Pupil Disorders Flashcards
What is the cause of pupil constriction?
Circular muscles in the iris which cause constriction
These muscles are stimulated by the PS nervous system using acetylcholine as a neurotransmitter
Where do the fibres of the Parasympathetic system which innervate the eye travel along?
Oculomotor (CN III) nerve
How are dilator muscles of the pupil arranged?
Like spokes on a bicycle wheel
What is pupil dilation stimulated by?
Sympathetic nervous system using adrenalin as a neurotransmitter
Possible causes of abnormal pupil shape?
- Trauma to the sphincter muscles in iris
- Anterior uveitis can cause adhesions in iris
- AACG
- Rebeosis Iridis (usually assoc with poorly controlled diabetes)
- Coloboma
- Tadpole pupil (assoc with migraine)
Causes of mydriasis?
- 3rd nerve palsy
- Holmes Adie syndrome
- Raised ICP
- Congenital
- Trauma
- Stimulants eg cocaine
- Anticholinergics
Causes of miosis?
- Horner’s syndrome
- Cluster headaches
- Argyll-Robertson pupil (Neurosyphilis)
- Opiates
- Nicotine
- Pilocarpine
What is mydraisis?
Pupil dilation
What is miosis?
Pupil constriction
Presentation of 3rd nerve palsy?
- Ptosis
- Divergent strabismus
- Dilated non-reactive pupil
- ‘Down and out’ eye position of affected eye
What does the oculomotor nerve supply?
Supplies all extraocular muscles except lateral rectus and superior oblique
What happens when muscles aren’t getting signals from CN III?
They move outward and downward
The oculomotor causes ptosis how?
The nerve also supplies the palpebrae superioris, which is responsible for lifting upper eyelid
Which type of fibres does the oculomotor also contain?
Parasympathetic which innervate sphincter muscles of iris, resulting in 3rd nerve palsy causing a dilated fixed pupil
The jouney of CN III?
Travels directly from the brainstem to the eye in a straight line
Travels through cavernous sinus & close to posterior communicating artery
What 2 things can cause compression on the CN III nerve resulting in 3rds nerve palsy?
Cavernous sinus thrombosis
Posterior communicating artery
Causes of 3rd nerve palsy with sparing of pupils ?
Diabetes
Hypertension
Ischaemia
What does sparing of pupils in 3rd nerve palsy indicate?
Microvascular causes as PS fibres are spared
What is full CN III compression caused by?
Compression of the nerve, including PS fibres compression
What may full CN III palsy be caused by?
Idiopathic Tumour Trauma Cavernous sinus thrombosis Raised ICP Posterior communicating artery aneurysm
What is Horner’s syndrome?
Triad of miosis, anhidrosis and ptosis
Cause of Horner’s syndrome?
Caused by damage to the sympathetic nervous system supplying face
How can the location of Horner’s syndrome be determined?
The anhidrosis
What do central lesions cause in Horner’s syndrome?
Central lesions cause anhidrosis of arm and trunk aswell as face
What location of Horner’s syndrome causes anhidrosis of just the face?
Pre-ganglionic
What type of anhidrosis does post ganglionic Horner’s syndrome cause?
NO anhidrosis
How can Horner’s syndrome be remembered?
4 S’s (Sentral), 4 T’s (Torso/Pre-ganglionic), 4 Cs (Cervical/Post ganglionic)
What are sympathetic nerves called when they arise from spinal cord in the chest?
Pre-ganglionic
Where do sympathetic nerve enter the sympathetic ganglion?
At the base of the neck and they exit as post-ganglionic nerves
What do post-ganglionic nerves travel alongside?
Internal carotid artery
Causes of central lesions in Horner’s syndrome?
4 S’s
- Stroke
- Multiple sclerosis
- Swelling (tumours)
- Syringomyelia (cyst in spinal cord)
Causes of pre-ganglionic lesions?
4 T’s
- Tumour (Pancoast’s)
- Trauma
- Thyroidectomy
- Top rib (cervical rib growing above 1st rib & clavicle)
Causes of post-ganglionic lesions?
4 C’s
- Carotid aneurysm
- Carotid artery dissection
- Cavernous sinus dissection
- Cluster headache
What type of Horner’s syndrome is associated with heterochromia?
Congenital Horner Syndrome
Investigation for Horner’s syndrome?
Cocaine eye drops
Low concentration adrenalin eye drop (0.1%)
What do cocaine eye drops convey in the investigation of Horner’s syndrome?
Cocaine acts on the eye to stop noradrenaline re-uptake @ neuromuscular junction
- Tis causes normal eye to dilate because there is more NA stimulating dilator muscles of iris
- In Horner’s syndrome, nerves aren’t releasing NA, so blocking reuptake doesn’t make a difference
How do adrenalin eye drops work as an investigation?
Will dilate a normal pupil BUT won’t dilate a Horner Syndrome pupil
What is Holmes Adie Pupil?
Unilateral dilated pupil that is sluggish to react
Presnetation of Holmes Adie Pupil?
Slow dilation of the pupil following constriction
Over time the pupil will get smaller
Cause of Holmes Adie pupil?
Damage to post-ganglionic PS fibres
Exact cause unknown but most likely viral
What is the Argyll Robertson pupil?
Constricted pupil that accommodates when focusing on a near object but does not react to light
Often irregularly shaped
What disease is Argyll Robertson pupil a common finding in?
Neurosyphilis
What is another common name for Argyll Robertson pupil?
Prostitutes pupil
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Because of relation to syphilis and because it accommodates but doesn’t react
