Double Vision Causes

Double vision or diplopia is a condition in which two images of the same object are seen. This eye problem can occur in both eyes or even in one eye. Diplopia in both eyes is known as binocular diplopia whereas diplopia affecting one eye is called monocular diplopia. Binocular diplopia is more common than monocular diplopia. Double vision causes include structural and functional abnormalities in the eye and the visual system. Functional problems in the visual system result in double vision in one eye whereas structural problems in the eye result in double vision in both the eyes.

Image Formation due to Double Vision

When light rays emitted from an object strikes the retina, they create signals that are carried to brain via the nerves in the eyes. These signals create the perception of seeing an image. Light rays enter the eyes through the pupil. The light rays first cross the cornea and then travel through the aqueous humor and strike the lens. Here, according to the thickness of the lens, the direction of the light rays is changed. The rays now travel through the vitreous humor and strike the retina. The rays that strike the fovea of the retina, give the perception of the object lying directly in front of the eye. Those that strike the areas around the fovea, are perceived as those above, below or on the sides of the main object.

When an object is viewed with both the eyes by a person who doesn't have any functional or structural problems with his visual system, corresponding areas of the retina in both the eyes are stimulated. Hence, a single image of the object is seen. However, when there is a structural or functional problem with the eyes or the visual system, two separate images may be perceived by the brain that causes diplopia. This is how binocular diplopia is caused. Any structural abnormality in one eye can result in monocular diplopia.

Causes of Double Vision

Diseases: Diseases are common causes behind double vision. Thyroid problems may affect the external eye muscles due to which both the eyes may not be able to point in the same direction as the object to be viewed. Diabetes may affect the nerves that aid in eye movement. Multiple sclerosis, a neurological problem that affects the central nervous system and myasthenia gravis are other causes. A blood clot behind the eye may hinder normal eye movement. These are all common binocular double vision causes.

Corneal Problems: Corneal problems are one of the common causes of diplopia in one eye. This may happen due to infection in the cornea like shingles or herpes zoster or may be the result of a complication due to LASIK surgery. The altered corneal surface distorts the direction of the light rays as they travel towards the retina. This causes diplopia in on eye. Astigmatism in which the cornea is abnormally curved causes refractive error. This is another common cause of diplopia in one eye.

Lens Problems: Lens problems like cataracts and dislocated lens are some common causes. Dislocated lens may be caused due to breaking of ligaments that hold the lens or due to a condition known as Marfan's syndrome. Although double vision in both eyes is more common than in one eye, cataracts is a common cause of monocular diplopia.

Nerve Problems: Some diseases like diabetes and multiple sclerosis cause double vision by weakening the nerves of the eyes. Other than these diseases, Guillain-Barré syndrome also affects the nerves that cause double vision.

Complications in the Brain: Aneurism in which arteries of the brain bulge can cause double vision problem. Strokes and increased pressure inside the brain due to injury are other brain problems that cause double vision. Brain tumors or cancer behind the eye may distort the image produced by the eyes. Besides all these conditions, a stroke can also be one of the causes for diplopia.

Miscellaneous: Other than all the problems discussed, strabismus is a common double vision cause in children. This could be due to a defect in the ocular muscles or it could be congenital as well. Dry eyes (lack of sufficient tears being produced) and a swelling in the eyelid that presses the front of the eye are common diplopia causes in one eye.

Vision lenses and prism therapy are some of the common double vision treatment available. However, it is important to understand the causes before a line of treatment can be adopted.