Diplopia is having double vision when only a single object is present. It most often has an ophthalmological or neurological cause. When it affects only one eye, it is called monocular diplopia. When it affects both eyes, which is more common, it is called binocular. It can be due to a lesion on the cornea, iris, or lens as in an early cataract. It can also be a sign of neurological damage to the nerves responsible for the mobility of eyes with paralysis of these nerves: a potentially serious neurological lesion is suspected. Taking certain medications such as hypnotics may also be the cause of diplopia.