Diplopia is double vision caused by a defective function of the extraocular muscles or a disorder of the nerves that innervate (stimulate) the muscles.
(Sixth cranial nerve: The sixth cranial nerve is the abducent nerve, a small motor nerve that has one task: to supply a muscle called the lateral rectus muscle that moves the eye outward.
Paralysis of the abducent nerve causes inward turning of the eye (internal strabismus) leading to double vision.)
Description of Diplopia
A transient episode of diplopia is usually of no clinical significance, indicating only a brief relaxation of the fusion mechanism of the central nervous system that maintains straightness.
Causes and Risk Factors of Diplopia
Double vision is usually a symptom of strabismus (deviation or misalignment of the two eyes), although not all strabismus produces double vision. In this condition, movement of the eye in a particular direction is impaired due to paralysis of one or more muscles. Tilting or turning the head can sometimes overcome the double vision.
A growth in the eyelid pressing on the front of the eyeball can also cause temporary image separation by distorting the shape of the front of the eye and by causing a slight displacement in the path of light rays entering that eye (and thus variation in the points at which they are focused on the retina). Double vision may also be caused by a tumor or blood clot behind the eye that prevents the normal motion of the eyeball.
In endocrine-related exophthalmos, protrusion of the eyeballs is the result of an underlying hormonal disorder and double vision results from swelling and scarring in the eye muscles, causing abnormal alignment and motion of the eyes.
Rarely, double vision arises because of an abnormality within the eye. For example, a dislocation of the lens in the eye may result in some light rays passing through the lens and others around it, so that separate images fall on the retina of one eye.
Treatment of Diplopia
The brain of a young child with strabismus (congenital, accommodative, or paralytic) learns to suppress the second, unwanted image seen by the misaligned, strabismic eye so as not to see double. Continued misalignment of the child's eyes may eventually lead to poor vision in the affected eye. The poor vision is called amblyopia, or lazy eye. Patching of the better-seeing eye may improve the vision in the poorly seeing, deviated eye.
The strabismus may need to be corrected early (by means of glasses and/or surgery) in children to prevent amblyopia from developing. Otherwise, it may become permanent. A young child with strabismus should be seen by a physician to find the cause and to begin treatment.
The onset of double vision in adult life needs immediate investigation to exclude the possibility of a tumor, aneurysm, and/or neurologic abnormality. The double vision could be a symptom of a very serious underlying disorder that requires prompt attention and treatment, including surgery.
Questions To Ask Your Doctor About Diplopia
How serious is this?
What caused the problem?
Should a specialist be consulted?
What type of treatment will you be recommending?
If nothing is done about this problem, what is likely to happen?
Case Presentation
A 65 year old man presented to the ED complaining of acute onset double vision. He denied headache, fever, weakness, dizziness, trauma, or change in mental status. Past medical history was positivefor diabetes and hypertension. Medications included insulin andenalapril. He denied tobacco use or alcohol use. On physical exam: BP 160/90, P 80, RR 16, T 98, pulse ox 99%. Head atraumatic, no scalp tenderness; eyes visual acuity 20/30 (corrected); pupils 4 mm and reactive; OS ptosis; OS pupil in a down and out position. Diplopia was minimal when looking to the left and pronounced when looking to the right. Fundi sharp discs. Rest of the neurologic exam was normal.
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Diplopia
Introduction
Diplopia, or the subjective report of seeing two images instead of one, is an uncommon complaint in the ED yet is still encountered with enough frequency that emergency physicians should be comfortable in approaching these patients. Diplopia is one of the chief complaints that uncommonly has serious causes; there are a few important “don’t miss” diagnoses.
For the most part, this discussion focuses on diplopia as a chief or presenting complaint. Diplopia as an additional symptom to another complaint such as diffuse weakness or hemiparesis is not covered here. Diplopia with multiple cranial nerve palsies or paralysis, for example, is a subject not covered.
This simple review is meant to compliment the FERNE presentation on the topic; for detailed and esoteric discussion the physician is referred to any of a comprehensive references-of which there are many- listed at end of this discussion. It is important to balance the reviews by realizing some are written with the bias of neurologists, some ophthalmologists, and others even more sub-specialized physicians.
Epidemiology
A recent literature search for evidence-based data on diplopia in the emergency department yielded one article (Morris), and that from an ophthalmologic hospital in London. The incidence of diplopia as a chief complaint in ED’s must be low but is unknown. In this eye-only facility, diplopia accounted for 1.4% of the chief complaints.
From the report of Morris, we can extract some of the relative frequencies of the different causes of diplopia as a presenting complaint. Monocular diplopia, that is the double images from only one eye, was surprisingly high accounting for 25% of the cases. This seems high, particularly with one old clinical axiom that states that monocular diplopia is often psychogenic, and must reflect the large number of patients with refractive errors seen at that facility. Binocular diplopia accounted for the majority of cases with isolated cranial nerve palsies accounting for the largest portion of binocular diplopia.
Pathophysiology
Complex integrated interactions exist for many different areas of the brain -cortical and subcortical, neuromuscular transmission, and refractive and receptive properties of the eye to work in concert to result in normal stereoscopic vision. Fixation of an image on the central fovea of both eyes and maintaining this fixation through movement of the object, the eyes, the head, the body, perhaps while in a vehicle is complex and the possibilities of dysfunction are myriad. Simply tracking an object involves the perception of motion, complex brainstem interactions involving cortical and subcortical areas, interneurons and pathways, multiple cranial nerves with intact muscular “yoking”, and correct functioning of the mechanical operations of the globe.
Monocular diplopia usually results from some dysfunction in refraction, most often the lens but potentially involving the cornea or retinal (rare reports of CNS). In the series by Morris, problems with the lens accounted for about 40% of these problems and corneal problems another 25%. No causes was established in slightly more than 10% of cases.
Extra-ocular – problem with corrective lens or contacts
Ocular - corneal abrasion, infection, trauma, keratoconus
Iris – pharmacologic mydriasis
Lens - opacities, cataracts, following lens implant, problems with implant
Retinal – detachment, central retinal venous occlusion, neovascularization
No causes / possible psychogenic
Binocular diplopia is the more common presentation. Causes may be from inappropriate motion of the globe (mechanical impediment or neuromuscular problem); cranial nerve dysfunction either from impairment of the cranial nerve itself or cortical dysfunction. Even subtle dysfunction may result in the subjective complaint of diplopia. The intracranial anatomy is of course complex and come references devote extensive attention to localizing the site of cranial nerve dysfunction such as intra-cavernous sinus, extra-cranial, etc. Again, the series by Morris gives us an idea of the conditions that may be encountered with some frequency. Isolated dysfunction of a cranial nerve accounted for about 40% of the cases of binocular diplopia, Muscular problems accounted for about 15% including thyroid myopathy and myasthenia. Variants of Guillain-Barre syndrome, though not encountered in this series, may also present with diplopia. No causes was established in about 10% of cases.
Cranial nerve palsy (III, IV, or VI) – below the nucleus (“infranuclear”)
Orbital - cellulitis, abscess, tumor
Trauma- blunt, blowout fractures
Supranuclear neurologic lesions
Lens - opacities, cataracts, following lens implant, problems with implant
Retinal – detachment, central retinal venous occlusion, neovascularization
No causes / possible psychogenic
Problems with cranial nerves resulting in diplopia may stem from dysfunction of cranial nerves III, IV, or VI and may be obvious or subtle.
In the illustration above (modified from reference 2) – the patient is observed while attempting to fixate on an object straight ahead. The right eye is fixed on the target while the patient’s left is abnormally deviated downward and outward. The diplopia is greatest when looking to the patient’s right and lessens when looking to the left. Note that the pupil is slightly larger in the left eye and would be poorly reactive if tested. This is the classic cranial nerve III palsy with pupillary involvement, likely from a compressive lesion affecting cranial nerve III. Note also the presence of ptosis (the examiner is lifting the ptotic lid) which often accompanies a cranial nerve III palsy. These signs show the need for prompt imaging and consultation since an intracranial aneurysm may cause this clinical picture.
A classic axiom is that the cranial nerve III palsy that may result from diabetes spares the action of the pupil (“pupillary sparing”) and is painless. Many recommend following these patients expectantly and not pursuing emergency imaging studies.
Cranial nerve VI dysfunction results in failure of abduction (away from midline) of the globe since the innervation to the lateral rectus is impaired. This may be brought out on examination or an abnormally medially deviated eye may be present on simple inspection. Cranial nerve VI has the longest intracranial course and may be impaired from the effects of increased intracranial pressure.
Cranial nerve IV dysfunction may be quite difficult to detect clinically. Cranial nerve IV innervates the superior oblique muscle which intorts the eye as well as depressing the globe. In patients with fourth cranial nerve palsies, the loss of normal superior oblique function may make the eye appear to be relatively elevated, especially if examined with the affected eye adduction (tracing medially then up and down).
From Morris’ series, infranuclear cranial nerve palsies accounted for 40% of the cases of binocular diplopia.
Cranial nerve III palsy- diabetes, other vascular cause / aneurysm, pituitary tumor.
Cranial nerve IV- congenital, diabetes / vascular, trauma
Cranial nerve VI- diabetes, multiple sclerosis, CNS tumor, pseudotumor
Binocular diplopia from CNS lesions above the level of the cranial nerve do occur and were detected in Morris’ series representing a total of 7% of the causes. Brainstem ischemia, migraine, Wernicke’s encephalopathy, and multiple sclerosis (with bilateral internuclear ophthalmoplegia (BINO- a topic for another day) were all encountered.
Emergency Department Approach
The approach in the emergency department is to first screen for other signs and symptoms that may accompany the complaint such as weakness, other cranial nerve or CNS dysfunction, or problems with the eye itself. History of severe headache, recurrent weakness, or paralysis points to a more general problem ( and is outside of this discussion).
Next, examination should determine if the diplopia persists with one eye covered and if it is localized to one globe, that is, define whether the diplopia is binocular or monocular. Examination that reveals proptosis or exophthalmos suggests abnormal mass within the orbit.
Cranial nerve exam should note ptosis; ptosis with impairment of the extraocular movements strongly points to cranial nerve III dysfunction (while ptosis and miosis are components of Horner’s syndrome).
Historical details such as associated medical conditions, the nature of the onset of the diplopia, any prior occurrences, and the presence of absence of pain should be noted.
If the problem is binocular diplopia, and the absence of other signs and symptoms points to a possible cranial nerve problem, a few rules (“laws of diplopia” DeMyer) may help isolate the problem. DeMyer suggests identifying the position of maximum diplopia and then identifying the eye that the false image is originating from by covering and uncovering the eye. When the patient looks in the direction of the paretic eye, the distances between images increases. The false/erroneous image is projected peripheral to the true image and is often less sharp (since it is not projected on the fovea); the red-glass test helps the patient in separating images. By identifying the paretic muscle, the associated cranial nerve may be identified.
CT Scanning / other imaging
Many of the caveats regarding neuroimaging seem to date from pre-CT and MR times when the risk of neuroimaging-angiography- was not inconsequential. The axioms seem to be standing the test of time since they are repeated in the literature.
Generally speaking, liberal neuroimaging with new cranial nerve function is suggested and consultation may be useful in selecting the preferred test—CT vs MRI/MRA. The continued lack of expedient MRI to emergency departments remains a factor.
The old clinical axiom—that an isolated third nerve palsy that is pupillary sparing in a diabetic –may be managed without neuroimaging seems to be holding; at least there are no data that contradict it. However, if the pupil is not normal or is abnormal, the patient is not diabetic, another other signs or symptoms point to a possible CNS problem, imaging should be pursued. Most would agree that neuroimaging is warranted in all other cases of cranial nerve dysfunction, particularly with cranial nerve VI, since dysfunction may reflect focal abnormalities or diffuse elevated intracranial pressure.
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Diplopia
Annotated Bibliography
1.) Solomon P, Aring CD: The causes of coma in patients entering a general hospital. Am J Med Sci 1934;188:805.
Quotation reference from presentation.
2.) Laskowitz D, Liu GT, Galetta SL: Acute visual loss and other disorders of the eyes. Neurologic Cl N Am 1998;16:323.
Photographic source for presentation. Neuro-opthalmologists writing crisp yet erudite summary of visual problems including diplopia.
3.) Morris RJ: Double vision as a presenting symptom in an ophthalmic casualty department. Eye 1991;5:124.
The only prospective series of patients presenting to an emergency facility (an ophthalmologic facility). Reference may give some perspective on relative frequencies of different conditions. The case series served as a springboard for discussion in this presentation.
4.) Eggenberger ER, Hodge T: Neuro-ophthalmology. In: Shah SM, Kelly KM: Emergency Neurology: Principles and Practice.
Contains an expanded differential diagnosis of diplopia found in medical and neurologic conditions.
5.) Richardson LD, Joyce DM: Diplopia in the emergency department. Em Med Cl N AM 1997;15:649.
Another review of diplopia in the emergency medicine literature by emergency physicians. Anatomy and physiology briefly reviewed.
6.) Records RE: Monocular diplopia. Surv Ophth 1980;24:303.
Summary of common causes of monocular diplopia as well as the rare neurologic causes.
7.) DeMyer W: Technique of the Neurologic Examination. McGraw-Hill, 1994.
Summarizes exam technique and “laws of diplopia.”
8.) Patten J: Neurological Differential Diagnosis. Springer-Verlag, 1996.
Richly illustrated chapter on cranial nerve abnormal ties; lists a specific question-guided historical approach to the patient.
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Questions
1.) From available data, what is the approximate ration of patients presenting with diplopia to an emergency facility with monocular vs. binocular diplopia?
a. 1:100
b. 1:10
c. 1:4
d. 1:1
2.) Supranuclear lesions that may present with diplopia include all of the following except:
a. Multiple sclerosis
b. Myasthenia gravis
c. Brainstem ischemia
d. Wernicke’s encephalopathy
3.) Which of the following pairs of cranial nerves and extraocular motion is incorrect?
a. Cranial nerve III : depression
b. Cranial Nerve IV: adduction
c. Cranial nerve IV: Intorsion
d. Cranial nerve VI: abduction
4.) Patients presenting with all of the following should have immediate neuroimaging and consultation except
a. Sixth cranial nerve palsy
b. Third cranial nerve palsy with large poorly reactive pupil
c. Third cranial nerve palsy with reactive pupils in patient with diabetes
d. All should get immediate CT
Answers
1.) Answer: c
2.) Answer: b
3.) Answer: b
4.) Answer: c
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