Double vision is the perception of two images of a single object seen adjacent to each other (horizontally, vertically, or obliquely) or overlapping. Double vision is medically termed diplopia. Polyplopia is the perception of three or more images of a single object overlapping each other.

There are dozens of causes of double vision ranging from benign to life-threatening. Therefore, it is important for the doctor to carefully review the history and the examination to determine the cause and initiate appropriate treatment when necessary. Sometimes, emergency treatment is needed.

Causes of Double Vision (Diplopia)
Most causes of monocular diplopia stem from poor focusing of light by the eye. Refractive errors (myopia, hyperopia, astigmatism) are common. Dry eye (from a variety of causes such as meibomitis, Sj?gren's Syndrome, and decreased tear production following refractive surgery) can produce diplopia that varies with blinking. Cataracts (clouding of the natural lens) and posterior capsule opacification (after cataract surgery) are common in people over 60 years of age. Other conditions that interfere with proper focusing of light include corneal irregularity from swelling or scars and retinal conditions, such as epiretinal membranes. Rarely is the underlying cause a medical emergency in cases of monocular diplopia.

Treatment for Double Vision (Diplopia)
Diplopia stemming from refractive errors (Myopia, hyperopia, astigmatism) can be corrected with glasses or contact lenses. Dry eyes are treated with artificial tears, punctal plugs, warm compresses, and a variety of other treatments. Cataracts are removed with surgery, and posterior capsule opacification (after cataract surgery) is treated with laser. It is uncommon for the cause of monocular diplopia to be a medical emergency.

Binocular diplopia on the other hand can be caused by life-threatening conditions, and emergency treatment may be necessary. This is particularly the case with aneurysms, head trauma, Stroke, and other neurologic conditions. Any onset of diplopia with accompanying neurologic symptoms such as Headache, nausea, dizziness, loss of balance, etc., should be evaluated immediately.

Diplopia produced by chronic diseases (see causes above) may subside with treatment of the underlying disease. If eye muscles are engorged (such as from Graves' disease) or entrapped (as after traumatic orbital fracture), surgery of the muscles or surrounding tissue may correct the problem.

Convergence insufficiency, or inability to align the eyes when focusing on a near object, is a common benign cause of intermittent binocular diplopia when reading. It can improve with eye exercises ("pencil pushups" prescribed by the eye doctor).