Orbit Flashcards
Name the 3 bones forming the majority of the orbit
- Frontal
- Maxilla
- Zygomatic
What are the orbits
Bilateral bony cavities in the facial skeleton that resemble hollow, quadrangular pyramids
What is related to the notch of the frontal bone on the superior ridge of the orbit
Supraorbital artery and nerve
Name the orbital foramen the maxilla forms, and the structure that passes through
Infraorbital foramen; infraorbital branch of CNV2 exits the skull to provide sensory information to the face
Name the 3 minor bones that contribute to the bony wall of the orbit
- Ethmoid
- Lacrimal
- Sphenoid (greater and lesser wings)
Name the 5 contents of the orbit
- Eyeball
- Fat and connective tissues
- Extraocular muscles
- Nerves
- Blood vessels
What structure carries excess lacrimal fluid into the nasal cavity
The nasolacrimal duct
What are the eyelids covered by externally, and internally
Externally = thin skin Internally = transparent mucous membrane, the palpebral conjunctiva
What is the palpebral conjunctiva continuous with on the surface of the eyeball
The bulbar conjunctiva
What ligaments support the corners of the eye
Medial and lateral palpebral ligaments
Name the dense connective tissue that forms the eyelids
The superior and inferior tarsus
What are the functions of the tarsal plates
- Physically protects the eye
2. Releases oily and watery secretions to lubricate the surface of the eye (through tarsal glands)
What ligaments support the eyeball
The suspensory ligaments
What is the action of the check ligaments
They restrict the movements of the medial and lateral recti
Name the 2 layers of the outer coat of the eyeball
- Cornea (fibrous layer covering anterior 1/6th)
2. Sclera (fibrous layer covering posterior 5/6th)
Name the 3 layers of the vascular (middle) coat
- Iris
- Ciliary body
- Choroid
Name the single layer of the inner coat
Retina
What is the choroid
Dark red layer between the sclera and the retina; lines most of the sclera
What is the ciliary body
Ring-like thickening of the vascular layer posterior to the corneoscleral junction (muscular and vascular)
What are the functions of the ciliary body
- Connects the choroid with the circumference of the iris
2. Provides attachment for the lens
What is the iris
Contractile diaphragm on the anterior surface of the lens with a central aperture, the pupil, for transmitting light
Name the two involuntary muscles that control the size of the pupil
- Sphincter pupillae (parasympathetic) decreases its diameter
- Dilator pupillae (sympathetic) increases its diameter
Name the two layers of the optic part of the retina
- Neural layer: light receptive
2. Pigmented layer: reduces scattering of light in the eyeball (light-absorbing property)
What is the space between the lens and the cornea called, and what is it filled with
The anterior chamber, filled with aqueous humor
What produces aqueous humor, and where
The ciliary body in the posterior chamber
What is the function of the aqueous humor
It helps to maintain intraocular pressure
Where does aqueous humor drain
Into the corneoscleral junction, via the canal of Schlemm
What causes sphincter-like contraction of the ciliary muscle
Parasympathetic stimulation via the oculomotor nerve (CN III)
Where is the vitreous humor located
The meshes of the vitreous body in the posterior 4/5ths of the eyeball posterior to the lens
What are the functions of the vitreous humor
- Transmits light
- Holds the retina in place
- Supports the lens
What do the extraocular muscles function as
Move the eyeball as a whole or raise the upper eyelid
How many extraocular muscles are there, and name them
There are 7:
- Levator palpebrae superioris
- Superior recti
- Inferior recti
- Medial recti
- Lateral recti
- Superior oblique
- Inferior oblique
Where do the recti muscles pass from, and to
Annular ring to the sclera
Where do the superior, and inferior obliques pass from, and to
Lesser wing of the sphenoid and the orbital floor, respectively, to the sclera
Describe the innervation to the extraocular muscles
LPS = oculomotor (CN III) SR = oculomotor (CN III) IR = oculomotor (CN III) MR =oculomotor (CN III) LR = abducent (CN VI) SO = trochlear (CN IV) IO = oculomotor (CN III)
Describe the action of the extraocular muscles
LPS = raises the upper eyelid SR = elevation, abduction, intorsion IR = depression, abduction, extorsion MR = adduction LR = abduction SO = intorsion, depression, abduction IO = extorsion, elevation, abduction
What area do the nerves have to pass through before they reach the superior orbital fissure
The cavernous dural venous sinus
Why is the abducent nerve the ‘odd one out’ as it passes through the cavernous dural venous sinus
It passes close by to the internal carotid artery; the others pass along the walls close to the dura
Describe the exit process of the optic nerve out of the orbit
Optic nerve formed and myelinated as it passes through the lamina cribrosa of the sclera (through the optic disc)
What do the optic nerves form before they form the optic tracts
Chiasm over the pituitary fossa then optic tracts are sent to the brain (e.g. thalamus)
What is the function of the optic radiations
Take information to be processed in the primary visual cortex
What are the 3 terminal branches of CNV1
- Frontal
- Nasociliary
- Lacrimal
Describe the pathway of the terminal branches of CNV1
Pass through the superior orbital fissure and supply structures related to the anterior orbit, face, and scalp
What are the terminal branches of the frontal branch of CNV1 (and what do they supply)
- Supraorbital
- Supratrochlear
Pass onto the face to supply sensory innervation to the skin of the forehead
Name the branches of the nasociliary branch of CNV1
Ethmoidal branches which pass through the ethmoid bone
What is the function of the lacrimal branch (nerve)
Acts as a carrier for parasympathetic secretomotor fibres from the facial nerve
What is the main supply to the orbit, and how does it enter the orbit
Ophthalmic (from internal carotid artery); it enters the orbit through the optic canal with the optic nerve
Where does the infra-orbital artery branch from
The external carotid artery
Name the branches of the ophthalmic artery
Forehead and scalp: 1. Supraorbital 2. Supratrochlear 3. Zygomaticotemporal Nose: 1. Dorsal nasal 2. Ethmoidal
Describe the venous drainage of the orbit
Super and inferior ophthalmic veins
Describe the pathways of the orbital veins
Can pass through the:
- Superior orbital fissure and enter the cavernous sinus
- Inferior orbital fissure and enter the pterygoid venous plexus
- Facial vein
What specific veins drain the vascular layer of the eyeball
The vorticose veins, and into the inferior ophthalmic vein
Describe the innervation to the lacrimal apparatus
From facial nerve (CN VII) carried in trigeminal nerve (CNV1)
How are the tears collected across your eye
Gathered through lacrimal punctum into the lacrimal canaliculi, and then into a membrane lined space called the lacrimal sac
