eMedicine Specialties > Ophthalmology > Neurologic Disorders

Diplopia: Differential Diagnoses & Workup

Author: Izak F Wessels, MBBCh, MMed, FRCSE, FRCO, Associate Professor, Department of Ophthalmology, Chattanooga Unit, University of Tennessee College of Medicine; Private Practice in Comprehensive and Surgical Ophthalmology, Allied Eye Associates
Contributor Information and Disclosures

Updated: Nov 19, 2009

Differential Diagnoses

Other Problems to Be Considered

Malingering/hysteria
Middle ear disease with vertigo
Anisometropia
Diabetic mononeuritis multiplex
Encephalocele
Polycoria

As with any subjective complaint, individuals who are hysterical or malingering may complain of diplopia (double vision). Photopsias and scotomas that occur during the aura of classic migraine may be interpreted erroneously as diplopia. Since the visual axes can only really coincide in one location in three-dimensional space, objects in front of or behind appear double. This can be demonstrated easily by focusing on a finger held out at an arm's length. Objects behind the finger appear blurry and double. Shifting the focus to an object in the same direction but behind the finger results in the object becoming single, while the finger appears blurry and double. Suddenly becoming aware of this diplopia represents a disorder of higher cerebral function.

Workup

Laboratory Studies

• Perform laboratory studies as indicated by aspects disclosed after a comprehensive history and physical examination with emphasis on ocular findings and neurologic screening.

Imaging Studies

• Evaluate old photographs to determine if a head posture (if present) is long-standing. Commonly, a congenitally weak superior oblique muscle can be compensated for by head tilt, but osteoarthritis of the neck or other mechanism can result in decompensation and sudden symptoms of a chronic subclinical condition.
• Order CT scan or MRI (with contrast) of the skull and orbits to rule out intracranial masses or other pathologic processes, such as the following:
  • A blow-out fracture requires imaging of the orbital floor.
  • Enlarged muscles from thyroid ophthalmopathy help explain a vertical diplopia.
  • Tumor of orbit
  • Tumor along cranial nerve pathway
  • Increased intracranial pressure can account for bilateral abducens palsy.
  • Aneurysm of intracranial carotid artery
  • Carotid cavernous fistula: Angiography may be required to confirm the presence of a low-flow fistula.
  • Disease of sinuses (eg, infection, tumor) or bony disorders (eg, dysostoses, encephalocele) can account for displacement of the eye.

Other Tests

• Tensilon test is performed to exclude myasthenia gravis.
  • Intravenous injection of a short-acting anticholinesterase (ie, 10 mg/mL edrophonium chloride [Tensilon]) should be part of the initial workup of a patient with diplopia. Draw up 1 mL, and establish venous access. Then, inject a test dose of 1 mg intravenously to exclude possible hypersensitivity; if no adverse effect is evident, inject the remaining 9 mg.
  • The expected (normal) cholinergic response includes salivation; lacrimation; flushing; and a brief, but often quite dramatic, reversal of muscle weakness with temporary correction of diplopia and/or ptosis. Occasionally, an excessive cholinergic response may result in increased vagal tone with serious bradyarrhythmias; atropine (0.5 mg) should be available as an antidote.
  • Other myopathies (eg, progressive external ophthalmoplegia, myotonia) do not respond to anticholinesterases.
• Forced duction test: If a lack of movement of one eye occurs in a given direction, excluding a tethered (or fibrotic) muscle may be helpful. Evaluate whether the globe can be passively moved toward the affected area. Traditionally, a forceps is used (after topical anesthesia) to grasp the limbus, and then the eye can be gently tugged in the desired direction. It may be possible to achieve the same result less traumatically by using a cotton wool bud (soaked in topical anesthetic) to "push" on the limbus in the desired direction.
• Lee screen: This highly specialized test separates the field of vision of the 2 eyes. With one eye, the subject fixates on the corners of a rectangle. The other eye is used to visualize the placement of a marker on the same location. Any overaction or underaction will become evident; when one eye has a weak muscle, it will not move as much as the other eye. However, if that eye is used to fixate, the excessive stimulation required will result in an overshoot of the normal yoke muscle in the opposite eye.
• Park three-step test
  • The Park three-step test can help elucidate which of the 4 extraocular muscles responsible for vertical eye movements are responsible for a vertical diplopia. Although first appearing impossibly complex, this test follows a logical progression to progressively eliminate groups of muscles from the 4 pairs.
  • First, determine which eye appears higher with the head in a normal position. Then, determine which eye is higher with gaze to the left or to the right (ie, with the head turned to the right and then turned to the left). Lastly, determine which eye is higher with the head tilted left and tilted right. (The patient can also help by commenting about when the diplopia is worse.) Then, answer the questions in the following steps:
    • Step 1: Is the left eye or the right eye higher in primary gaze? This reduces the possibilities of muscles from 4 pairs to 2 pairs. For example, if the right eye is higher, the weakness resides either in the muscles depressing the right eye (right superior oblique muscle and right inferior rectus muscle) or in the elevators of the left eye (left superior rectus muscle and left inferior oblique muscle).
    • Step 2: Is the deviation greater with left head turn or with right head turn? This step reduces the alternatives to only one pair of muscles. If the right eye deviates most when the head is turned to the right (both eyes are turning to the left), then only the right superior oblique muscle or the left superior rectus muscle remains.
    • Step 3: Is the deviation greatest with tilting the head to the left or to the right? Called the Bielschowsky head tilt, it relies on the torsional balancing reflexes provoked by head tilt. The higher eye extorts (because of the inferior oblique muscle), while the lower eye intorts (because of the superior oblique muscle).
  • By combining steps 1-3, only one muscle remains as the culprit. This test requires a logical analysis and the exclusion of alternative possibilities. However, the astute clinician can greatly simplify this process by recognizing that the superior oblique muscle is by far most likely to be responsible for a vertical diplopia. A head tilt to the same side as the involved muscle exacerbates the problem. A very simple rule of thumb is that "the eye that is highest in adduction looks at the affected muscle."
• The severity of the diplopia can be quantified by plotting the field of single binocular vision on a Goldmann perimeter (when available) or by using either a device to standardize the head position or a questionnaire.^3,4  
  • The Cervical Range of Motion (CROM) device uses a head-mounted device with direction indicators to reproduce specific gaze positions (10 degrees and 30 degrees up; down, left, right, straight ahead, and reading position).
  • The questionnaire assigns a score of 6 if the diplopia is always present straight ahead, a score of 4 if the diplopia is present in the down, right, left, and reading position, and a score of 2 if the diplopia is present in upgaze. The scores are halved if the diplopia is sometimes present in these gaze directions.

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