There are several different types of diplopia, and many different causes. Sometimes, double vision can be a symptom of an serious underlying disease or condition. Double vision means that you simultaneously see two separate images of the same object. In some cases, double vision can be little more than a feint ‘ghost’ image, which is easily confused with blurred vision. Double vision can be horizontal, where the images appear side by side; vertical, where the images appear one above the other; or diagonal, where the images are both vertically and horizontally displaced from one another.

Double vision makes it difficult to see objects at any distance, and can particularly affect your spatial awareness, and therefore your ability to drive. Children with double vision may frequently cover one eye, or they may tend to squint or turn their head in an unusual way to try to see properly.