A 28-year-old woman notices in photographs that her right pupil is larger than her left. It is more obvious in bright light. She has no drooping lid, no double vision, and her vision is 6/6. She feels entirely well and is worried she has had a stroke.
Examination Findings
Anisocoria: right pupil 6 mm, left 3 mm in bright light; the difference is less in dim light (worse in light). The right pupil reacts sluggishly to light but constricts better — slowly and tonically — to a near target (light-near dissociation). Segmental iris constriction is visible on slit lamp. Extraocular movements full, no ptosis, discs healthy. Deep tendon reflexes are reduced. Dilute pilocarpine testing constricts the affected pupil, confirming denervation supersensitivity.
Investigations
Dilute pilocarpine testing confirms the tonic pupil. No neuroimaging is needed for an isolated classic Adie’s pupil with no other signs. Reflexes are checked as part of the Holmes-Adie picture.
Questions to Think About
- Why is the anisocoria worse in bright light?
- What is light-near dissociation telling us?
- When does anisocoria need urgent imaging instead?
Diagnosis
Adie’s tonic pupil (Holmes-Adie syndrome), right eye — benign postganglionic parasympathetic denervation.
Reasoning
Reasoning: Adie’s tonic pupil is parasympathetic denervation of the iris sphincter and ciliary muscle — the pupil cannot constrict to light briskly, so in bright light it stays large while the normal pupil constricts, making the difference obvious; in dim light both are large and the difference shrinks. The near response survives better than the light response (light-near dissociation) because near fibres regenerate aberrantly after the injury — the classic tonic, slow constriction. Reduced reflexes complete the Holmes-Adie syndrome. Diagnosis: Adie’s tonic pupil (Holmes-Adie syndrome), right eye — benign. Management: typical management includes reassurance — no treatment is needed for the pupil itself. She is told this is not a stroke, not dangerous, and often slowly improves over years; reading glasses may help if accommodation is affected, and she should return if new symptoms (ptosis, diplopia, headache) appear, since those would change the assessment entirely.
Differential Diagnosis
- Third nerve palsy — ruled out: no ptosis, movements full, pupil abnormality isolated with tonic near response.
- Pharmacologic mydriasis — ruled out: the pupil reacts (tonically) and dilute pilocarpine constricts it, proving denervation not blockade.
- Horner’s syndrome — ruled out: the abnormal pupil is the larger one, and the difference is worse in light.
Management
Typical management is reassurance and observation; no imaging or treatment is required for a classic isolated Adie’s pupil. If accommodation symptoms bother her, a weak reading addition helps. Follow-up is only needed if new neurological or ocular motor symptoms develop.
Key Learning Points
- Adie’s: anisocoria worse in LIGHT (parasympathetic failure); Horner’s: worse in DARK (sympathetic failure).
- Light-near dissociation with a slow tonic near constriction is the hallmark.
- Dilute pilocarpine constricts a denervated pupil — the confirmatory test.
- An isolated Adie’s pupil is benign and needs no scan — but new associated signs change everything.
Red Flags
- Anisocoria with ptosis or limited eye movements — third nerve palsy; urgent imaging.
- A new dilated pupil with headache — posterior communicating artery aneurysm until proven otherwise.
- Bilateral tonic pupils with areflexia and ataxia — wider neuropathy; investigate.
Educational content only — not medical advice. Clinical decisions must be made by a qualified professional for the individual patient.
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