Neuro-Ophthalmic
Microvascular Cranial Nerve Palsy
Also known as: microvascular CN palsy, diabetic CN palsy, single-nerve CN VI palsy, single-nerve CN IV palsy, abducens palsy microvascular, trochlear palsy vasculopathic, pupil-sparing CN III, lateral rectus palsy diabetes
Filed as: Urgent
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
An isolated third, fourth or sixth nerve palsy from small-vessel ischaemia, typically in an older patient with diabetes or hypertension, causing sudden double vision that may be preceded by an ache. The deficit follows one nerve and the pupil is spared. Pupil involvement, more than one nerve affected, a young patient, or no vascular risk factors at any age each move the case out of this pattern and into urgent investigation.
Recognition
Symptoms: what patients report
- Sudden onset of binocular horizontal or vertical diplopia.
- Diplopia resolves with one eye covered — supporting binocular origin.
- Mild periorbital or retro-orbital aching pain may be present at onset (especially CN IV).
- A droopy lid is expected in a third nerve palsy; a dilated or poorly reactive pupil is not — pupil involvement points to a compressive CN III palsy.
- Symptoms typically stable after onset — progressive worsening is a red flag.
Signs: what the examination shows
- Single-nerve limitation of ocular movement corresponding to the affected muscle.
- CN VI: esotropia in primary gaze, failure of abduction — lateral rectus weakness.
- CN IV: hyper-deviation with head tilt, worsening on contralateral gaze — superior oblique weakness.
- Pupils equal and reactive. In a third nerve palsy a spared pupil makes compression less likely but does not exclude it — pupil-sparing aneurysmal and compressive palsies are documented, and mild pupil involvement can occur in a microvascular palsy. Every acute third nerve palsy is imaged.
- CN III: ptosis (often complete) and ophthalmoplegia are expected in a microvascular third nerve palsy; neither the lid nor a spared pupil distinguishes it from a compressive palsy, and a dilated pupil raises the concern further. CN VI and CN IV palsies have no ptosis.
- No proptosis, no orbital signs.
What OptoGuide™ covers for microvascular cranial nerve palsy
- Pattern reasoning: what this combination of findings points to, and its differentiators
- Don't-miss risks and escalation triggers
- Management tiers with linked Australian therapeutics
- Referral urgency, specialty, and letter drafting
Sources
- Microvascular Cranial Nerve Palsy — NANOS
- The Neuro-Ophthalmology Survival Guide (Pane, Miller & Burdon) — standard reference text
- Intracranial aneurysm risk stratification in acute ocular motor nerve palsy based on clinical features. Ding Y, Ding X, Huang B. Scientific Reports. 2025;15(1):36871.
- Isolated Third, Fourth, and Sixth Cranial Nerve Palsies From Presumed Microvascular Versus Other Causes: A Prospective Study. Tamhankar MA, Biousse V, Ying GS, et al. Ophthalmology. 2013;120(11):2264-9.
- The spectrum and differential diagnosis of acquired ocular motor nerve palsies: a clinical study of 502 patients. Hörner R, Kassubek J, Dreyhaupt J, Ludolph AC. Journal of Neurology. 2022;269(4):2140-2148.
- Incidence and Etiologies of Acquired Third Nerve Palsy Using a Population-Based Method. Fang C, Leavitt JA, Hodge DO, et al. JAMA Ophthalmology. 2017;135(1):23-28.
- Adult Strabismus Preferred Practice Pattern. Dagi LR, Velez FG, Holmes JM, et al. Ophthalmology. 2024;131(4):P306-P403.
- British Society for Rheumatology guideline on diagnosis and treatment of giant cell arteritis: executive summary. Mackie SL, Dejaco C, Appenzeller S, et al. Rheumatology (Oxford). 2020;59(3):487-494.
Standard texts: Kanski's Clinical Ophthalmology: A Systematic Approach, Oxford Handbook of Ophthalmology, Oxford American Handbook of Ophthalmology, Signs in Ophthalmology: Causes & Differential Diagnosis.