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, or an age over 50 without a vascular explanation 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).
- No ptosis or pupil involvement (distinguishes from CN III compressive 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, round, and reactive — pupil sparing is critical in CN III.
- No ptosis (CN VI or IV palsies); no significant ptosis in pupil-sparing CN III.
- 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
Standard texts: Kanski's Clinical Ophthalmology: A Systematic Approach, Oxford Handbook of Ophthalmology, Oxford American Handbook of Ophthalmology, Signs in Ophthalmology: Causes & Differential Diagnosis.