Double vision refers to when a person experiences seeing two images of one object. It may occur when either one (monocular diplopia) or both eyes (binocular diplopia) are open. If one eye is closed, binocular double vision will disappear. Double vision can present with additional symptoms, such as eye pain, bulging eye, or muscle weakness, depending on the root cause of double vision.
Monocular double vision occurs as light is distorted as it travels through the eye to the retina. Unlike its name, there could be more than two images present in double vision, with one image presenting in normal clarity, while the other image appears inferior in quality. The most common causes of monocular double vision are clouding of the eye lens (cataracts), problems with the shape of the cornea, or an uncorrected refractive error such as astigmatism.
Binocular double vision, on the other hand, suggest that both eyes are not pointing at the same object, often due to a misalignment between the eyes. In some cases, binocular double vision will become apparent only when moving eyes to an extreme point in a certain direction. For example, if they are turned too far to the right, left, up, or down. Binocular double vision can be caused by paralysis of a nerve that controls the muscles that move the eyes, a mechanical blockage of eye movement, or myasthenia gravis.
Double vision, especially if sudden or acute, is a concerning symptom that should prompt patients to seek care from an optometrist immediately. Double vision indicates an imbalance in the visual system that has to be properly diagnosed. In some cases, simple eyeglasses can help fix the issue and no further treatment is required. However, sudden double vision can be indicative of more serious and potentially life-threatening conditions such as strokes, aneurysms or neurological disorders.
If you are experiencing double vision, visit your optometrist immediately for a proper work-up.