Neuro-Ophthalmic
Physiologic Anisocoria
Also known as: physiologic anisocoria, physiological anisocoria, benign anisocoria, longstanding anisocoria, old photos anisocoria
Filed as: Routine
Source-cited from the record's own evidence list. Clinical content programme led by Dr Ankit Mathur, PhD, Grad Cert Ocu Thera, B.S. Optom. How the clinical content is governed
Clinical decision support only
Overview
A benign difference in pupil size, usually under a millimetre, present in a substantial minority of people and stable across years. The difference stays similar or slightly larger in dim light, with no dilation lag, both pupils react normally, and old photographs typically show the same pattern. That stability, and the symmetry of the light reaction, are what distinguish it from a newly acquired difference, which is assessed rather than assumed benign.
Recognition
Symptoms: what patients report
- Usually asymptomatic incidental anisocoria.
- Longstanding history or old photos showing the same pattern.
Signs: what the examination shows
- Typically less than 1 mm difference.
- Stable across time.
- Often slightly larger in dim light, as a Horner pupil is, so light versus dark alone does not separate them.
- Normal iris appearance.
- No ptosis, diplopia, motility restriction, pain, red eye, or neurological features.
What OptoGuide™ covers for physiologic anisocoria
- Pattern reasoning: what this combination of findings points to, and its differentiators
- Don't-miss risks and escalation triggers
- Management tiers with linked New Zealand therapeutics
- Referral urgency, specialty, and letter drafting
Sources
- Abnormalities of the pupil — College of Optometrists Clinical Management Guideline
- The Neuro-Ophthalmology Survival Guide (Pane, Miller & Burdon) — standard reference text
- Pearls & Oy-Sters: Anisocoria Greater in the Dark: It's Not Just All About Horner Pupil. Witsberger E, Mansukhani SA, Chen JJ, Bhatti MT. Neurology. 2021;96(15):719-722.
- Unilateral mydriasis: an unexpected effect of ipratropium bromide inhalation—a brief report. Levy B, Ziv N, Krause I. European Journal of Pediatrics. 2025;184(4):239.
- The Eye in Neurological Disease. Miller NR, Newman NJ. Lancet (London, England). 2004 Dec 4-10;364(9450):2045-54.
- Differentiation of Horner Syndrome and Physiological Anisocoria by Automated Pupillometry. Disse LR, Bockisch CJ, Weber KP, Fierz FC. J Neuroophthalmol. 2025;45(3):327-332.
- The prevalence of simple anisocoria. Lam BL, Thompson HS, Corbett JJ. Am J Ophthalmol. 1987;104(1):69-73.
Standard texts: Kanski's Clinical Ophthalmology: A Systematic Approach, Oxford Handbook of Ophthalmology, Oxford American Handbook of Ophthalmology, Signs in Ophthalmology: Causes & Differential Diagnosis.