Eyes & orbit Flashcards
What is the orbit?
Socket in facial skeleton in which the eye lies.
What is the structure of the orbit?
- Pyramidal in shape, with the base being the rim and the apex pointing posteromedially and containing the optic canal.
- The medial walls are parallel to each other while the lateral walls are perpendicular to each other.
What are the bones that make up the orbit?
- Maxilla
- Zygomatic bone
- Frontal bone
- Ethmoid
- Lacrimal bone
- Sphenoid
- Palatine bone
What are the boundaries of the orbit?
- Roof:
1. Orbital plate of frontal bone
2. Lesser wing of sphenoid - Floor: Maxilla
- Lateral walls:
1. Zygomatic bone
2. Greater wing of sphenoid - Medial walls:
1. Ethmoid (largest contributor)
2. Lacrimal bone
3. Maxilla
4. Sphenoid
What are the key features of the medial wall of the orbit?
- Medial lies the ethmoidal air cells.
- Ethmoidal foramina: Through which the ethmoidal nerves and vessels pass.
- Lacrimal fossa: In which the lacrimal sac lies. Inferior aspects also has foramen through which nasolacrimal duct opens into nasal cavity.
What are the key features of the of the floor orbit?
- Inferior lies the maxillary sinus.
- Inferior orbital fissure (separating lateral wall from floor): Through which passes:
1. Zygomatic branch of maxillary nerve
2. Ascending branches from pterygopalatine ganglion
3. Infra-orbital vessels
4. Inferior opthalmic vein (sometimes)
What are the key features of the lateral wall of the orbit?
Superior orbital fissure, which transmits (from superior to inferior):
- Superior opthalmic vein
- Lacrimal nerve
- Frontal nerve
- Trochlear nerve [IV]
- Superior division of [III]
- Nasociliary nerve
- Abducent nerve [VI]
- Inferior division of [III]
- Inferior opthalmic vein (sometimes)
What are the groups of muscles in the eyes?
- Intraocular muscles
- Extraocular muscles
- Levator palpebrae superioris
What are the intraocular muscles?
- Ciliary muscles: Used in accommodation
- Pupillary dilators/constrictors: Dilates/constricts pupils
What are the extraocular muscles?
- Superior rectus: Adducts & elevates eyes
- Inferior rectus: Adducts & depresses eyes
- Medial rectus: Adducts eyes
- Lateral rectus: Abducts eyes
- Superior oblique: Abducts & depresses eyes
- Inferior oblique: Abducts & elevates eyes
What is the common origin of the recti muscles of the eyes?
Tendinous ring around the optic canal (Annulus of Zinn)
What is the innervation of the extraocular muscles?
- All muscles except superior rectus and lateral oblique are innervated by the oculomotor nerve [III].
- Superior oblique innervated by the trochlear nerve [IV].
- Lateral rectus innervated by the abducent nerve [VI].
What is the arterial supply of the eyes?
- Eyes are supplied by the opthalmic artery, which enters orbit through optic canal.
- Branches of the opthalmic artery include:
1. Central artery of the retina: Enters optic nerve and travels in its centre.
2. Lacrimal artery: Given off when artery passes lateral to optic nerve.
3. Anterior ciliary arteries: Supplies orbital muscles, sclera and conjunctiva.
4. Long ciliary arteries: Supplies iris, ciliary body and choroid.
5. Short posterior ciliary arteries: Supplies chorid and ciliary processes.
What is significant about the recurrent meningeal branch of the lacrimal artery?
Forms anastomoses with anterior branch of middle meningeal artery, forming one of the few anastomotic connections between the ICA and ECA.
What is the venous drainage of the eyes?
- Superior opthalmic vein: Passes through superior orbital fissure and drains into cavernous sinus.
- Inferior opthalmic vein: Has one of 3 fates:
1. Joins superior opthalmic vein and drains into cavernous sinus
2. Passes separately through superior orbital fissure to drain into the cavernous sinus
3. Passes through inferior orbital fissure to drain into the pterygoid venous plesus
