Ophthalmology - Pupil Disorders Flashcards
What are circular muscles and dilator muscles responsible for?
Circular muscles
Pupil constriction - Parasympathetic stimulation - ACh
Fibres travel along CNIII
Dilator muscles
Pupil dilation - Sympathetic stimulation - Adrenaline
What can cause an irregular pupil shape?
Trauma to sphincter muscles
Anterior uveitis
Acute angle-closure glaucoma
Rubeosis iridis
Coloboma
Tadpole pupil
Each condition has distinct characteristics affecting pupil shape
What causes a tadpole pupil?
Muscle spasm in part of the dilator muscle of iris
Temporary
Associated with migraines and Horner syndrome
List some causes of mydriasis (dilated pupil)
- Congenital
- Stimulants (e.g., cocaine)
- Anticholinergics (e.g., oxybutynin)
- Trauma
- Third nerve palsy
- Holmes-Adie syndrome
- Raised intracranial pressure
- Acute angle-closure glaucoma
List some causes of miosis (constricted pupil)
- Horner syndrome
- Cluster headaches
- Argyll-Robertson pupil (neurosyphilis)
- Opiates
- Nicotine
- Pilocarpine
What are the signs of third nerve palsy?
- Ptosis (drooping upper eyelid)
- Dilated non-reactive pupil
- Divergent strabismus (squint) in the affected eye, down and out position
Why do you get a down and out position of the eye in CNIII palsy?
All extraocular muscles except lateral rectus and superior oblique are controlled by CNIII
Superior oblique pulls th eye downwards and lateral rectus pulls the eye outwards
What causes ptosis in third nerve palsy?
Loss of function of levator palpebrae superioris
Why does CNIII cause a dilated, non-reactive pupil?
Parasympathetic fibres innervate circular muscles of the iris
Thefore causing a dilated pupil
Why does pupil sparing suggest microvascular complication?
Parasympathetic fibres are not compressed therefore due to :
- Diabetes
- Hypertension
- Ischaemia
What can cause compression of the oculomotor nerve?
- Tumour
- Trauma
- Cavernous sinus thrombosis
- Posterior communicating artery aneurysm
- Raised intracranial pressure
What does the oculomotor nerve pass through?
Cavernous sinus
Close to posterior communicating artery
What is Horner syndrome characterized by?
- Ptosis
- Miosis
- Anhidrosis (loss of sweating)
Can also have enopthalmos (sunken eye)
What is the path of sympathetic nerves?
Sympathetic nerves arise from the spinal cord in the chest as pre-ganglionics
Pre-ganglionics enter the sympathetic ganglion at the base of neck and exis as post-ganglionic nerves
Post-ganglionics travel with the ICA
What is the significance of anhidrosis in Horner syndrome?
Central lesions occur before nerves exit the spine,anhidrosis of :
- Arm
- Trunk
- Face
Pre-ganglionic lesions
Face
Post-ganglionic
Does not cause anhidrosis
