Diplopia and cranial nerve palsy

Pertinent questions when taking the history

• How long has the double vision been present? Did it begin all of a sudden, or was the onset slower?
• Has the separation between the two images increased, decreased, or stayed the same since the symptoms began?
• Does the double vision resolve when either eye is covered? This separates monocular double vision, seen with a single eye, from binocular double vision, present only when both eyes are open.
• Has there been any recent trauma? Head and orbital injuries can damage these nerves directly, and an orbital fracture can trap an eye muscle.
• Has there been pain around the eye, or a headache, along with the double vision?
• Is the patient a vasculopath, with diabetes, high blood pressure, kidney disease, or heart disease? These patients have a higher risk of ischemic cranial nerve palsies, which are often accompanied by a low grade headache and tend to improve over weeks to a few months. Vascular risk factors do not prove a palsy is ischemic.

Visual vital signs

Vision, pressure, and pupils, recorded and handed off like any other vital sign. Vision and pressure are typically normal in an isolated ocular motor nerve palsy, so an abnormal value redirects the workup. Examine the pupils carefully: a third nerve palsy can make one pupil larger or slow to constrict.

An isolated ocular motor nerve palsy does not cause an afferent pupillary defect. An afferent defect points to optic nerve dysfunction or marked asymmetric retinal disease. Together with an eye movement palsy, consider an orbital apex process, and after trauma an optic nerve injury.

Monocular or binocular

• BinocularAsk the patient to cover one eye. If the second image disappears as either eye is covered, the patient has binocular double vision, which suggests an eye movement problem and a possible cranial nerve palsy.
• MonocularIf two images persist in the uncovered eye, the double vision is monocular. This is often seen when the glasses prescription needs to change or the ocular surface is irregular. Perform a pinhole test: a pinhole typically improves or eliminates monocular double vision when the cause is optical, such as a needed change in glasses, dry eye, or another disruption of the ocular surface. Pinhole test video

Describe the focused anatomy

Describe the lids, the orbit, and the eye movements, then match the pattern to a nerve.

• Upper eyelidsIs there ptosis, an abnormal drooping of the lid on one or both sides? Ptosis may suggest third nerve involvement or other orbital disease limiting lid function. With a third nerve pattern it raises concern for an aneurysm, because every new third nerve palsy needs vascular imaging.
• OrbitIs there fullness, swelling, congestion, or enlargement of the tissues around the eye? Has one or both eyes begun to protrude, turn red, or feel tender to the touch? These suggest orbital disease or infection.
• Eye movementsDoes either eye fail to move completely in any direction? The patient may report the double vision in a particular direction of gaze during this part of the exam, which tells you whether it is horizontal, vertical, or present in several directions.

Which nerve

• Third nerveEyelid droop, with the eye deviated down and out. The pupil may be dilated.
• Fourth nerveVertical double vision, worse looking down, as when reading or on stairs. The patient tilts the head toward the opposite shoulder to reduce it.
• Sixth nerveThe eye turns in and cannot move outward. Horizontal double vision, worse at distance and when looking toward the affected side. The patient turns the face toward the affected side to reduce it.
• More than one nerveA red flag. See below.

Supporting imaging, if needed

• Vascular imaging for a new third nerve palsyUrgent CTA or MRA of the head to look for an intracranial aneurysm, adding the neck when clinically indicated. Suspicion is higher when binocular double vision comes with a pupil abnormality, eyelid ptosis, or both. The choice depends on availability, patient factors, and local neuroradiology expertise; in the emergency department CTA is often the fastest. Write "third nerve palsy, rule out posterior communicating artery aneurysm" on the order and ask for a neuroradiology read, since missed aneurysms are usually visible on the scan.Source: Margolin 2018; Kupersmith 2006; Elmalem 2011
• MRI brain with and without contrastAdd orbital and cavernous sinus sequences when the localization suggests them, and a demyelination protocol only when the history or examination raises that concern. MRI is the preferred test for ocular motor palsies in general, and may be recommended for a younger patient, when systemic symptoms are present, or when the examination shows atypical findings.Source: Margolin 2018
• Any new third nerve palsyNeeds vascular imaging before discharge, including a partial palsy, one with ptosis, or one with a normal pupil. A normal pupil lowers the odds of an aneurysm but does not rule it out.Source: Jacobson 2001; Kissel 1983; Margolin 2018
• Isolated fourth or sixth nerve palsyIn an older patient with established vascular risk factors and an otherwise normal neurologic examination, close observation without immediate MRI is an accepted approach in some practices. Early MRI is also reasonable, because important other causes turn up even in vasculopathic patients. Image promptly if the presentation is atypical, progresses, gains new neurologic signs, or fails to improve by about three months.Source: Tamhankar 2013; Yao 2026, which notes that the best timing of imaging remains controversial

Treatment

• Emergencies firstArrange emergent evaluation and treatment for any suspected intracranial aneurysm or orbital disease.
• Relief of double visionIn non urgent cases, occlude the vision in one eye for symptomatic support until ophthalmology can perform a more detailed evaluation.
• HeadacheManage with appropriate analgesics.
• Vascular risk factorsCheck the blood pressure and review diabetes and lipid status; obtain glucose or hemoglobin A1c when diabetes status or control is unknown. Other laboratory tests should follow the clinical picture. Encourage correction of systemic abnormalities where able.Source: Jung 2015, where diabetes, hypertension, and hyperlipidemia were the leading risk factors
• Age 50 or olderScreen for giant cell arteritis: ask about headache, jaw pain on chewing, scalp tenderness, and brief episodes of vision loss, and check ESR and CRP. A CBC with platelet count is often added. Arteritis can present with double vision alone; in one prospective series, all three such patients had a sixth nerve palsy.Source: Tamhankar 2013; Ross 2019
• What ophthalmology may add laterA temporary prism over the deviating eye's spectacle lens, prism built into glasses for more permanent deviations, additional neuroimaging in atypical cases, or eye muscle surgery to realign the eyes.

Follow up

• New third nerve palsy, especially pupil involvingAn emergency evaluation, not a follow up visit. Obtain emergency vascular imaging, with immediate neurovascular or neurosurgical evaluation if an aneurysm is found or strongly suspected. Ophthalmology or neuro-ophthalmology follow up comes after the emergency evaluation.
• Isolated fourth or sixth nerve palsyOphthalmology follow up within three to five days to evaluate for further therapy. Tell the patient to return at once for a droopy lid, a larger pupil, worsening headache, new weakness or numbness, or vision loss.
• Third nerve palsy with a normal pupilNot cleared by the pupil alone. It needs vascular imaging first, because the pupil can become involved within days.
• Systemic follow upArrange primary care or other systemic follow up if uncontrolled vascular conditions are present.
• Expected courseIschemic palsies usually begin improving within several weeks; average recovery in one series was 6 to 9 weeks, and most resolve by three to six months. No clear improvement by about three months, progression, or new findings should prompt reconsideration of the diagnosis and neuroimaging if not already done. Double vision that persists may be due to a decompensated phoria, a long standing tendency of the eyes to drift that the eye muscles can no longer hold in check. Atypical double vision may warrant neurologic consultation or systemic evaluation.Source: Jung 2015; Yao 2026
• Your job at the point of careRule out the emergencies: a pupil involving palsy, orbital tumor, orbital cellulitis, stroke, encephalitis, or a neuroinflammatory condition. Once those are excluded, outpatient follow up can lead to a more detailed diagnosis and treatment plan.