Double Vision

Double Vision

PKGhatak,MD

If we cover one eye and look at an object, we see it as one, then remove the cover and look at the same object with both eyes we still see it as one. How is it possible?

It is the coordinated movements of eye muscles turning eyes in such a way that the image is formed on the corresponding points of each retina.

Six muscles move each eye in all possible directions; the muscles, in turn, are supplied by three cranial nerves. The one called the 3^rd cranial nerve supplies all but two muscles of the same side. The remaining muscles are supplied by the 4^th and the 6^th cranial nerves. The coordinated movement controller of the 3^rd, 4^th and 6^th cranial nerves are located in the cerebral cortex of the brain and by direct connections and relays it makes the eyeballs move in a harmonious fashion and keep the visual axis parallel.

In normal people when an object is placed very close, next to the nose, both eyeballs rotate inwards the visual axes converge and the image appears as double.

Muscles of the eyes may be damaged in accidents and certain diseases like Myasthenia gravis and Graves disease of the thyroid gland. The image of the involved eye may not land on the corresponding points on the retina of the normal eye. The image produced by the involved eye is called a false image and appears on the outside edge of the image produced by the normal eye. As the object is moved gradually further away from the eye involved two images appear further and further apart.

Diabetes is the most common cause of damage to the cranial nerves besides injuries of the face and orbit in automobile accidents. Damage to the 6^th cranial nerve in particular and other cranial nerves may occur in the situation resulting in an increase in cerebrospinal fluid pressure as seen in head injury, intracranial bleeding, and brain and meningeal tumors. Enlarging brain aneurysm, tumors of the pituitary gland and meningitis may damage cranial nerves. Stroke may damage nerve centers. A migraine and decreased blood flow of the brain stem can produce intermittent double vision. Multiple Sclerosis patients may present with double vision. Alcoholic encephalopathy and inflammatory polyneuritis can cause double vision. Parkinson's disease may cause double vision when objects are placed close to the eyes.

Infection of the central part of the face may spread to the brain and may cause double vision. Immunosuppressed patients, diabetics and patients taking prednisone are venerable to certain fungal infections of nasal sinuses, which may spread to the brain and cranial nerves and may result in double vision.

Diseases affecting one eye, leaving the other one untouched, may cause double vision. In astigmatism the curvature of one cornea unevenly changes and may cause double vision, in some other conditions corneal optical property may change; a developing cataract of the eye lens similarly may produce double vision. Retinal diseases or growth behind the retina may distort the retina and may lead to double vision.

Double vision may be an important symptom of an underlying serious illness. It should never be neglected and should always be checked out by a doctor within a day or two.

 

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