A 28-year-old woman presents with sudden onset horizontal diplopia and right exotropia of 30 PD. On examination, she has normal visual acuity, normal pupillary responses, and no ptosis. Ocular motility testing reveals restriction of adduction of the right eye. Systemic examination is unremarkable. What is the most appropriate next step in management?

Explanation

## Clinical Context This patient presents with acute-onset exotropia with restricted adduction of the right eye — a red flag for acquired strabismus in an adult. The restriction of adduction suggests a possible sixth nerve (abducens) palsy, which is a neurological emergency until proven otherwise. ## Why Neuroimaging Is Mandatory **Key Point:** Acute-onset strabismus in an adult with restricted ocular motility is acquired strabismus until proven otherwise. Sixth nerve palsy can be the presenting sign of serious intracranial pathology (stroke, tumor, aneurysm, increased intracranial pressure). **Warning:** Do NOT assume this is a simple refractive or orthoptic problem. The restriction of adduction is the critical finding that mandates urgent neurological investigation. ## Differential Diagnosis of Restricted Adduction with Exotropia | Cause | Key Features | Imaging | Urgency | |-------|--------------|---------|----------| | Sixth nerve palsy (idiopathic or secondary) | Restricted abduction (not adduction), but ipsilateral eye drifts out | MRI brain, consider vascular risk factors | Urgent | | Medial rectus palsy (CN III branch) | Restricted adduction, may have ptosis or mydriasis | MRI orbit and brain | Urgent | | Thyroid eye disease | Bilateral, progressive, exophthalmos, lid retraction | CT/MRI orbit, thyroid function | Semi-urgent | | Orbital mass or inflammation | Restricted adduction, pain, proptosis | MRI orbit | Urgent | **Clinical Pearl:** The restriction of adduction (not abduction) in this case is unusual for sixth nerve palsy but suggests medial rectus involvement or orbital pathology. MRI is essential to differentiate. ## Management Algorithm for Acute Adult Strabismus ```mermaid flowchart TD A[Adult with acute strabismus + restricted motility]:::outcome --> B{Neurological signs?}:::decision B -->|Yes or unclear| C[MRI brain and orbits]:::action C --> D{Pathology found?}:::decision D -->|Yes| E[Treat underlying cause]:::action D -->|No| F[Reassess in 4–6 weeks]:::action F --> G{Spontaneous recovery?}:::decision G -->|Yes| H[Observation, prisms if needed]:::action G -->|No| I[Consider surgery after 6–12 months]:::action ``` **High-Yield:** In adults, acquired strabismus with ocular motility restriction requires neuroimaging before any orthoptic or surgical intervention. Idiopathic sixth nerve palsy may recover spontaneously over 3–6 months, but imaging must exclude serious causes first. ## Why Other Options Are Premature - **Prism glasses and exercises:** Appropriate only after neurological cause is excluded and if the deviation is stable. - **Surgery:** Never performed acutely; wait 6–12 months for spontaneous recovery in nerve palsies. - **Cycloplegic refraction:** Irrelevant when there is restricted motility; refraction does not explain mechanical restriction. [cite:Strabismus and Neuro-ophthalmology, AIIMS teaching material; Harrison 21e Ch 428]