Ophthalmology - Pupil Disorders Flashcards
Outline how pupillary constriction works
-Parasympathetic nervous system (using acetylcholine as a neurotransmitter) travelling around occulomotor nerve stimulate constrictor pupillae muscles (circular muscles in the iris)
Outline how pupillary dilation works
-Sympathetic nervous system uses adrenalin as a neurotransmitter to stimulate the dilator pupillae muscles
Give a differential for conditions that cause an abnormally shaped pupil (5)
- Trauma to sphincter muscles (eg cataract surgery)
- Anterior uveitis: adhesions can occur in the iris and put traction on pupils
- Acute angle closure glaucoma: can cause ischaemia of the muscles of iris, usually resulting in oval shape.
- Rubeosis iridis: neovascularisation of the pupil (DM induced)
- Coloboma: congenital malformation (hole in iris)
Give a differential for mydriasis (7)
Dilated pupil
- Occulomotor nerve palsy
- Holmes-Adie syndrome
- Raised ICP
- Congenital
- Trauma
- Stimulants: cocaine
- Anticholinergics
Give a differential for miosis (6)
Constricted pupil
- Horner’s syndrome
- Cluster headaches
- Opiates
- Nicotine
- Pilocarpine
Describe the effects of a 3rd nerve palsy
- Eye down and out: unopposed pull of lateral rectas and superior oblique
- Ptosis: LPS affected
- Dilated fixed pupil: parasympathetic fibres also affected (surgical 3rd nerve palsy)
What type of 3rd nerve palsy would spare the pupil? Give a differential
- Pupil sparing suggests microvascular cause as parasympathetic fibres are not affected
- Diabetes, HTN, ischaemia
Give a differential for a surgical 3rd nerve palsy
Surgical: physical compression of the nerve
- Idiopathic
- Tumour
- Trauma
- Cavernous sinus thrombosis
- Posterior communicating artery aneurism
- Raised ICP
What are the 3 classic symptoms of Horner’s syndrome?
- Ptosis
- Miosis
- Anhidrosis
- May have enophthalmos
- *Light and accommodation reflexes are not affected
How can you used anhydrous is to locate the lesion causing Horner’s syndrome?
- Central lesions: anhidrosis of arm and trunk as well
- Pre-ganglionic lesions (from spinal cord to sympathetic ganglion): anhidrosis of the face
- Post-ganglionic lesions (from post-ganglion via ICA to face): do not cause anhidrosis
Give 4 causes for central lesions (4S)
- Stroke
- MS
- Swelling (tumours)
- Seryngomyelia
Give 4 causes for pre-ganglionic lesions (4T)
- Tumour: pancoast
- Trauma
- Thyroidectomy
- Top rib: cervical rib
Give 4 causes for post-ganglionc lesions (4C)
- Carotid aneurism
- Carotid artery dissection
- Cavernous sinus thrombosis
- Cluster headache
Explain how the cocaine eye drop test works for Horner’s syndrome
- Cocaine acts on the eye to stop noradrenalin re-uptake at the neuromuscular junction.
- This causes the eye to dilate because there is more noradrenalin stimulating the dilator muscles of the iris.
- In Horner’s: the nerves are not releasing noradrenalin to start with, so blocking re-uptake doesn’t make a difference and there is no reaction (dilation) of the pupil.
What is the Holmes Adie pupil?
- Differential for dilated pupil, also known as tonic (slow) pupil
- Opposite of Horner’s: parasympathetic pathway is knocked out.
- Unilateral dilated pupil that is sluggish to react to light with slow dilation of pupil after constriction.
- Cause unknown but could be viral.
