Yes, sometimes, i will feel double vision especially when i have headaches. Usually, temporary double vision can be caused by too much alcohol consumed. But it is temporarily, your can recover your vision after you wake up from alcohol. This is bot a big problems. Also, migraine headaches, head trauma or stroke, brain tumor can also cause double vision. If above all not the causes of your father's blurred vision, you'd better suggest him go to see doctor for sake of his health.
Well, first, I have to tell you that there are many reasons which can cause the double vision, such as alcohol, stress, and injury to the eyes. So for your father's situation, it may caused by alcohol. Maybe you can check it with your father. And as we know that double vision is a condition in which, whenever you look at any object, you see its two images rather than one. And according to some experts, it is totally different from blurred vision, in which you see a single blurry and unclear image of an object. For the side effects, you should know that when suffering from double vision, it will severely harm decision-making capacity and quite often. And what is more, if you insist on driving, put others as well as yours life at risk. So just be careful about it.
The temporary double vision can be caused by the problems in any part of the vision system such as the problems in cornea, lenses, muscle, nerve and brain. If there is something wrong in your cornea, only one of your eyes is likely to see double vision. This is because that the surface of your eye is damaged thus the incoming light is distorted, which leads to double vision. The damage may be the result of cornea infection and a rare complication of LASIK surgery. Cataract, which is the problem in lenses, will distort the images from both eyes and cause double vision. Muscle problems such as myasthenia gravis and grave disease are the possible cause of double vision. Besides, when you are suffering from multiple sclerosis, guillain-barre syndrome, uncontrolled diabetes, stroke and brain tumors, you will see double vision.