26 - Eye and Orbit Flashcards
What bones make up the margin of the orbit?
- frontal
- maxilla
- zygomatic
What bones make up the walls of the orbit?
- frontal
- maxilla
- zygomatic
- lacrimal
- ethmoid
- sphenoid
- palatine (minor)
What are the main openings into the orbit?
- superior orbital fissure
- inferior orbital fissure
- nasolacrimal canal
- optic canal
What structures pass through the inferior orbital fissure?
Inferior ophthalmic vein
What structures pass through the superior orbital fissure?
- trochlear nerve
- abducent nerve
- opthalmic nerve branches (CNV1)
- occulomotor nerve
What structures pass through the optic canal?
- optic nerve
- opthalmic artery
What structures pass through the nasolacrimal canal?
Nasolacrimal duct
Which branches of CN V1 pass through the superior orbital fissure?
- frontal
- lacrimal
- nasocillary
Which branches of CN III pass through the superior orbital fissure?
- superior
- inferior
Describe the structure of the optic nerve.
- surrounded by cranial meninges
- contains central retinal artery and vein
What are the contents of the orbit?
- eyeball
- retrobulbar fat
- optic nerve
- extraocular muscles
- eyelids and lacrimal apparatus
Describe how the optic nerve enters the skull.
- leave the brain as the two optic tracts
- meet at the optic chiasm as they enter the skull
- enter the skull as the two optic nerves
What is papilloedema?
- raised intracranial pressure is transmitted to the meninges surrounding the eye
- venous drainage of the eye slows
- causes swelling of the optic disc
What is amaurosis fugax?
- when the central retinal artery becomes occluded
- painless and temporary loss of vision
Describe how injury to the optic nerve affects the visual field.
- vision is lost completely in one eye
- nerve from both sides of the brain are damaged
Describe how injury to the optic chiasm affects the visual field.
- tunnel vision
- lateral vision is lost as the nerves from both sides cross over
Describe how injury to the optic tract affects the visual field.
- field of vision on the contralateral side is lost
- injury before the tract crosses over
Where is the lacrimal gland located?
Upper lateral corner of orbit
Describe the drainage of the lacrimal gland.
- tears released in the upper lateral corner of the eye
- washed over the eye by the orbicularis oculi
- form a lake in the medial corner of the eye (lacrimal caruncle)
- drain via puncta to the lacrimal sac and then to the nasolacrimal duct
- drains into inferior nasal meatus
Describe the parasympathetic innervation of the lacrimal gland.
- preganglionic fibres from nervus intermedius (CN VII)
- travel in greater petrosal nerve, then nerve of pterygoid canal
- arrive at the pterygopalatine ganglion
- postganglionic fibres via zygomatic branch (CN V2) to lacrimal gland
What are the extraocular muscles?
- superior oblique
- inferior oblique
- medial rectus
- lateral rectus
- superior rectus
- inferior rectus
- levator palpebrae superioris
Describe the origin and insertion of the extraocular muscles.
- all originate from the common tendinous ring at the posterior of the orbit
- EXCEPT the inferior oblique which originates from the maxilla
- all insert to the sclera
What muscle pulls the eye medially?
Medial rectus
What muscle pulls the eye medial and superiorly?
Superior rectus
What muscle pulls the eye laterally?
Lateral rectus
What muscle pulls the eye lateral and superiorly?
Inferior oblique
What muscle pulls the eye inferiorly?
Inferior rectus and superior oblique
What muscle pulls the eye superiorly?
Superior rectus and inferior oblique
What muscle pulls the eye laterally and inferiorly?
Superior oblique
What muscle pulls the eye medially and inferiorly?
Inferior rectus
Describe the innervation of the extraocular muscles.
- LR6 SO4 AO3
- lateral rectus = abducent
- superior oblique = trochlear
- all others = occlumotor
Describe the oculomotor nerve.
- supplies extraocular muscles
- supplies parasympathetic fibres for pupillary construction
- supplies sympathetic fibres to the smooth muscle fibres in levator palpebrae superioris
How does injury to the oculomotor nerve present?
- mydriasis (dilated pupil) by loss of parasympathetic constriction
- ptosis (drooping eyelid) by loss of function of levator palpebrae superioris
- eye turned downwards and outwards (unopposed SO and LR muscles still acting)
What are the outer layers of the eyeball?
- sclera (replaced anteriorly by the cornea)
- choroid (vascular)
- retina
Describe the structure of the eyeball.
- cornea outermost layer
- anterior and posterior chamber are separated by the iris
- the chambers communicate via the pupil
- chambers contain aqueous humour
- lens innermost
- vitreous chamber makes up bulk of eye, filled with vitreous humour
Describe where the visual and non visual parts of the retina are located.
- visual parts on medial, lateral and posterior walls
- non visual part on anterior wall
What is aqueous humour?
- secreted by ciliary body in the choroid layer of the eyeball
- reabsorbed by the scleral venous sinus
What is glaucoma?
- excess pressure due to aqueous humour
- can be treated using drugs that constrict the pupil and pull the sinus open
What are the muscles found in the anterior eye and how are they controlled?
- ciliaris (in ciliary body, parasympathetic)
- dilator pupillae (sympathetic)
- sphincter pupillae (parasympathetic)
- all innervated by CN III
