Orbit Flashcards
Bones of the orbit
Top- Frontal
Lateral- zygoma and greater wing of sphenoid
Bottom - maxilla
Medial- front process of maxilla, lacrimal bone, orbital plate of ethmoid and lesser wing of sphenoid
Orbital foramina and what passes through them
Optic canal: Optic nerve (II) and ophthalmic artery travel through the optic canal
Inferior orbital fissure: Maxillary division of the trigeminal nerve (V2) and the infraorbital vessels
Superior orbital fissure:
- Ophthalmic division of the trigeminal nerve (V1)
- Oculomotor nerve (III)
- Trochlear nerve (IV)
- Abducens nerve (VI)
- Ophthalmic vessels and Sympathetic fibres (tend to run with the vessels
Muscles of the eye and their supply
Inferior, superior and medial recti supplied by oculomotor (III)
Lateral rectus supplied by abducens (VI)
Superior oblique- trochlear
Inferior oblique- oculomotor
Levator Palpebrae Superioris-oculomotor
Function of each muscle of the eye
Inferior rectus- depressor and adduct Superior rectus- elevator and adduct Lateral rectus- adductor Medial rectus- abductor Superior oblique- depressor and abductor Inferior oblqiue- elevator and abductor Levator palpebrae superioris-move upper eyelid
Testing muscle of the eyes action
Two muscles (IR, SO) are involved in depressing the eye.
To test function, you adduct or abduct the eye, before asking the patient to look down.
- When the eye adducts towards the midline, the only muscle contributing to depression then is the SO
- When the eye abducts away from the midline, the only muscle contributing to depression is the IR
Nerves of the orbit
- Optic nerve – made up of the axons from the ganglion cells in the retina
- Oculomotor nerve (has 2 rami) – Motor fibres to MR, SR, IR, IO & LPS and parasympathetic fibres
- Trochlear nerve – Motor fibres to SO
- Abducens – Motor fibres to LR
- Ophthalmic (V1) branches
Route of the ophthalmic nerve
Travels laterally to the cavernous sinus and gives rise to the recurrent tentorial branch (which supplies the tentorium cerebelli).
It then exits the cranium via the superior orbital fissure, where it divides into its 3 branches: frontal nerve, lacrimal nerve and nasociliary nerve
Ophthalmic divisions
- Lacrimal nerve - goes out to the lacrimal gland area)
- Frontal (divides into the supratrochlear and supraorbital nerves -sensory innervation of skin)
- Nasociliary (branch to ciliary ganglion, ethmoidal branch, infratrochlear branch)
What is supplied by the ophthalmic artery
- Central artery of the retina
- Muscular branches
- Ciliary branch
- Lacrimal branch
- Supratrochlear branch
- Supraorbital branch
Ophthalmic veins drain to
- Superior ophthalmic vein drains back into the cavernous sinus – potential route of infection
- Inferior ophthalmic vein drains back into the pterygoid plexus – no passage into cranial cavity
Position of the lacrimal gland
Anterolateral superior orbit
Route of parasympathetic supply of lacrimal gland
Facial nerve->Pterygopalatine ganglion -> crosses over to maxillary branch via zygomaticotemporal nerve -> lacrimal nerves -> Gland
Position of lacrimal sac and where it drains
The lacrimal sac is in the medial canthus of the eye
The lacrimal sac drains into the nose via the nasolacrimal duct into the inferior meatus of the nose
Autonomic innervation of the eye
Parasympathetic:
Optic nerve and tract -> pretectum -> Edinger-Westphal nucleus (parasympathetic) -> oculomotor nerve -> ciliary ganglion -> sphincter pupillae and ciliary muscles for miosis and lens thickening.
Sympathetic: T1 -> superior cervical ganglion -> carotid plexus -> branches of ophthalmic nerve -> dilator pupillae, tarsal muscle (part of levator palpebrae superioris) and blood vessels.
Testing for Relative Afferent Pupillary Defect
Elicited by the swinging torch test – alternating stimulation of right and left eye with light, at least 3 seconds per eye. Both pupils constrict when light swings to the left undamaged side. Both pupils paradoxically dilate when light swings to the right damaged side.
