Orbit Flashcards
What are the bones of the orbit (skull)?
Anterior Cranial Fossa
Middle Cranial Fossa
Posterior Cranial Fossa
Maxillary Sinus (Inferior)
Nasal Cavity (Medial)
What are the dimensions of the orbit?
35mm H x 40mm V
30mL volume
45-55mm axial length
25mm between
From where to where is the axial length of the orbit measured?
Apex (optic canal) to Base (orbital margin)
Describe the angles and positioning of the medial walls, lateral walls, optical axis, & orbital axis.
Medial walls separated by 25mm
Lateral walls form 90< and expose the eyes laterally to increase visual field
Orbital axis forms 45<
Optical axis is the axis that eyeballs look at
What are the holes/bones of the orbit from top to bottom?
Supraorbital notch
Superior orbital fissure
Optic canal
Lacrimal fossa
Inferior orbital fissure
Infraorbital foramen
What are the nerves of the superior orbital fissure?
Lacrimal Nerve
Frontal Nerve
Trochlear Nerve (4 motor)
Superior division of the oculomotor nerve (3)
Nasocilliary Nerve
Inferior division of the oculomotor nerve (3)
Abducens nerve (6 motor)
Superior ophthalmic vein
Part of inferior ophthalmic vein
What is in the Tendinous ring of Zinn (muscle cone)?
Optic canal
Optic nerve (2)
Ophthalmic artery (branch of interior carotid)
What are the nerves of the inferior orbital fissure?
Ganglionic branches (maxillary nerve)
Infra-orbital nerve (5b)
zygomatic nerve (5b)
Inferior ophthalmic veins
Infra-orbital artery
Infra-orbital vein
What nerves are outside vs. inside the muscle cone?
Outside: L,F,T
Inside: S (levator, superior recuts) ,A,N,I (inferior oblique, inferior/medial rectus, pupillary fibers)
SO4 LR6, everything else 3
What movements do the lateral, medial, superior and inferior rectus innervate?
Abduction
Adduction
Elevation
Depression
What movements do the superior and inferior oblique innervate?
Intorsion
Extorsion
What 3 muscles innervate lid position and what do they do?
Orbicularis oculi (7): close lid
Levator palpebrae superioris (3 sup.): elevate lid
Muller muscle (3 inf.): depression
What lid muscle is controlled by the sympathetic NS?
Muller muscle
What muscles form the muscle cone?
The recti muscles
Which muscle does not originate from the back of the orbit?
Inferior oblique
What is the purpose of the eye and visual system?
Transform light energy into neural signal to be perceived by the brain.
What are the dimensions if the eyeball?
23.5mm H
24mm V
23-24mm axial length
Compare steepness and radius of curvature of the sclera and cornea.
Cornea is steeper
Sclera has a higher radius of curvature (11.5mm vs. 7.8mm)
What are the volumes of the anterior chamber, posterior chamber, vitreous, and total volume?
250ul anterior chamber
60ul posterior chamber
Vitreous 5-6mL
Total= 6.5mL
What is the mass of the eyeball?
7.5g
What is the carotid system?
Carries blood from heart to eye
What is the ophthalmic artery?
First major branch of the internal carotid artery
Where does the carotid artery branch what does it branch into?
Branches at the carotid bifocation into the external and internal carotid
What is the carotid system?
Circulates the eye via ophthalmic artery
Anterior 2/3 of cerebral hemispheres
What is the vertebrobasilar system?
Poster 1/3 of cerebral hemispheres including the occipital lobe
Brainstem (cranial nerves)
Cerebellum
Circle of Willis
Links blood supply in the middle of the brain
Retinal blood supply
2 blood supplies to satisfy high metabolic demand
