What causes double vision?

Muscle imbalance: The most common cause is muscle imbalance between the eyes. If this is the cause then covering each eye will eliminate the double vision. If you cover each eye and it is still blurry, you most likely need glasses. An eye care professional can correct these problems.

Mono vs binocular...: One way to test yourself: cover either eye with your hand. If the double vision is still present with one eye occluded, then this is "monocular diplopia" and rarely neurologically threatening. Most causes of monocular diplopia are optical: astigmatism, cataracts, macular pucker etc. However, if the double vision disappears with either eye covered, this is potentially more serious.

Age related?: Myasthenia gravis, multiple sclerosis, brain tumors, strokes, all can cause problem later in life. Early on, children can have strabismus, and facial trauma, especially an orbital fracture can cause double vision.

Double vision: Double vision can be due to an optical problem of the eye such as uncorrected astigmatism, or due to an eye alignment issue which can be caused by many problem including cranial nerve palsied, myasthenia, or a problem in the orbit such as thyroid eye disease or an orbital mass. Seeing an eye doctor can help to distinguish between these possible causes.