Orbit, eye, ear Flashcards
What would you see with a trochlear nerve palsy?
(1.) Loss of function of the superior oblique (SO = down and abduct and intorsion)
(2. ) Signs (right eye is affected):
- Ask pt to look forward: affected eye will have an upward gaze
- Ask pt to look right = affected eye elevates as it moves medially, diplopia may be seen.
- Ask pt to look left = no obvious sign.
- Patients can also develop a head tilt away from the affected side.
- diplopia is exacerbated when looking downwards and inwards (such as when reading or walking down the stairs)
- impaired intorsion
(3.) Commonly caused by microvascular damage from diabetes mellitus or hypertensive disease.
What would you see with an abducens nerve palsy?
(1.) Weakness of lateral rectus muscle -> impaired abduction of the eye
(2. ) Signs:
- diplopia
- affected eye resting in adduction (due to unopposed activity of the medial rectus)
- inability to abduct the eye.
(3.) caused by any structural pathology which leads to downwards pressure on the brainstem (e.g. space-occupying lesion).
What would you see with an oculomotor nerve palsy?
(1.) CN3 innervates levator palpebrae superioris, superior rectus, inferior rectus, medial rectus and inferior oblique (MOTOR) + supplies the sphincter pupillae and ciliary muscles causing constriction (PNS).
(2. ) Signs:
- ptosis
- down and out eye
- dilated pupil
(3. ) Causes: RICP, posterior communicating artery aneurysm, cavernous sinus infection or trauma.
- diabetes, multiple sclerosis, myasthenia gravis and giant cell arteritis.
Describe the innervation of the eye muscles
(1.) CN3 = LPS, IO, SR, IR, MR (motor), sphincter pupillae + ciliary muscles (PNS)
(2. ) CN4 = SO
(3. ) CN6 = LR
(4. ) CN7 = Lacrimal gland
(5.) Superior cervical ganglion via T1 = dilator pupillae muscles (SNS)
Describe the function of opthalamic nerve/CNV1
(1. ) Sensation to forehead + nose
(2. ) At the SOF: CNV1 splits into the frontal nerve (centrally) and lacrimal nerve (laterally) in the orbit
(3. ) Frontal nerve = mucosa of frontal sinus
(4. ) Lacrimal nerve = lacrimal gland and upper eyelid
Note lacrimal nerve supplies sensory innervation whereas CN7 supplies PNS innervation.
Describe structure of the eye (7)
(1. ) Cornea = transparent covering of iris (coloured part) and pupil.
(2. ) Lens = Found behind the cornea, iris, pupil. Focuses light rays onto the retina.
(3. ) Retina = transmits image info received from lens to optic nerve for brain to process
(4. ) Ciliary = Holds the lens in place, changes shape of lens.
(5. ) Sclera = white part of eye that protects the eyeball
(6. ) Optic disc = back of retina where optic nerve, central retinal artery and vein enter and radiate the eyeball. This area has no photo-receptors so it is insensitive to light
(7. ) Optic nerve = transmits info to thalamus
Describe the drainage from lacrimal glands into the nose
Lacrimal gland secretes lacrimal fluid (tears) -> lacrimal punch -> lacrimal sac -> nasolacrimal duct -> drains into inferior meatus
Describe the structure of the ear
Ear is divided into the external, middle, internal parts.
External Ear
- Sound is collected hear and transmitted along the external acoustic meatus, which conducts sound to the tympanic mb
MEC
- This is ‘air filled’, where ossicles vibrate
- Made up of: malleus, incus, stapes
- Mucus/infections in this area will lead to deafness
- CN7 branch travels through the MEC
Internal Ear
- ‘fluid filled’, embedded in the petrous part of the temporal bone
- made up of semicircular canals, vestibule, cochlea
- SCC = 90 degrees to each other signals to the brain about direction, speed of rotation of the head
- Cochlea = organ of hearing, movement of ciliary is interpreted by the brain
Main action of the levator palpebrae superioris
Elevates superior eyelid
Superior oblique action
Abducts, depresses and rotates eye medially (intorsion)
Inferior oblique action
Abducts, elevates and rotates eye laterally (extorsion)
Superior rectus
Elevate and adduct
Inferior rectus
Depress and adduct
Medial rectus
Adducts
Lateral rectus
Abducts
