susceptible to damage?
Because the ethmoidal sinuses (air cells) act as buttresses and convey an added strength to the medial wall.
Give examples of injuries that is common to cause a fracture of the floor or medial wall of the orbit.
Direct impact to the front of the eye, e.g. by a fist or a ball.
This leads to a sudden increase in infraorbital pressure.
What is a fracture called that involves the floor of the orbit?
An orbital blow-out fracture.
More than making the orbit susceptible to trauma, what other complications might ensue due to the thin medial and inferior walls?
In acute sinusitis of the ethmoidal air cells the infection can break through the medial wall and cause orbital cellulitis.
Explain Orbital blow out fractures.
Sudden increase in intra-orbital pressure leads to fractures of the floor of the orbit (maxilla)
What happens in the event of a orbital blow out fracture to the orbital contents?
The orbital contents can prolapse and bleed into the maxillary sinus.
The fracture site can also trap structures like extra ocular muscles that are located near the orbital floor.
What will trapping of an extra ocular muscle cause?
Prevents an upward gaze on the affected side.
Common clinical presentation of an orbital blow out fracture.
Periorbital swelling
Pain
Double vision (diplopia) that worsens on a vertical gaze.
Numbness over cheek, lower eyelid and upper lip as well as upper teeth and gums on affected side.
Why might you get numbness over cheek etc… in an orbital blow out fracture?
Can cause damage to the infraorbital nerve as it runs through the infraorbital fracture.
What protects the front of the eye?
Skin, subcutaneous tissue, tarsal plate and muscles.
The orbicularis oculi (palpabral part) as well as the levator palpebrae helps close and open the eyelids respectively.
Glands like meobomian glands and sebaceous.
Function of the tarsal plates.
Eyelids are strengthened and given their shape by tarsal plates.
Functions of the meibomian glands.
Oily secretions from the glands lubricate the edge of the eyelids.
This secretion mix with the tear film and prevents the tears from evaporating too quickly.
What else adds secretion to the tear film?
The lacrimal apparatus.
What does the lacrimal apparatus consist of?
The lacrimal gland, the lacrimal ducts and the lacrimal canaliculi.
Where can the lacrimal glands be found?
In a fossa called the lacrimal fossa on the superolateral part of the orbit.
Explain the route of the lacrimal fluid.
Secreted by the lacrimal gland. Enters the conjunctival duct through the lacrimal ducts and into the lacrimal lake.
The fluid drains into the lacrimal sac and then into the nasal cavity via the nasolacrimal duct.
Explain the function of blinking in protecting the eye.
The eye blinks when the cornea becomes dry. This leads to a film of fluid covering the cornea.
This also sweeps any dust and other foreign material to the medial angle of the eye.
What is a stye?
Infected hair follicle or sebaceous gland. This can be blocked.
Usually a staphylococcus infection.
What is a meibomian cyst?
Blockage of the meibomian glands leading to a cyst.
Meibomian cysts are found deeper than styes.
What is blepharitis?
Inflammation of the eye lid.
This includes the skin, the lashes and the meibomian glands.
What is the orbital septum?
A thin sheet of fibrous tissue that originates from the orbital rim periosteum and then blends with the tarsal plates.
Function of the orbital septum.
Along with the tarsal plates they separate the subcutaneous tissue of the eyelid and orbicularis oculi muscle from the intra-orbital contents.
It acts as a barrier against superficial infection spreading from pre-septal to post-septal space.
What is periorbital cellulitis?
Also called pre-septal cellulitis.
An infection occurring within the eyelid tissue and superficial to the orbital septum.
Usual cause of periorbital cellulitis.
Secondary to superficial infections like from bites and wounds. Can also be secondary to bacterial sinusitis in children.
Clinical presentation of periorbital cellulitis.
Red around the eye
Pain
Swelling
Ocular functions like eye movements and vision remains unaffected.
It can be difficult to differentiate between peri-orbital cellulitis and more severe orbital ones.
What is orbital cellulitis?
Also called post-septal cellulitis.
This is an infection within the orbit posterior or deep to the orbital septum.
Clinical presentation of orbital cellulitis.
Proptosis/exopthalmous
Reduced and painful eye movement.
Reduced visiual acuity.
Complications of orbital cellulitis.
If not treated early it can lead to visual impairness.
Also as the orbital veins drain to the cavernous sinus, pterygoid venous plexus and the facial veins the infection can spread intracranially and lead to cavernous sinus thrombosis or meningitis.
What is epiphora?
Obstruction of the drainage of lacrimal tears.
This is overflow of tears over lower eyelid
Three layers of the eyeball.
Outer
Middle
inner
What does the outer layer contain?
Sclera and the transparent cornea which is a continuation of the sclera anteriorly.
What does the middle layer contain?
Choroid
Ciliary body
Iris
This layer is highly vascular
What does the inner layer contain?
The retina
Contains inner photosensitive layer and a outer pigmented layer.
What is the eyeball’s position maintained by?
Suspensory ligament
Extra-ocular muscles
Orbital fat ++