Yes. Alcohol can have negative effect on optic nerve which the eyes use to focus the lens upon the retina in the eye to make an image of what we see. When retina is stimulated by alcohol, it will have congestion easily can cause the image we see out of shape.
Alcohol can interfere the intake of Vitamin in body and consume too much vitamin instead. Vitamin A is the important nutrition for retina and the lack of it can cause impaired vision. So you should persuade your father to drink less.
Yes. Drinking too much will affect the function of optic nerve, so you will find things blurry after you've drunk too much. If you often drink heavily, your vision will get decreased. To keep healthy, you should tell him to drink as little as possible.