Diagnosing the cause of new onset diplopia can be daunting. It can be doubly challenging if you are not familiar with or have forgotten common causes of it.
This flowchart serves to re-acquaint you with common causes of diplopia and help streamline your clinical thought process and decision making when presented with unexpected double vision in the exam room.
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Please note that this chart serves merely as a guide for common diagnoses associated with the symptoms of diplopia that are mentioned. As with many cases in medicine, a diagnosis does not always fit into a “box”. Many conditions present with atypical symptoms and many symptoms are associated with more than one or an atypical diagnosis. When using this guide, be sure to use your best clinical judgment on a case-by-case basis.
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Start with a thorough clinical history
Correctly diagnosing diplopia always starts with taking a good clinical history. Be sure to determine that the patient has true diplopia and not a masquerader such as ghosting or blurry vision. Once you have determined they are in fact presenting with diplopia, the best initial question to ask is “Does the double vision go away when you cover one eye?” If the answer is no, then they have a monocular cause of diplopia. If the patient has diplopia regardless of the eye they cover, they may have a cortical issue or bilateral issues causing monocular diplopia. If symptoms are relieved by covering a specific eye, that is the eye causing the diplopic issues.
Note that a patient can always present with both binocular and monocular causes of double vision. While most of the time if a patient has both monocular and binocular (or cortical) issues they will experience polyopia (more than two images), they may be poor historians or have difficulty articulating their complaint. If diplopia is not relieved by covering one eye, we cannot assume that a monocular cause is the only cause.1-3,9
Binocular versus monocular diplopia
Once the diplopia is determined to be monocular, we can narrow our list of potential diagnoses with pinhole testing. If there is improvement in the diplopia with pinhole, common monocular causes of diplopia include ocular surface disease (OSD), corneal opacity or irregularity (such as keratoconus), cataract or lens displacement (natural or implant), refractive error (including anisometropia), spectacle misalignment, iris defects (such as iridodialysis, polycoria, or iridotomy), or vitreous opacities.1 If there is no improvement of monocular diplopia through pinhole, common causes of monocular diplopia include retinal detachment, macular pathology, and cortical abnormalities (such as visual cortex lesions, Parkinson’s disease, or migraine).1-4
If a patient covers one eye, and the double vision resolves, they are experiencing binocular double vision. Once you determine a patient is experiencing binocular diplopia, the most pertinent initial question to ask is in what direction(s) are the two images displaced: Are they horizontally displaced, vertically displaced, or diagonally/obliquely displaced? Remember, diagonal displacement may mean a torsional component or both horizontal and vertical components to the diplopia.
Horizontal diplopia
If the double vision the patient is experiencing presents with images side by side, we then want to ask when the diplopia is seen: Is it worse in any particular direction or distance? Horizontal diplopia is typically caused by an issue with the lateral or medial recti muscles. If the diplopia is worse or present only at distance, the most likely causes are a cranial nerve VIth palsy or divergence insufficiency. If the horizontal image separation is worse at near or only occurs after prolonged near work, the more likely causes are convergence insufficiency or a decompensated phoria.4,5 Note that convergence insufficiency often occurs in patients with Parkinson’s disease.4
Horizontal diplopia may also only be present or may be worse when looking in either left or right gaze. If this is the case, we must determine if there is a physical limitation on forced duction testing. If there is, consider muscle paresis, an orbital lesion, or thyroid eye disease as the cause.
If muscle paresis is the cause of diplopia, the diplopia will be exacerbated in the direction of the impaired muscle. Conversely, if there is muscle enlargement from thyroid eye disease, the diplopia will likely be worse in the opposite direction of the affected muscle. Remember that thyroid eye disease can present with these issues in vertical gaze as well, as it can impact any of the extraocular muscles, particularly the inferior recti.4
Diplopia caused by an orbital lesion is likely to be more slow in onset and the restrictive nature depends on where the lesion is located.4,5,13 Orbital lesions include masses, inflammation, and trauma. These have the potential to be an ocular emergency. 13 Note that trauma can cause an orbital blowout fracture, which in turn may result in muscle entrapment. While a blowout fracture can impact any area of the orbit, it most often occurs inferiorly and entraps the inferior recti, which causes vertical diplopia.6
For horizontal diplopia that is worse in either left or right gaze but does not necessarily have limitation on forced duction testing, consider a VIth nerve palsy, Myasthenia Gravis (MG), or an internuclear ophthalmoplegia (INO) often from Multiple Sclerosis (MS). The most common causes of horizontal diplopia are VIth nerve palsy and internuclear ophthalmoparesis (INO).4 Remember that an INO results from a lesion in the MLF, and is marked by complete or partial inability to adduct the ipsilateral eye and nystagmus in abducting eye. It can be unilateral or bilateral.4,7
Myasthenia Gravis (MG) is a chronic autoimmune disease affecting the neuromuscular junction that often presents with diplopia.4 Diplopia from MG may present as worse in left or right gaze, but may also not necessarily have a consistent pattern. Any of the extraocular muscles can be affected, thus double vision can occur horizontally, vertically, or diagonally. The diplopia can be intermittent and variable, but often occurs more notably at the end of the day. Patients may also present with unilateral or bilateral ptosis, fatigue, and muscle weakness.4,5
Other causes of intermittent diplopia are decompensated phoria or existing intermittent phoria/strabismus.4,5 Ask your patient if they had any correction for childhood strabismus. Typically, patients that have a congenital constant strabismus that was not surgically corrected do not experience diplopia due to cortical suppression from childhood. However, if they had surgical correction or if the strabismus was intermittent, it is likely that they are experiencing a decompensated phoria.5 These deviations are generally comitant.4 If diplopia does not follow a consistent pattern, fluctuates, or the patient is uncertain of the direction, further workup is required. Ask your patient about other associated symptoms and consider cover tests in multiple gazes as well as Maddox rod testing. The implications of these findings are detailed below.
Vertical or diagonal diplopia
Moving on to vertical or diagonal diplopia, we require further investigation. If a patient presents with diagonal diplopia, and has a head tilt that relieves their symptoms, there is likely a torsional component and you should consider a skew deviation or CN IV palsy. However, these conditions do not always present with a head tilt.5
If there is no head tilt and there are no obvious associated ocular symptoms with the diplopia, cover test and Maddox rod testing can be useful in pointing you in the direction of a diagnosis. Cover test in multiple gazes can be used to check for comitancy and Maddox rod testing is useful in determining if there is a torsional component to diplopia. If findings are not consistent with a CN palsy or skew deviation, consider MG as a differential.4,5
If cover testing and Maddox rod tests are consistent with a cranial nerve palsy, you may notice the following:
- CN IV Palsy: Vertical, diagonal, or torsional diplopia worse in downgaze. With an impaired superior oblique muscle, the affected side will have a hyper deviation worse in contralateral gaze and ipsilateral head tilt. Therefore, these patients often present with a contralateral head tilt to relieve diplopia (both with congenital and acquired IV palsy). Major causes of CN IV palsy include: trauma, cavernous sinus lesion, subarachnoid space infection or inflammation, vasculopathy, and midbrain lesion.4,5
- CN III Palsy: *This is a potential ocular emergency. A CN III palsy has the potential to impair the superior rectus, inferior rectus, medial rectus, inferior oblique, or superior levator muscles. Since the affected eye cannot look up, down, or in, a reversing hyper deviation that is worse with ipsilateral head tilt and contralateral gaze will be present. In a complete cranial nerve 3 palsy, there will be ptosis and the ipsilateral eye will be positioned downward and outward.
The pupil can be used as a guide only with a complete CN 3 palsy: if the pupil is dilated with a complete palsy, this is likely an aneurysm and needs a referral for imaging and treatment to the ER immediately. If the pupil is spared in a complete CN 3 palsy, it is likely due to vasculopathic factors. If the CN III palsy is incomplete, you cannot use the pupil as a guide and must treat it as an aneurysm until proven otherwise.
If you are uncertain in any case, always refer for immediate imaging and treatment. Be sure to ask patients about vasculopathic risk factors such as diabetes, hypertension, and atherosclerosis. Major causes of CN III palsy include: cavernous sinus lesion, subarachnoid space infection or inflammation, vasculopathy, midbrain lesion, and of course aneurysm.4,5
- CN VI Palsy: As mentioned, this palsy impairs the lateral rectus, causing an eso deviation on the affected side. The eso deviation will be greatest in ipsilateral gaze. The horizontal diplopia is typically greater at a distance.4,5 Be sure to rule out papilledema, MG, and Duane retraction syndrome in all cases of suspected CN VI palsy.4,5,8 Major causes of CN VI Palsy include: trauma, cavernous sinus lesion, subarachnoid space infection or inflammation, vasculopathy, and pons lesion.5
Concurrent symptoms: when to be on alert for emergencies
When attempting to assess causes of vertical or diagonal diplopia, it will behoove you to assess the patient for concurrent ocular or facial symptoms. If the patient presents with either unilateral or bilateral proptosis or limitation on forced duction testing, consider thyroid eye disease or an orbital lesion. Note that these conditions do not always present with proptosis.4,5
If a patient presents with ptosis, consider a cranial nerve III palsy as discussed, but also consider MG, a concurrent Horner's syndrome, GCA, or stroke.
A painful CN III palsy, painful Horner's syndrome, GCA, and stroke are neuro-ophthalmic emergencies.
In honing your diagnoses, always assess the patient for facial or neck pain. All of these conditions have the potential to cause variable upper body pain, most notably a CN III palsy from an aneurysm, a Horner's syndrome from internal carotid artery dissection, and GCA.4,5, 8-12
Anisocoria is yet another concurrent ocular symptom that sometimes manifests with diplopia that may help you specify your diagnosis. The major ocular conditions to consider when there is diplopia with anisocoria are cranial nerve III palsy and Horner's syndrome. As discussed, a CN 3 palsy may present with a dilated pupil on the affected side. A Horner's syndrome presents with a miotic pupil, and often presents with anhidrosis and ptosis on the affected side.4,5,12
If diplopia is associated with blurry vision or is followed by vision loss (partial or complete), you need to be on high alert for a neuro-ophthalmic emergency. Conditions to consider with this presentation include stroke, GCA, thyroid eye disease, and orbital lesions or inflammation.4, 8-10, 13, 14
Hopefully, this guide has served as a good review for your existing knowledge of diplopia. Now that you have double checked all the common causes of diplopia, you will be ready to tackle any double vision cases that walk into your exam room!
