Orbit and the eye Flashcards
Which bones make up the orbit ?
- frontal bone
- zygomatic bone
- maxilla
- nasal bone
- sphenoid bone
- ethmoid bone
- lacrimal bone
What is the function of the eyelids ?
- protect the eyes
- eyelashes prevent dust and particles from entering the eyes
What are the different components of the eyelids ?
- outer skin
- inner conjunctiva (inner mucous membrane)
- eyelashes
- glands
Summarise the structure and function of the tarsal plates
- made of dense connective tissue
- they maintain the shape of the eyelids
- contain tarsal glands which secrete an oily substance
- each eyelid contains 1 tarsal plate so there are 4 tarsal plates in total
What is the function of the oily substance secreted by the tarsal glands ?
- lubricates the eyelid so they don’t stick together
- prevents the quick evaporation of tears
What are the muscles found in the eyelid ?
- orbicularis oculi
- superior tarsal muscles
- levator palpebrae superioris
Describe the function and innervation of the muscles found in the eyelid
- orbicularis oculi is a muscle of facial expression and it is supplied by the facial nerve
- levator palpebrae superioris is a skeletal muscle supplied by the oculomotor nerve
- superior tarsal muscle is a smooth muscle supplied by the sympathetic nervous system
- both of these muscles elevate the eyelid
What are the 2 parts of the orbicularis oculi muscle and where are they found ?
- orbital part : surrounds the orbital margin
- palpebral part : found within the eyelid
What is the orbital septum ?
It is a fibrous membrane which extends outwards to cover the gap in the orbit
How are the tarsal plates connected to the orbital margin ?
- connected to the medial margin of the orbit by the medial palpebral ligament
- connected to the lateral margin of the orbit by the lateral palpebral ligament
Where are the tarsal plates found in relation to the muscle ?
they are found deep to the palpebral part of the orbicularis oculi muscle
What is the function of the lacrimal apparatus ?
involved in the production, movement and drainage of tears
Describe the pathway of the tears
1) tears are produced in the lacrimal gland
2) they travel through lacrimal gland ducts across the cornea
3) they enter the lacrimal puncta which are openings in the eyelids
4) they then travel through the lacrimal canaliculi which are tubes
5) enter the lacrimal sac
6) through the nasolacrimal duct
7) into the inferior meatus of the lateral wall of the nasal cavity
Where is the lacrimal gland located ?
it is located superior and laterally in the orbit
What is the sensory innervation of the lacrimal gland ?
innervated by the lacrimal nerve which is a branch of the ophthalmic division of the trigeminal nerve
What is the secretomotor (parasympathetic) innervation of the lacrimal gland ?
it is very complex so look at lecture
What is the sympathetic innervation of the lacrimal gland ?
the sympathetic innervation of the lacrimal gland is from fibres of the superior cervical ganglion but it is only involved in vasoconstriction of blood vessels in the area
What does the lacrimal nerve supply ?
- sensory innervation to the lacrimal gland
- sensory innervation to the skin and fascia of of the lateral aspect of the upper eyelid
What does the external nasal nerve supply ?
- supplies skin on the dorsum and lateral aspect of the nose
What are the extrinsic muscles of the eye ?
- lateral rectus
- medial rectus
- inferior rectus
- superior rectus
- inferior oblique
- superior oblique
What is the general functions of the extrinsic (extraocular) muscles of the eye ?
they move the eyeballs
What is the trochlea ?
It is a cartilaginous component which contains the tendon of the superior oblique muscle
What is the position of the superior oblique muscle in relation to the medial rectus muscle ?
The superior oblique muscle lies superior to the medial rectus
Describe the action of the lateral rectus muscle
abduction - lateral movement of eyeball
Describe the action of the medial rectus muscle
adduction - medial movement of the eyeball
Describe the action of the superior rectus muscle
elevation - upwards and inwards movement of eyeball
Describe the action of the inferior rectus muscle
depression - downwards and inwards movement of eyeball
Describe the action of the superior oblique muscle
depression - downwards and outwards movement of eyeball
Describe the action of the inferior oblique muscle
elevation - upwards and outwards movement of eyeball
Describe the innervation of the extraocular muscles of the eye
- lateral rectus = abducent nerve
- superior oblique = trochlear nerve
- superior rectus, medial rectus, inferior rectus and inferior oblique = oculomotor nerve
What are the intrinsic eye muscles ?
- sphincter pupillae
- dilator pupillae
- ciliary muscles
Where are the intrinsic muscles of the eye found ?
in the eyelid
What is the function and innervation of the sphincter pupillae muscle ?
- when it contracts it will constrict the pupil
- innervated by the parasympathetic component of the oculomotor nerve
What is the function and innervation of the dilator pupillae muscle ?
- when it contracts it will dilate the pupil
- innervated by the sympathetic component of the oculomotor nerve
What is the function and innervation of the ciliary muscles ?
- they form a circular ring which surrounds the lens
- the lens is suspended to the muscles by suspensory ligaments
- innervated by the parasympathetic component of the oculomotor nerve
Describe what happens when there is no nerve stimulation to the ciliary muscles
- ciliary muscles will relax
- the circular ring will get bigger
- the ligaments become tense
- lens becomes thinner
- eye will focus on a distant object
Describe what happens when the ciliary muscles have parasympathetic stimulation
- ciliary muscles will contract
- the circular ring will get smaller
- the ligaments become relaxed
- lens becomes thicker
- eye will focus on a near object
- this process is known as accommodation
Describe the ciliary ganglion
- it is a collection of neuronal bodies found between the optic nerve and lateral rectus muscle
- it contains the preganglionic parasympathetic fibres of the oculomotor nerve and the postganglionic parasympathetic fibres of the short ciliary nerves
What is the function of the short ciliary nerves ?
they innervate the sphincter pupillary muscles and ciliary muscles
Describe the ophthalmic artery
- it is a branch of the internal carotid artery
- travels with the optic nerve through the optic canal
Describe the central retinal artery
- it pierces the optic nerve and travels in the middle of the optic nerve to supply the retina
Describe the ophthalmic veins
- there is a superior and inferior ophthalmic vein
- they travel through the superior orbital fissure
- they drain into the cavernous sinus
- they anastomose with the angular vein of the facial vein
Describe the location of the lacrimal nerve
it sits on top of the lateral rectus muscle
Describe the location of the frontal nerve
it sits on top of the levator palpebrae superioris
Where is the superior rectus muscle found in relation to the levator palpebrae superioris ?
the superior rectus is found below the the levator palpebrae superioris
