There are two types of “diplopia” (double vision). “Binocular diplopia” is present only when both eyes are open and disappears if either eye is closed. This type of diplopia is caused by problems with the extraocular muscles that control the eyeballs or the nerves that signal these muscles. The two most common causes of binocular diplopia in people over the age of 50 are thyroid conditions and cranial nerve damage. “Monocular diplopia” is present with both eyes open, but persists when the problematic eye is open and the other eye is closed. Monocular diplopia is not caused by misalignment, but by conditions such as astigmatism, dry eye, and some retinal problems or certain cataracts. To determine whether your double vision is monocular or binocular, your doctor will ask you to cover one eye and then the other. If you have monocular diplopia, your doctor will evaluate you for conditions, such as cataracts, that could be causing the problem. If the problem is binocular and there has been no facial trauma, then your doctor will want ask if you have diabetes, Graves' disease or neurological disorders.
Double vision involves seeing two distinct images of a single object and is not the same as blurry vision.