DON’T FORGET THE DOUBLE VISION (Diplopia rapid review)


This is a guest post by Kristine Laing, CCPA. Kristine is Canadian Certified Physician Assistant working in emergency medicine in Toronto.  She is also a facilitator for the University of Toronto Physician Assistant Program and is part of the faculty for Dr. Arun Sayal’s incredible Casted Course. 

Cite this article as:
Laing, K. DON’T FORGET THE DOUBLE VISION (Diplopia rapid review), First10EM, September 27, 2021. Available at:

Cathy awoke in the morning with what she described as double vision. She got a quick appointment with her optometrist who then sent her to the ED for a further workup. By the time I saw Cathy, her diplopia had resolved and she felt completely normal. She wondered if she should just go home and felt silly for being in the ED.

Diplopia, or double vision, can be a tricky and complicated disorder. There are various forms of double vision and many etiologies, ranging from non-serious to life-threatening. I always felt a little confused and unsure of how to approach someone with Diplopia.  So here goes my step-wise approach to optimize the care of a patient with non-traumatic diplopia.

Step 1: Is this Monocular or Binocular?

This is the most important initial question, as it distinguishes whether the problem stems from the brain or the eye. 

Monocular diplopia is almost always eye related and not life-threatening.  Binocular diplopia is brain-related and should therefore raise some alarms. Monocular diplopia is when a patient’s double vision affects one eye. (The double vision remains even when one eye is covered or closed.) On the other hand, binocular diplopia occurs with both eyes open and resolves when one eye is covered or closed. 

Monocular diplopia is typically a refraction or functional issue of the eye and no further ED imaging is required. It accounts for approximately 15% of diplopia cases. Arrange rapid follow-up with ophthalmology rather than neurology.

Binocular diplopia (85% of diplopia presentations) is a cranial nerve or brain issue that requires further workup in the ED. 

Step 2:  Isolated binocular diplopia – or are there other neurological symptoms? 

Consider stroke if there is acute binocular diplopia plus any other neurological signs or symptoms, such as vertigo, aphasia, ataxia, dysphagia, ipsilateral cranial motor deficits or contralateral sensory or motor weakness.  Proceed with your ED’s stroke protocol.

Step 3:  Isolated binocular diplopia – is this cranial nerve 3 or not?

An acute CN3 palsy is an aneurysm or ruptured aneurysm until proven otherwise.  If the patient has isolated diplopia, rule out CN3 involvement. CN4 or CN6 isolated palsies are typically less urgent.  

If you are like me, you will need a quick reminder of the function of these three cranial nerves. I use the mnemonic “SO4LR6 everything else CN3”.

  • Cranial Nerve 4: Trochlear nerve innervates the superior oblique muscle moving the eye down and inwards (depression and intorsion)
  • Cranial Nerve 6: Abducens nerve innervates the lateral rectus muscle, abducting the eye outwards and away from the nose
  • Cranial Nerve 3: The Oculomotor nerve innervates the rest of the oculomotor muscles as well as the levator palpebrae superioris (the upper eyelid). It also controls the parasympathetic action of constricting the pupil 

Very thorough extraocular testing is a must. Ensure the patient’s head is stationary, facing forward, and does not move.  With only their eyes, have them follow your finger quickly in all the different cardinal positions of gaze (if you move too slowly they can compensate for their deficit). 

CN PalsySigns/SymptomsCommon Causes You Don’t Want to MissInvestigations/Referrals
CN 3– Pupil is ‘down and out’
– Can have multi-directional, horizontal or vertical diplopia. 
– There may be ptosis and +/- pupillary dilation
Pearl: Ptosis with normal pupillary dilation is likely not a serious cause
– Aneurysm or compression lesion
Fun fact: the most common life-threatening aneurysm is found at the junction of the posterior communicating artery and carotid artery, where CN3 runs just below.  At 4-5mm the aneurysm begins to compress CN3 thus causing the palsy
– Urgent CTA head to rule out aneurysm or compressive lesion
– Appropriate referral based on imaging findings
CN 4 – Often vertical diplopia
– An affected person may chin tuck and/or tilt head sideways to balance the pupils to correct the diplopia
– Can be very tricky to diagnose but typically not sinister 
– Usually not ominous:
Microangiopathic disease
– If confident this is a non-traumatic isolated CN 4 palsy, refer to Ophthalmology.
– Urgent imaging is not necessary
CN 6 – Most common isolated ocular nerve palsy
– Typically a horizontal diplopia, as the affected eye drifts medially relative to the normal eye
– An affected person will turn their head sideways to align their eyes
– In elderly, consider microangiopathic disease
– Cerebral Venous Thrombosis
Idiopathic Intracranial hypertension
– Bilateral palsy = bad: consider intracranial or subdural bleeds, neoplasm at the clivus, brainstem infarction
– Fundoscopic exam or urgent Ophthalmology referral to rule out papilledema
– CT venogram to rule out CVT if this is the top differential
– Bilateral palsy; do thorough workup

Step 4: Are there multiple extraocular nerve palsies? 

If more than one extraocular nerve is involved, the lesion is probably where the ocular cranial nerves run close together, such as the the orbital apex (most posterior area of the orbit) and the cavernous sinus (paired sinuses sandwiching the pituitary fossa at the skull base). 

Orbital apex: The trigeminal nerve and optic nerve (cranial nerve 2) also travel through this region.  In orbital apex syndrome (OAS), multiple extraocular nerve palsies will be paired with a trigeminal nerve palsy and vision loss. Inflammation, infection, trauma, and neoplasm can cause OAS. Consider an urgent CT scan of the orbits with the rest of your workup.

Cavernous sinus: The trigeminal nerve, the carotid artery, and the sympathetic nerves also travel through this sinus.  Unlike the Orbital apex, it does not contain the optic nerve therefore should not involve vision loss. Like OAS, inflammation, infection, trauma, and neoplasm can occur within the cavernous sinus. It is important to consider septic cavernous sinus thrombosis (CST) with any toxic-appearing patient.

Step 5: Consider other causes if diplopia is still unexplained.

Giant Cell Arteritis: In patients 60 years or older, assess for GCA with CBC, ESR and CRP.  (Consider GCA even if the diplopia is transient with no other symptoms.)

Myasthenia Gravis:  In a patient with fluctuating diplopia with or without ptosis, consider MG. If possible, add acetylcholine receptor antibody with the bloodwork, as it can take several weeks for results, and the diagnosis can therefore be delayed if the test is not done in the ED. (This test can be very expensive. It makes sense to discuss the clinical findings with a neurologist before it is sent.)

An ice-pack test is an easy physical exam test to help confirm MG. Obtain an ice pack and apply to the affected eye for approximately 2 minutes making sure you prevent an ice burn. In MG, the ptosis should improve.  

Thyroid Ophthalmopathy: Thyroid eye disease is an autoimmune disorder typically related to  Grave’s disease.  Patients with thyroid eye disease may have symptoms such as eye dryness, photophobia, or pressure behind the eyes with or without diplopia.  You may be able to see proptosis, extraocular deficiencies, conjunctivitis and eyelid edema. Obtain TSH, T4 and consider urgent MRI with orbit views.  

Wrap Up

Back to my patient, Cathy.  On exam, Cathy had normal ocular movements. Her pupils were slow to dilate. She had a subtle anisocoria that she denied being aware of before. Her diplopia had resolved, but her description was clearly of binocular diplopia. We proceeded with bloodwork and a CT angiogram of the head and neck, as her presentation was most in keeping with a CN3 palsy. To our surprise, Cathy had a pseudoaneurysm of the left vertebral artery most in keeping with a dissection, and is now being followed by neurology.

Diplopia can be a clue to many different conditions ranging from benign to very serious and life-threatening conditions. I hope this article helps clarify and organize an approach to diplopia to optimize your patient’s care while in the emergency department. 


Margolin Edward, Lam TY Cindy. Approach to a Patient with Diplopia in the Emergency Department. The Journal of Emergency Medicine, 2018 June 01: Vol 54, Issue 6, pp 799-806.

Dinkin, Marc. Diagnostic Approach to Diplopia. Continuum American Academy of Neurology, 2014 August: Vol 20, Issue 4, pp 942–965.

Iliescu D, Timaru C, Alexe N, Gosav E, De Simone A, Batras M,Stefan C. Management of diplopia. Romanian Journal of Ophthalmology, 2017 Jul-Sep: Vol 61 Issue 3, pp 166–170.

Many thanks to Neurologist Dr. Hamza from Markham Stouffville Hospital who I reached out to for advice and who provided helpful insight on how to simplify the treatment of diplopia in the Emergency Department. 

Cite this article as:
Laing, K. DON’T FORGET THE DOUBLE VISION (Diplopia rapid review), First10EM, September 27, 2021. Available at:

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