Pupils and Horner syndrome flashcards
16 high-yield MRCP Part 1 cards from the Intellect Medicos Ophthalmology course. Try to answer each question before you open it — then study them properly with spaced repetition, which brings each card back just before you would forget it.
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What is the first-line pharmacological test to confirm Horner syndrome, and what does a positive result look like?
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Apraclonidine drops — the Horner pupil dilates (and the ptosis may lift), reversing the anisocoria.
Why? Denervated dilator muscle develops hypersensitive alpha-1 receptors, so it responds to apraclonidine's weak alpha-1 effect while the normal pupil does not.
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What is the first-line investigation for an acute painful Horner syndrome with neck pain?
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Urgent CT or MR angiography of the neck to look for internal carotid artery dissection.
Why? Painful Horner is carotid dissection until proved otherwise. It is third-order, so sweating is preserved: the sweat fibres leave with the external carotid.
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Small, irregular, bilateral pupils that accommodate but do not react to light — what is the classic cause?
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Neurosyphilis (Argyll Robertson pupils).
Why? This is light–near dissociation from a pretectal (dorsal midbrain) lesion. Diabetes is another cause.
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Which bedside drug test confirms a Holmes–Adie (tonic) pupil?
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Dilute pilocarpine (0.1%) — the Adie pupil constricts, the normal pupil does not.
Why? The damaged ciliary ganglion causes denervation hypersensitivity of the sphincter. Typically a young woman with one dilated, slowly reacting pupil and reduced tendon reflexes.
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What is the most common cause of dorsal midbrain (Parinaud's) syndrome?
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A pineal tumour (pinealoma).
Why? The tumour compresses the dorsal midbrain. MRI brain is the first-line investigation.
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Name two drugs or poisons that cause pinpoint pupils.
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Opioids and organophosphates (others: pilocarpine, clonidine/apraclonidine).
Why? Opioids act on the Edinger–Westphal nucleus; organophosphates block acetylcholinesterase, causing parasympathetic overactivity.
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Name the two main drug classes that cause dilated pupils.
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Anticholinergics (atropine, tropicamide, tricyclics) and sympathomimetics (amphetamines, cocaine, MDMA).
Why? Anticholinergics paralyse the sphincter; sympathomimetics stimulate the dilator.
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Name the classic triad of Horner syndrome.
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Ptosis (partial), miosis and anhidrosis — with apparent enophthalmos.
Why? All come from loss of sympathetic supply: Müller's muscle (ptosis), pupil dilator (miosis) and facial sweat glands (anhidrosis).
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Horner syndrome with shoulder pain and wasting of the small hand muscles in a smoker suggests which tumour?
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Pancoast tumour (apical lung cancer) — a second-order (preganglionic) Horner.
Why? The tumour invades the sympathetic chain and the lower brachial plexus (C8–T1). Anhidrosis affects the face.
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Horner syndrome with ipsilateral facial numbness, contralateral loss of pain and temperature in the body and ataxia — which artery is usually blocked?
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The posterior inferior cerebellar artery or vertebral artery (lateral medullary / Wallenberg syndrome).
Why? This is a first-order (central) Horner, so anhidrosis can involve the face, arm and trunk.
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Which eye-drop test separates preganglionic from postganglionic Horner syndrome?
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Hydroxyamphetamine — a postganglionic (third-order) Horner pupil fails to dilate.
Why? Hydroxyamphetamine releases stored noradrenaline from intact postganglionic nerve endings; if the third-order neuron is damaged there is nothing to release.
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Which bedside test detects a relative afferent pupillary defect?
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The swinging light (flashlight) test — both pupils dilate when the light moves to the affected eye.
Why? An RAPD means unequal afferent input, e.g. optic neuritis or a large retinal detachment. Cataract does not cause one.
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Name the two drugs used to treat organophosphate poisoning.
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Atropine (blocks muscarinic effects) and pralidoxime (reactivates acetylcholinesterase).
Why? Organophosphates inhibit acetylcholinesterase, causing pinpoint pupils, salivation, bronchorrhoea and bradycardia. Atropine is titrated until secretions dry.
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Tropicamide dilates the pupil by ______; phenylephrine dilates it by stimulating alpha-1 receptors on the dilator pupillae.
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blocking muscarinic receptors on the sphincter pupillae
Why? Antimuscarinics also paralyse accommodation (cycloplegia); phenylephrine does not.
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Tropicamide dilates the pupil by blocking muscarinic receptors on the sphincter pupillae; phenylephrine dilates it by ______.
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stimulating alpha-1 receptors on the dilator pupillae
Why? Antimuscarinics also paralyse accommodation (cycloplegia); phenylephrine does not.
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After a head injury, a patient's GCS falls and one pupil becomes fixed and dilated. What is the likely mechanism?
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Uncal (transtentorial) herniation compressing the third nerve on the same side.
Why? The pupillary fibres lie on the outside of the nerve, so the pupil goes first. This is a neurosurgical emergency.