Summary
Diplopia or double vision is the separation of images vertically, horizontally or obliquely and can be of monocular or binocular origin. Binocular diplopia is most commonly caused by ocular misalignment or strabismus which can be detected by simple clinical tests.
All patients with acute-onset diplopia should be investigated urgently and those with headache or pupillary involvement should be referred for urgent imaging on the same day. Diplopia secondary to microvascular causes, on the other hand, often resolves spontaneously within six months.
Key points
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Diplopia or double vision is a condition in which an object is seen as a double image. The two images may have the same intensity, or one may appear as a ghost or faint image. They can be seen side by side, on top of each other or tilted, and this can vary in different directions of gaze.
Diplopia is usually binocular when it occurs only when both eyes are open and disappears when one eye is closed, or monocular when it persists even after one eye is closed. It can be a benign condition, but can sometimes herald a significant underlying condition that requires investigation and treatment.
The physiology of binocular vision
Binocular vision is a complex phenomenon that is based on several components working together. The eyes are moved by six extraocular muscles : lateral rectus (LR), medial rectus (MR), inferior rectus (IR), superior rectus (SR), inferior oblique (IO) and superior oblique (SO).
These, in turn, are controlled by three cranial nerves , called the third, fourth and sixth cranial nerves, with the sixth nerve innervating the LR, the fourth the SO and the third the MR, IR, SR and IO. These cranial nerves arise in the midbrain (third and fourth nerves) and pons (sixth nerve), with the nuclei joined by the medial longitudinal fasciculus.
The output of these, in turn, is coordinated by the supranuclear gaze centers. The center of horizontal gaze is in the pons in the parapontine reticular formation (PPRF) and the center of vertical gaze is in the reticular formation of the midbrain and pretectal area. Additionally, images are affected by head position, governed by the vestibular reflex (VOR).
By adjusting the position of the eyes to counteract head movement, the VOR stabilizes the image on the retina and prevents blurring. These images are transmitted to the brain through the optic nerve and visual pathways, where visual processing occurs to form a single composite image.
Causes of diplopia
binocular diplopia
Under normal viewing conditions, each eye sends a slightly different image to the brain and cortical fusion mechanisms join the two images, using the slight disparity between them to create the illusion of three-dimensional vision, or stereopsis.
If the images sent to the brain are very different due to misalignment of the eyes, diplopia occurs. This misalignment of the eyes is called strabismus (strabismus) and can be vertical, horizontal, or torsional. Strabismus can be secondary to neurological or mechanical factors and is almost always acquired if it is associated with diplopia.
Rarely, after central neurological trauma or injury, such as a stroke, the brain loses its ability to fuse these images despite good alignment ( horror fusionis ).
monocular diplopia
This variety of double vision persists even if one eye is closed and is associated with ocular changes such as dry eyes, corneal scarring, cataracts, retinal membranes, or non-organic causes.
The clinical history
It is essential to cultivate a logical and structured approach to the history and examination of patients with diplopia. While each case is different, using a logical approach will ensure that important clinical information is not missed and that an accurate diagnosis can be reached. Diplopia, especially of acute onset , is a red flag and the possibility of an underlying neurological cause should be seriously considered.
Guiding questions
Is the onset of double vision recent (which may indicate a neurological event) or long-standing (decompensated strabismus, which is less urgent)? Patients may remember an antecedent event, such as a head injury, cerebrovascular event, or sinus surgery.
Does double vision disappear after closing one eye (binocular diplopia, which is more likely to require intervention) or does it persist (monocular diplopia, which is likely due to local or non-organic ophthalmic causes)?
Are the images separated horizontally (suggesting divergent or decompensated convergent strabismus, sixth nerve palsy, or internuclear ophthalmoplegia secondary to multiple sclerosis) or vertically (suggesting third and fourth nerve palsies or restrictive disorders such as burst fracture or disease thyroid of the eye)?
Are there any associated symptoms such as ptosis (third nerve palsy, myasthenia), blurred vision (third nerve palsy due to dilated pupil), headache (elevated intracranial pressure), weakness, fatigue or difficulty swallowing (myasthenia, demyelinating disorders) , oscillopsia (due to nystagmus in internuclear ophthalmoplegia), eyelid retraction or proptosis (thyroid eye disease), temporal headache and pain when swallowing (temporal arteritis or giant cell arteritis [GCA]), or abnormal head posture?
Previous ophthalmic history
Ask specifically about glasses/contact lens use and whether their use improves strabismus (suggesting long-standing decompensated strabismus). Are they using any prisms in their glasses? Do they have a history of occlusion of either eye in childhood signifying underlying amblyopia (suggesting long-standing strabismus)?
Have they suffered any previous eye trauma or undergone any refractive or strabismus surgery?
Medical history
It is important to identify disorders such as hypertension and diabetes, previous strokes, and vascular risk factors. These are especially important in determining causality in cranial nerve palsies, as most vascular nerve palsies recover within the first 6 months and therefore only require observation or non-invasive treatment. Other systemic conditions associated with diplopia include hyperthyroidism and myasthenia gravis.
Of note, headache and pupil involvement can be seen in microvascular nerve palsies as well as surgical cranial nerve palsies and therefore this does not help to distinguish between the two.
Drugs such as lamotrigine, topiramate, gabapentin, fluoroquinolones, and citalopram have been associated with diplopia, but this occurs infrequently.
Family history
A family history of strabismus, amblyopia, and high refractive errors may signify a genetic component.
Physical exam
Assess visual acuity with distance glasses or contact lenses in each eye. Close each eye to investigate whether the diplopia is monocular or binocular.
Perform a corneal reflex test by shining a flashlight about 33 cm away so that you can see your reflection in both pupillary areas. This will immediately detect any obvious strabismus and estimate the size of the deviation (30 diopters if the reflection is at the edge of the pupil, 45 diopters if it is between the pupil and the limbus, and 60 diopters if it is at the edge of the limbus).
In a sixth nerve palsy , the eye will be deviated inward, in a third nerve palsy it will be deviated downward and outward, and in a fourth nerve palsy , the affected eye will be higher, especially in medial gaze.
Assess ocular motility by asking the patient to follow the flashlight light or fixation target (finger, pen) while moving it in all nine gaze directions, in a cross-shaped pattern, asking you to say whether the object bends at any stage.
If the patient describes diplopia, ask if it is vertical or horizontal ("Are the images side by side or on top of each other?" ), which will help elucidate the type of deviation (sixth nerve palsy leads to horizontal separation; the fourth and third nerve palsy can cause both horizontal and vertical separation; thyroid eye disease and burst fracture are predominantly associated vertical separation). Oblique diplopia means both a vertical and horizontal component. The separation will increase in the field of maximum limitation.
The eye examination can provide useful clues about the associated pathology:
- Ptosis suggests myasthenia or third nerve palsy.
- Eyelid retraction suggests thyroid eye disease.
- Nystagmus suggests demyelination.
- Proptosis suggests thyroid eye disease.
- Papilledema may indicate increased intracranial pressure.
A fixed dilated pupil associated with headache and diplopia is a neurosurgical emergency and requires urgent imaging.
Systemic examination
All patients with diplopia should undergo a complete examination of the cranial nerves and peripheral nervous system, since palsies of several cranial nerves can mean intracranial or meningeal tumors, meningitis, polyneuropathy, multiple sclerosis, or lesion of the cavernous sinus. It is also helpful to look for signs of thyroid dysfunction if indicated.
Research
It is useful to measure blood pressure and blood glucose and perform urinalysis for suspected microvascular cases, thyroid function testing or orbicularis single fiber EMG, and acetylcholine receptor antibodies for myasthenia.
Imaging (an MRI or CT angiography) may be indicated if the onset is acute and/or associated with neurological signs or papilledema.
Clinical management
All patients with new-onset diplopia should be advised to stop driving.
Most microvascular causes of diplopia can be seen if the rest of the examination is normal, as they usually resolve spontaneously within 6 months. They may benefit from referral to the ophthalmology department as diplopia can be relieved with prisms, patches or toxin in the meantime.
Urgent same-day imaging should be sought for patients with a fixed dilated pupil, headache, and diplopia. Acute medical referral or rheumatology should be performed if associated giant cell arteritis is suspected . Other symptoms of giant cell arteritis include weight loss, night sweats, temporary headache, jaw claudication, and vision loss.
