Double vision is also called diplopia, which ususally caused by two main reasons. Firstly, eye health could directly affect vision. Diplopia is a symptom of strabismus, that is to say, eyes are misaligned and could turn any direction when you have strabismus. And double vision could be occured when you have astigmatism because of the cornea is irregularly shaped. Or sudden double vision may be an indication of a serious medical condition. Thus, another possibility of casuing double vision is brain conditions, such as head injury, brain tumor, brain swelling or an aneurysm. Additionally, ocular migraines may cause not only headache but also double vision due to the changes in blood flow in the brain.
