A 32-year-old woman presents with sudden horizontal double vision that started three days ago on waking. There was no trauma, headache, weakness or numbness. The double vision is present in all directions of gaze and does not worsen as the day goes on. She is otherwise healthy and takes no regular medication. She is frightened that she has had a stroke.
Examination Findings
Visual acuity 6/6 both eyes with current glasses. Cover test: a comitant esotropia of about 25 prism dioptres, equal at distance and near and in all directions of gaze. Extraocular movements full, no nystagmus. Pupils normal, no ptosis. Anterior segment and dilated fundus normal. Cycloplegic refraction shows mild myopia, fully corrected by her glasses. Neurological examination normal.
Investigations
MRI of the brain and orbits with contrast to exclude a central cause — reported normal. Blood tests including thyroid function normal. Myasthenia workup not indicated given the constant comitant picture, but kept in mind if the pattern changes. Prism cover testing in all gaze positions documents the comitant nature.
Questions to Think About
- Why is this presentation treated as urgent even though the eyes look almost normal at a glance?
- What single examination feature most strongly argues against a sixth nerve palsy here?
- If the MRI is normal, what are the options for the persistent double vision?
Diagnosis
Acute acquired comitant esotropia in an adult, with no neurological cause found on workup.
Reasoning
Reasoning: Sudden binocular horizontal diplopia in an adult must be assumed neurological until proven otherwise, because sixth nerve palsy, myasthenia and intracranial pathology all present this way. The key finding here is comitance — the esotropia measures the same in every gaze direction — which argues against a single-nerve palsy (those are worst in the field of the weak muscle). Normal pupils, no fatigability, full movements and a normal neurological examination further narrow the field, but imaging is still mandatory because comitant presentations of central lesions are described. Diagnosis: acute acquired comitant esotropia with a negative neurological workup. Management: typical management is neuroimaging first, then prisms for symptom control once the cause is cleared, with strabismus surgery per local protocol if the deviation persists. The patient is counselled that the normal MRI is reassuring but that any change in the pattern needs re-evaluation.
Differential Diagnosis
- Sixth nerve palsy — ruled out: the deviation is equal in all gaze directions (comitant), whereas a sixth nerve palsy is worse looking toward the affected side.
- Myasthenia gravis — ruled out: no fatigability, no ptosis, symptoms are constant rather than fluctuating through the day.
- Thyroid eye disease — ruled out: no lid signs, no proptosis, full painless eye movements, thyroid function normal.
Management
Typical management includes urgent neuroimaging first. With a normal workup, symptom relief with Fresnel or ground-in prisms while the deviation stabilises, then strabismus surgery (usually bilateral medial rectus recession) per local protocol if the diplopia persists and is bothersome. Botulinum toxin injection to the medial rectus is an option some centres use. Regular orthoptic follow-up monitors for any change in pattern.
Key Learning Points
- Sudden-onset diplopia in an adult is a red flag until a neurological cause is excluded — neuroimaging is the priority, not the squint itself.
- Comitant means the angle is the same in every gaze direction; incomitant points toward a nerve palsy or restriction.
- Once the workup is clear, acute acquired comitant esotropia is managed like other comitant strabismus: prisms for symptom relief, then surgery per local protocol.
- A normal MRI does not end follow-up — the patient is warned to return if double vision changes pattern, or if headache, weakness or numbness appears.
Red Flags
- Any new neurological symptom (headache, weakness, numbness, slurred speech) — return to emergency care immediately.
- A deviation that becomes unequal in different gaze directions — suggests a developing nerve palsy or restriction, re-examine promptly.
- Diplopia that starts fluctuating or comes with drooping lids — reconsider myasthenia.
Educational content only — not medical advice. Clinical decisions must be made by a qualified professional for the individual patient.