eMedicine Specialties > Ophthalmology > Neurologic Disorders

Diplopia

Author: Izak F Wessels, MB, BCh, MMed, FRCSE, FRCO, BSc, FACS, 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: Sep 2, 2008

Introduction

Background

The term diplopia is derived from 2 Greek words: diplous, meaning double, and ops, meaning eye. Diplopia (double vision) is a common subjective complaint, or diplopia may be elicited during the course of an eye examination. Diplopia is often the first manifestation of many systemic disorders, especially muscular or neurologic processes. An accurate, clear description of the symptoms (eg, constant or intermittent; variable or unchanging; at near or at far; with one eye [monocular] or with both eyes [binocular]; horizontal, vertical, or oblique) is critical to appropriate diagnosis and management.

Binocular diplopia can be corrected by covering either eye; monocular diplopia persists in one eye despite covering the other eye. Physiologic diplopia is a normal phenomenon depending on the alignment of the ocular axes with the objects of regard (eg, focusing on a finger held close results in distant objects being blurry but double).

Animal models

Unless the visual fields of the eyes overlap, binocular diplopia cannot occur. Among vertebrates, the potential for diplopia (and for stereoscopic depth perception) depends on where the eyes are located in the head. Eyes located on either side of the head provide a wide visual field but with a less overlapped visual field. These animals have less field for binocular vision and less risk for diplopia when one eye becomes misaligned. However, when both eyes are located in the front of the head, a greater visual field overlap exists and, thus, a better binocular depth perception, as frequently seen in predators. Misalignment of such eyes may result in diplopia. Monocular diplopia is often due to optical aberrations resulting in multiple images.

The eyes of birds demonstrate many unique anatomical features, one of which is the presence of multiple foveae and, in some cases, a streak fovea linking 2 foveae. Thus, they may be able to have 2 separate areas of regard without disabling diplopia. How the visual perception occurs in these cases remains debatable.

Pathophysiology

Binocular diplopia (or true diplopia) is a breakdown in the fusional capacity of the binocular system. The normal neuromuscular coordination cannot maintain correspondence of the visual objects on the retinas of the 2 eyes. Rarely, fusion cannot occur because of dissimilar image size, which can occur after changes in the optical function of the eye following refractive surgery (eg, LASIK) or after a cataract is replaced by an intraocular lens.

The distortion of one image may be interpreted as diplopia by the patient; however, the same object does not appear to be in 2 places but rather appears differently with each eye.

Monocular diplopia may occur from abnormal ocular media (eg, corneal distortion or scarring, multiple openings in the iris, cataract or subluxation of the natural lens or pseudophakic lens implant, vitreous abnormalities, retinal conditions). Monocular diplopia must be distinguished from metamorphopsia, in which objects appear misshapen.

Frequency

United States

No figures are available as to prevalence of diplopia in the United States.

International

International incidence rates of diplopia are unknown.

Mortality/Morbidity

Divergent pathological processes, each with its own morbidity and mortality, can cause diplopia. However, irrespective of cause, diplopia has significant morbidity in terms of difficulty with depth perception and confusion with orientation of objects, especially when performing visually demanding tasks, such as driving a vehicle or operating tools. Therefore, in assessing visual disability after injuries, loss of binocularity accounts for a major percentage of loss of function.

Race

No information is available regarding differences in various racial groups.

Sex

No information is available suggesting differences in prevalence with respect to sex.

Age

Diplopia is encountered almost exclusively in adults or in those with mature visual systems because of the following:

• Young children may not be able to express this symptom. More importantly, the immature visual system deals with diplopia by suppressing the poorer image, possibly resulting in irreversible amblyopia. Children with obvious and marked ocular malalignment from strabismus are comfortable and content because the visual image from the deviating eye is suppressed and not noticed.
• In contrast, adults who have mature visual processing pathways cannot easily ignore the second image. Wearing a patch over one eye to prevent visual confusion usually is the only option for these patients.

Clinical

History

A clear and comprehensive history is the single most useful evaluation in treating patients with diplopia. The patient typically presents with a history of double vision, where single objects appear as double. Specific inquiry as to onset, progression, and variability with head posture or gaze direction, as well as previous similar episodes (especially if associated with other neurologic symptoms) and/or spontaneous resolution, is very helpful in the diagnosis and management of diplopia.

• Three important symptoms should be elicited, as follows:
  • Does covering either eye make the diplopia disappear? This test helps to rule out monocular diplopia, which persists in one eye even if the other eye is covered.
  • Is the deviation the same in all directions of gaze or by tilting and rotating the head into different positions? This suggests a comitant deviation, with no difference in separation of the images in all directions of gaze. When the extent of deviation changes (and indeed possibly disappears in a given direction), then the deviation is incomitant and suggests a problem with innervation, most likely a paretic muscle.  
  • Is the second object displaced horizontally (side-by-side images) or vertically (images above each other)? Oblique diplopia (images separated horizontally and vertically) should be considered as a manifestation of vertical diplopia. 
• The traditional and detailed evaluation of the chief complaint includes onset (abrupt or slow), severity, duration, location, associated symptoms, and aggravating and relieving factors. A comprehensive and complete review of all these aspects, if necessary with a questionnaire, is more important than the appropriate physical examination or special tests.
• Other significant aspects include a review of systems (eg, history of diabetes, vascular disease, or hypertension; headache and other neurologic complaints; muscle fatigue or weakness; medications and drugs being used), as well as a past medical and surgical history.
• Inquire about recent trauma to the face and the head. Blunt injury to the cheek can result in a blow-out fracture of the orbit with hematoma or entrapment of the soft tissues and extraocular muscles, restricting upward and downward eye movement. Entrapment of the inferior rectus muscle can be confirmed by a forced duction test. Blunt head injury may also be associated with nonspecific sixth cranial nerve (abducens) weakness and severe diplopia when gazing to the affected side.

Physical

Evaluate the ocular system with respect to 2 specific aspects: first, physiologically (in turn also with 2 aspects, ie, sensory function and motor function), and, second, anatomically.

• The first aspect of the physiologic evaluation includes the sensory component.
  • Confirm that the symptom is monocular or binocular. Does covering each eye in turn alleviate the problem, or does the diplopia persist despite covering the "good" opposite eye? Monocular diplopia is very uncommon. Possible causes include severe corneal deformity or marked astigmatism (keratoconus), multiple pupils or openings in the iris, refractive anomalies within the eye (early cataracts or partially displaced lenses as in Marfan syndrome), as well as retinal abnormalities (macular scarring and distortion).
  • Evaluate the magnitude of difference in spectacle correction required for each eye. Marked differences between the eyes (anisometropia) will frequently produce disabling diplopia, especially in extremes of gaze.
  • Determine the visual acuity in each eye separately, with and without spectacle correction and with a pinhole. Does a pinhole improve the visual acuity, or does it improve monocular diplopia? Major improvement in visual acuity with a pinhole suggests intraocular or refractive problems.
  • Evaluate the visual field by confrontation testing or formal visual field mapping to detect possible space occupying masses impinging on the visual pathways and/or cranial motor nerves. With severely constricted fields, the peripheral clues for fusion may be lacking, resulting in diplopia.
  • Determine how various directions of gaze modify the diplopia. Is the diplopia the same in the 9 cardinal directions of gaze? This includes straight ahead (primary gaze), to each side as well as up and down while looking toward that side, and straight up and down from the primary position. This evaluation can enhance subtle weaknesses of individual muscles that may not be apparent during testing of the range of movements.
  • Evaluate how tilting the head to the left or to the right alters the diplopia. The double vision will increase when the head is tilted to the same side if vertical diplopia is present due to weakness of the superior oblique muscle (innervated by the fourth cranial nerve [trochlear nerve]). Eliciting increases or decreases in the separation of the 2 images is an essential part of the Park three-step test.
• Evaluate the integrity of the other cranial nerves (eg, facial sensation [trigeminal nerve], facial muscle movements).
• The motor aspect of the physiologic evaluation includes the following:
  • Determine the existence of a normal range of ocular movements. First observe each eye separately (ocular ductions), and then observe both eyes together (ocular versions). Careful consideration of the extraocular muscle anatomy clarifies the effect of each muscle and why one direction of gaze isolates each muscle's effects.
  • Determine that each eye is able to fully adduct (turn inward) and abduct (turn outward) and to fully elevate and depress in abduction and adduction (as if the eye is tracing a capital letter "H").
    • This helps to determine which eye muscle is responsible for diplopia; normal contraction of the medial rectus muscle produces adduction, while abduction is caused by the lateral rectus muscle. Because the vertical eye muscles diverge from their origination at the apex of the orbit to the insertion on the globe, the superior and inferior recti muscles can be evaluated best with the eye abducted.
    • With the eye abducted, the eye will move down by the inferior rectus muscle, while the superior rectus muscle will move it upward in abduction. Likewise, the oblique muscles can be isolated with the eye adducted; with the eye turned in, the inferior oblique muscle elevates and the superior oblique muscle depresses the eye. A simple rule for superior oblique weakness is "the eye that is looks highest in adduction is pointing at the affected superior oblique muscle."
  • Determine if diplopia worsens when the muscles are fatigued (eg, after strenuous use, at the end of the day). Myasthenia gravis can affect any muscle or group of muscles, and a common presenting symptom is variable diplopia. If myasthenia gravis is suspected, its diagnosis can be confirmed by intravenously injecting a short-acting anticholinesterase (ie, 10 mg/mL edrophonium chloride [Tensilon]). See Other Tests.
  • Determine that other ocular motor functions are normal.
    • Is the lid in a normal position?
    • Is the pupil response normal and symmetric with the other pupil? Pupil asymmetry is a sinister sign when associated with diplopia because it indicates involvement of the third cranial nerve (oculomotor nerve). An important diagnostic clue is provided by detecting pupil sparing but otherwise complete third nerve palsy (eg, ptosis; inability to elevate, depress, or abduct the eye). A pupil whose function is spared, particularly if associated with complaints of headache or pain around the orbit, is virtually diagnostic of diabetic third nerve palsy. This can avoid expensive and unnecessary imaging studies. Complete and spontaneous recovery after approximately 6 weeks is virtually the rule. Similar temporary mononeuritis multiplex processes can affect the sixth cranial nerve (abducens) with temporary loss of abduction.
• The anatomical evaluation includes inspection, palpation, percussion, and auscultation.
  • Inspect the head position, eyes, eyelids, orbits, and face for symmetry or displacement (upward, downward; proptosis, enophthalmos). Ptosis of the upper eyelid indicates possible third nerve lesions, while eyelid retraction suggests thyroid ophthalmopathy. Abnormal head position (especially tilting the head to one side) suggests superior oblique muscle palsy.
  • Note inflammation or vascular congestion that may be suggestive of orbital cellulitis, orbital tumors (rhabdomyosarcoma), arteriovenous malformation (carotid cavernous fistula), and thyroid ophthalmopathy. Palpate the orbital rim for fractures and any absences (eg, encephalocele). Palpate soft tissues surrounding the eye for tumors. Gently push on the closed eyelid to determine increased resistance (fullness of the orbit), comparing one eye to the other eye. This may disclose orbital disorders (eg, fractures, tumors).
  • Perform percussion over the bony orbital rim to disclose focal tenderness from sinus inflammation.
  • Auscultate the closed eye for the bruit of a carotid cavernous fistula.

Causes

• See Pathophysiology.

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