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Diplopia means the simultaneous perception of two images of a single object or seeing double is a common symptom identified in ophthalmological and neurological patients. It has many underlying causes. Efficient management implies an accurate diagnosis that can be made with a detailed history and a careful clinical examination. The assessment of the patient’s perception of diplopia must exclude other symptoms that can be misunderstood by the patient, such as image distortion, visual field defects, after images, hemianopia.
Diplopia, commonly known as double vision, is the simultaneous perception of two images of a single object that may be displaced horizontally, vertically, diagonally (i.e., both vertically and horizontally), or rotationally in relation to each other.[rx] It is usually the result of impaired function of the extraocular muscles(EOM), where both eyes are still functional but they cannot turn to target the desired object.[rx] Problems with EOMs may be due to mechanical problems, disorders of the neuromuscular junction, disorders of the cranial nerves (III, IV, and VI) that stimulate the muscles, and occasionally disorders involving the supranuclear oculomotor pathways or ingestion of toxins.[rx]
Types of Diplopia
- Monocular diplopia - is a double vision in only one eye. The double vision continues even when the other eye is covered. The doubling does not go away when you look in different directions. Diplopia can also occur when viewing with only one eye; this is called monocular diplopia, or, where the patient perceives more than two images, monocular polyopia. While there rarely may be serious causes behind monocular diplopia symptoms, this is much less often the case than with binocular diplopia.[rx]
- Binocular diplopia - is double vision related to a misalignment of the eyes. The double vision stops if either eye is covered. Any problem that affects one or more of the muscles around the eyeball that control the direction of the gaze can cause binocular diplopia. These are called extraocular muscles. Binocular diplopia is double vision arising as a result of strabismus (in layman's terms cross-eyed), the misalignment of the two eyes relative to each other either esotropia (inward) or exotropia (outward). In such a case while the fovea of one eye is directed at the object of regard, the fovea of the other is directed elsewhere, and the image of the object of regard falls on an extra-foveal area of the retina.
- Temporary - Temporary binocular diplopia can be caused by alcohol intoxication or head injuries, such as concussion (if the temporary double vision does not resolve quickly, one should see an optometrist or ophthalmologist immediately). It can also be a side effect of benzodiazepines or opioids, particularly if used in larger doses for recreation, the anti-epileptic drugs Phenytoin and Zonisamide, and the anticonvulsant drug Lamotrigine.
- Voluntary - Some people are able to consciously uncouple their eyes, either by over-focusing closely (i.e. going cross-eyed) or unfocusing. Also, while looking at one object behind another object, the foremost object's image is doubled (for example, placing one's finger in front of one's face while reading text on a computer monitor). In this sense double vision is neither dangerous nor harmful, and may even be enjoyable. It makes viewing stereograms possible.[rx]
Supranuclear pathways comprise those that are used for volitional eye movements and the vestibular input that tweaks the eye position relative to the head position. Horizontal eye movements are regulated by a specific area called the paramedian pontine reticular formation (PPRF). When a lesion involves this region, the horizontal eye movements are restricted symmetrically. As a result of the symmetry, patients do not usually complain of diplopia. However, there are some supranuclear lesions that asymmetrically affect the area of interest. Skew deviation is one of the best examples. This is a vertical misalignment that can result from posterior fossa (either in the brainstem or cerebellum) or inner ear lesions. It can be either competent or incompetent and may even present similarly to fourth nerve palsy. However, the Parks-Bielschowsky three-step test (described later) is useful in differentiating the two conditions.
The typical internuclear cause of diplopia is the internuclear ophthalmoplegia (INO). Demyelination is the most frequent etiology in younger patients, whereas microvascular ischemic stroke is more common in the older population. INO results from the disruption of the medial longitudinal fasciculus (MLF) which connects the ipsilateral sixth nerve nucleus in the pons to the contralateral third nerve nucleus in the midbrain. It classically presents with reduced adducting saccadic velocity in the eye ipsilateral to the lesion as well as abducting nystagmus in the contralateral eye.
Infranuclear causes comprise the isolated ocular motor nerve palsies. The lesions can be present from anywhere the nerves exit the brainstem.
Causes of Diplopia
Diplopia has a diverse range of ophthalmologic, infectious, autoimmune, neurological, and neoplastic causes.
- Antipsychotics (Haloperidol, Fluphenazine, Chlorpromazine etc.)
- Atypical Parkinsonisms, especially multiple system atrophy (MSA) and progressive supranuclear palsy (PSP)
- Brain tumor
- Damaged third, fourth, or sixth cranial nerves, which control eye movements.
- Fluoroquinolone antibiotics[rx]
- Graves disease
- Guillain–Barré syndrome
- Lyme Disease
- Migraine headaches
- Multiple sclerosis
- Myasthenia gravis[rx]
- Orbital myositis
- Wernicke's syndrome
- Increased Intracranial Pressure (compressing 6th cranial nerve result in diplopia)
Symptoms of Diplopia
Double vision can happen with no other symptoms. Depending on the cause, you may also notice:
- Misalignment of one or both eyes (a "wandering eye" or "cross-eyed" appearance)
- Pain when you move your eye
- Pain around your eyes, like the temples or eyebrows
- Weakness in your eyes or anywhere else
- Droopy eyelids
Diagnosis of Diplopia
The examination begins with a review of vital signs for fever and general appearance for signs of toxicity (eg, prostration, confusion).
- Eye examination - It begins with noting the initial position of the eyes, followed by measuring visual acuity (with correction) in each eye and both together, which also helps determine whether diplopia is monocular or binocular. The eye examination should note the presence of bulging of one or both eyes, eyelid droop, pupillary abnormalities, and disconjugate eye movement and nystagmus during ocular motility testing. Ophthalmoscopy should be done, particularly noting any abnormalities of the lens (eg, cataract, displacement) and retina (eg, detachment).
- Ocular motility - is tested by having the patient hold the head steady and track the examiner’s finger, which is moved to extreme gaze to the right, left, upward, downward, diagonally to either side and finally inward toward the patient’s nose (convergence). However, mild paresis of ocular motility sufficient to cause diplopia may escape detection by such examination.
- Diplopia is diagnosed - mainly by information from the patient. Doctors may use blood tests, physical exams, computed tomography (CT) or magnetic resonance imaging (MRI) to find the underlying cause.[rx]
- For binocular diplopia - patients with a unilateral, single cranial nerve palsy, a normal pupillary light response, and no other symptoms or signs can usually be observed without testing for a few weeks. Many cases resolve spontaneously. The ophthalmologic evaluation may be done to monitor the patient and help further delineate the deficit.
- MRI - to detect orbital, cranial, or CNS abnormalities.
- CT - may be substituted if there is concern about a metallic intraocular foreign body or if MRI is otherwise contraindicated or unavailable. Imaging should be done immediately if findings suggest infection, aneurysm, or acute (< 3 h) stroke.
- Patients with manifestations of Graves disease - should have thyroid tests (serum thyroxine [T4] and thyroid-stimulating hormone [TSH] levels). Testing for myasthenia gravis and multiple sclerosis should be strongly considered for patients with intermittent diplopia.
Treatment of Diplopia
Treatment therapies in children include alternate patching, prism therapy, strabismus surgery, and botulism toxin. Alternate patching consists of patching each alternating eye for a few hours each day. This is used to prevent amblyopia in the affected eye. Prism therapy requires placement of a temporary press-on prism on the lens of the affected eye. If a child fails prism therapy, he or she would be eligible for strabismus surgery. Botulism can be injected into the medial rectus of the affected eye to prevent contracture and nasal deviation.[rx][rx][rx]
- For binocular diplopia - will depend upon the cause of the condition producing the symptoms. Efforts must first be made to identify and treat the underlying cause of the problem. Treatment options include eye exercises,[rx] wearing an eye patch on alternative eyes,[rx] prism correction,[rx] and in more extreme situations, surgery[rx] or botulinum toxin.[rx]
- Steroids - will be given to those suffering from temporal arteritis. In cases related to intracranial pressure, such as pseudotumor cerebri and cancer, the pressure would need to be reduced through surgery or lumbar puncture. Further treatment of persistent sixth nerve palsy would be similar to that in children, save for alternative patching, which has not proven to be effective in adults.
- Anticholinesterase medications - in myasthenia gravis and orbital decompression, strabismus surgery, and lid surgery (in this specific order) for thyroid eye disease. [rx][rx][rx]
- Immunosuppressive agents -
- Corrective lenses - Eyeglasses or special lenses may correct the vision problem. For example, prisms may be etched into the lenses of your eyeglasses to adjust your vision.
- Eye patch or cover - Covering one eye may stop the double vision. While this may not be a long-term solution, an eye cover can help manage double vision until there is a more permanent solution.
Exercises cannot treat many of the conditions that cause double vision. However, some exercises can help with convergence insufficiency.
- Focus on a detailed target, perhaps a thin stick or small text in a magazine.
- Hold this at eye-level, an arm's length away from you.
- Aim for the image to remain as a single image for as long as possible.
- Move the target towards the nose in a slow, steady fashion.
- When the single image becomes two images, your eyes have stopped collaborating. Focus intensely on bringing these images back together. Once they join, bring the target closer to the nose.
- Once you become unable to rejoin the images, move your hand back to its original position and start the exercise again.
- The normal convergence range is 10 centimeters (cm) away from the nose. Aim to keep the image as a single image up to the 10cm mark.
- An orthoptist may provide a tool known as a Dot Card to assist these steps.
- Choose a similar target to that in the smooth convergence exercise.
- Start the target at a 20 cm distance from the nose.
- Fix your gaze on the target for between 5 and 6 seconds.
- Switch to looking at a fixed object around 3 meters (m) away for around 2 to 3 seconds.
- Switch your vision back at the nearer target.
- Repeat this, gradually moving the target closer, until you can focus on the object when it is 10 cm away without double vision. The effectiveness of these exercises is largely restricted to treating convergence insufficiency.
- Depending on the cause, you might require surgery to correct any physical issues. Also, people with issues like cataracts or problems within the eye likely will need surgery at some point. The surgery to correct that problem should also fix any double vision.