Anatomy of the Orbit Flashcards
How many bones make up the orbit?
7
Name the seven bones which make up the orbit.
Frontal
Zygomatic
Lacrimal
Maxillary
Sphenoid
Ethmoid
Palatine
There are three foramina which allow neurovascular structures to enter the orbit. Name them.
Optic foramen
Superior orbital fissure
Inferior orbital fissure
The walls of the orbits are weak, especially the medial and inferior walls. Why is this?
Surrounded or adjacent to paranasal air sinuses
Which paranasal air sinus is just above the orbit?
Frontal air sinus
Which paranasal air sinus is just medial to the medial wall of the orbit?
Ethmoid air sinus
Which paranasal air sinus is just inferior to the floor of the orbit?
Maxillary air sinus
The eyeball is a lot smaller than the space of the orbit. What fills out the rest of the orbit?
Fat
What is the length of eyeball compared to the length of orbit?
Eyeball- 24mm
Orbit- 40mm
What does the fat in the orbit do?
Cushions the eyeball
If you see someone with sunken eyeballs, what can this tell us?
They are late in the process of starvation as the fat supplies of the orbit are some of the last stores to be used.
Compare the inside and outside of an eyelid.
Outside- skin
Inside- mucous membrane (conjunctiva)
What does the tarsal plate (solid plate) of the eyelid do?
Keeps shape of eyelid
What is the tarsal plate of the eyelid made of?
Dense connective tissue
What is found within the tarsal plate?
Meibomian glands
What is the function of meibomian glands?
Secretes oily substance which lines the tear film and prevents tears from evaporating
Which muscles opens and closes the eyes?
Orbicularis oculi
What happens if the Meibomian sebaceous glands are blocked?
Oily secretion is trapped inside and causes painful swelling
What happens to the conjunctiva after it lines the inner side of the eyelid?
Turns on itself at a point called the fornix.
Therefore, there is a superior and inferior fornix, a fold in which the conjunctiva turns and covers part of the sclera.
Why is the conjunctiva pink?
Many capillaries
What does the conjunctiva not cover?
The cornea as needs the light
What does the sclera have over it and how can you tell?
Conjunctiva- transparent but can see tiny blood vessels
Which gland forms tears?
Lacrimal gland
What is the parasympathetic innervation for the lacrimal duct?
Facial nerve (CN VII)
What do the tears formed in the lacrimal gland coat?
Outer surface of sclera, conjunctiva and cornea.
This is known as a tear film.
What helps to spread the tear film around the anterior aspect of the eyeball?
Blinking
What do tears drain through?
Punctae sitting at the medial side of each eyelid and then drains into the lacrimal sac.
The lacrimal sac sits over the lacrimal bone. After the tears have drained into the lacrimal sac after the punctae, where do they drain to?
Through nasolacrimal duct into the inferior meatus.
Just go over the pathway of tears.
From lacrimal gland -> coat eye -> drain into punctuae -> drain into lacrimal sac -> drain into nasolacrimal duct ->drain into inferior meatus
What role does the orbicularis oculi have in tear production?
Squeezes lacrimal sac to release tears
There are intrinsic and extrinsic ocular muscles. What do the intrinsic muscles help to control?
Control pupil diameter.
Move the eye to look in different directions
Which muscles in the iris help to constrict the pupil?
Sphincter pupillae (constrictor pupillae).
Which muscles in the iris help to dilate the pupil?
Dilator puplillae
What type of innervation causes pupils to dilate?
Sympathetic innervation
Therefore, which type of innervation supplies the dilator pupillae?
Sympathetic innervation
Which type of innervation will supply the constrictor pupillae and ultimately cause the pupil to contrict?
Parasympathetic inneration
Which nerve carries parasympathetic innervation to the constrictor pupillae?
Oculomotor nerve (CN III)
Name the three intrinsic muscles.
Constrictor/sphincter pupillae
Dilator pupillae
Cililiaris muscle
What is the specific role of the ciliaris muscle?
Helps to alter lens to focus on closer objects.
Which type of innervation supplies the ciliaris muscle?
Parasympathetic innervation
-> both muscles beginning with C get parasympathetic innervation
Which nerve supplies the parasympathetic innervation the the muscles of the eye?
CN III- oculomotor nerve
What do extrinsic muscles do?
Muscles originate from the bony orbit and attach to the eyeball t help to move it.
There are four straight extrinsic muscles called recti. Name them.
Medial rectus
Lateral rectus
Superior rectus
Inferior rectus
There are two oblique extrinsic muscles. Name them.
Superior oblique
Inferior oblique
Where do the recti muscles arise from?
Apex of the orbit from the annular fibrous ring.
Which extrinsic oblique muscles enters the eye anteriorly?
Inferior oblique muscle
Which extrinsic oblique muscles enters the eye posteriorly?
Superior oblique muscle
There is another muscle which comes from the back of the orbit but attaches to the upper eyelid. What is it called?
Levator palpebrae superioris muscle
What is the origin and insertion of the Levator palpebrae superioris?
Origin- roof of orbit
Insertion- upper eyelid
What is the origin and insertion of the rector muscles?
Origin- tendinous ring
Insertion- sclera anteriorly
What is the origin and insertion of the superior oblique muscle?
Origin- lesser wing of sphenoid
Insertion- sclera posteriorly
What is the origin and insertion of the inferior oblique muscle?
Origin- medial part of orbit floor
Insertion- sclera posteriorly
Which nerve supplies the superior oblique muscle?
Trochlear nerve (CN IV)
Which nerve supplies the lateral rectus muscle?
Abducent nerve (CN VI)
Which nerve supplies all the muscles of the eye except for the superior oblique and lateral rectus?
Oculomotor nerve (CN III)
How many cranial nerves enter the orbit?
4
Name the cranial nerves which enter the orbit.
Trochlear nerve (CN IV)
Oculomotor nerve (CN III)
Optic nerve (CN II)
Abducent nerve (CN VI)
