Diplopia is diagnosed mainly by information from the patient. Doctors may use
blood tests, physical examinations,
computed tomography (CT), or
magnetic resonance imaging (MRI) to find the underlying cause.
Classification One of the first steps in diagnosing diplopia is often to see whether one of two major classifications may be eliminated. That involves blocking one eye to see which symptoms are evident in each eye alone. Persisting blurry or double vision with one eye closed is classified as monocular diplopia.
Binocular Binocular diplopia is the other one in which the blurring of vision occurs only when the patient looks through both eyes simultaneously. It is common and occurs in approximately 10.0% to 40.0% of zygomatic complex injuries. Furthermore, diplopia may be transient or persistent. Inadequate diagnosis and treatment at improper times and tethering or fibrosis of muscles may lead to persistent diplopia. 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 extrafoveal area of the
retina. Acute diplopia is a diagnostic challenge. The most common cause of acute diplopia are ocular motor nerve palsies (OMP). The brain calculates the visual direction of an object based upon the position of its image relative to the fovea. Images falling on the fovea are seen as being directly ahead, while those falling on retina outside the fovea may be seen as above, below, right, or left of straight ahead depending upon the area of retina stimulated. Thus, when the eyes are misaligned, the brain perceives two images of one target object, as the target object simultaneously stimulates different, noncorresponding, retinal areas in either eye, thus producing double vision. This correlation of particular areas of the retina in one eye with the same areas in the other is known as
retinal correspondence. This relationship also gives rise to an associated phenomenon of binocular diplopia, although one that is rarely noted by those experiencing diplopia. Because the fovea of one eye corresponds to the fovea of the other, images falling on the two foveae are projected to the same point in space. Thus, when the eyes are misaligned, two different objects will be perceived as superimposed in the same space. This phenomenon is known as 'visual confusion'. The brain naturally guards against double vision. In an attempt to avoid double vision, the brain can sometimes ignore the image from one eye, a process known as
suppression. The ability to suppress is to be found particularly in childhood when the brain is still developing. Thus, those with childhood strabismus almost never complain of diplopia, while adults who develop strabismus almost always do. This ability to suppress might seem an entirely positive adaptation to strabismus, but in the developing child it can prevent the proper development of vision in the affected eye, resulting in
amblyopia. Some adults can also suppress their diplopia, but their suppression is rarely as deep or as effective and takes much longer to establish; thus, they are not at risk of permanently compromising their vision. In some cases, diplopia disappears without medical intervention, but in other cases, the cause of the double vision may still be present. Certain people with diplopia who cannot achieve fusion and yet do not suppress may display a certain type of
spasm-like irregular movement of the eyes in the vicinity of the fixation point (see:
Horror fusionis).
Monocular 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 serious causes rarely may be behind monocular diplopia symptoms, this is much less often the case than with binocular diplopia.
Temporary Temporary binocular diplopia can be caused by
alcohol intoxication or head injuries, such as
concussion (if 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 recreationally in larger doses, the
antiepileptic drugs
phenytoin,
zonisamide and
lamotrigine, as well as the
hypnotic drug
zolpidem and the
dissociative drugs
ketamine and
dextromethorphan. Temporary diplopia can also be caused by tired or
strained eye muscles. If diplopia appears with other symptoms such as fatigue and acute or chronic pain, the patient should see an ophthalmologist immediately.
Voluntary Some people can consciously uncouple their eyes, either by overfocusing 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. Monocular diplopia may be induced in many individuals, even those with normal eyesight, with simple defocusing experiments involving fine, high-contrast lines. ==Treatment==