Anatomy: orbital cavity, eyelids, lacrimal apparatus, conjunctiva Flashcards
What shape is the orbital cavity?
Pyramidal
Apex points posteriorly and base anteriorly
What bones of the skull make the roof of the orbital cavity?
Frontal and lesser wing of sphenoid
What bones of the skull make up the floor of the orbit?
Maxilla, palatine and zygomatic
What bones make up the medial wall of the orbit?
Ethmoid, maxilla, lacrimal, sphenoid
What bones of the skull make up the lateral wall of the orbit?
Zygomatic, greater wing of sphenoid
What are the 3 openings at the apex of the orbit called?
Superior orbital fissure
Inferior orbital fissure
Optic canal
What paranasal air sinus is below the orbit?
Maxillary
What paranasal air sinus is medial to the orbit?
Ethmoid
Which parts of the orbital cavity are weakest?
Medial wall and floor (due to the air filled cavities)
What is another term for eyelids?
Palpebrae
What is the function of the eyelids?
Protect the eye when palpebral fissure closed
Keep cornea moist by covering it in a tear film
The inner surface of the eyelid is lined by what?
Palpebral conjunctiva - this reflects on the eyeball and is continuous with the bulbar conjunctiva (overlays the anterior surface of eye)
Movement of the eyelids occurs via what 2 muscles?
Obicularis occuli and levator palpebrae superioris
What is LPS innervated by?
Occulomotor nerve
What innervates obicularis occuli?
Facial nerve
What makes up the fibrous skeleton of the eyelids?
Tarsal plates
What glands do the tarsal plates contain?
Meibomian glands - modified sebaceous gland secreting lipid
What are the contents of the orbital cavity?
Lacrimal apparatus Nerves and blood vessels Orbital fat Globe of eye Extra ocular muscles
What is the orbital septum?
Thin sheet of fibrous tissue originating from orbital rim that separates intra orbital contents from eyelid fat and obicularis oculi
Why is the orbital septum useful?
Prevents infection spreading from pre septal space to post septal space
Meibomian glands open at the lid margin. Two other types of glands also open here, what are they called?
Glands of Moll
Glands of Zeiss
What type of glands are glands of Moll?
Modified sweat glands
What type of glands are glands of Zeiss?
Sebaceous glands
Obstruction to the tarsal glands can lead to a painless swelling of the eyelid called…
A chalazion
What is a stye?
An acute infection of a gland of Moll, Zeiss or the eyelash follicle
What is another name for a stye?
Hordeolum externum
What comprises the lacrimal apparatus?
Lacrimal glands, lacrimal ducts, lacrimal canaliculi
Where is the lacrimal gland located?
In a fossa on the upper lateral part of the orbit
Describe the route of the lacrimal fluid
From the lacrimal gland through the lacrimal ducts and into the conjunctival sac -> into lacrimal lake at medial angle of eye -> drains into lacrimal sac via lacrimal canaliculi then down the nasolacrimal duct
Where does the nasolacrimal duct open into?
Nasal cavity - inferior meatus
It is then swallowed
Is there any anastomotic pathways for the drainage of tears?
No - an obstruction will cause overflow
What is tear overflow called?
Epiphora
What is the conjunctiva and what does it cover?
A transparent mucous membrane that produces mucus and tears
Covers the white of the eye (sclera) and lines the inside of the eyelids (forming a conjunctival sac)
Does the conjunctiva cover the cornea?
No
Is the conjunctiva vascular ?
Yes
What is the role of blinking?
Washes tear film across front of eye - rinsing and lubricating conjunctiva and cornea
Why are tears needed?
Provide smooth surface
Allows light rays to be refracted uniformly
Lubrication to prevent friction
Antibacterial properties
What are the 3 components of the tear film?
Surface lipid layer - from Meibomian glands
Middle aqueous layer - from lacrimal gland
Inner mucus layer - from goblet cells of conjunctiva and epithelial cell surface
Tears are rich in protein especially…
IgA
