What does diplopia mean?
Diplopia means double vision.
It's usually caused by a misalignment between the two eyes when the image of the object you are looking at falls on different areas of the retina in each eye. The object is perceived as being in two different places and is therefore seen as double.
However, it can also be caused by a structural problem in one eye, such as a cataract, leading to diplopia in one eye only.