Thank you for the addition information. It is very helpful.
Alcoholism has a direct toxic effect on the liver. You might have heard that alcohol has a lot of "empty calories". This means calories, but not a lot of other nutrients -- vitamins and minerals. So many alcoholics have vitamin difienciency.
Nutritional deficiency can cause blindness through cataracts
or optic atrophy. Cataracts would have been seen by his eye doctors
already. Optic atrophy may be more subtle and more difficult to tell. It is a degeneration of the optic nerve (the connection between your eyes and brain). Macular degeneration is another cause, but easy to tell if advance.
I don't believe the hypothyroidism would cause his current vision problems
I recommend you ask the doctor if he as any evidence of optic atrophy. If so, no treatment is available. The key is to prevent further damange through proper diet. If there are cataracts or glaucoma, that can be treated -- but he has already be tested for this.
Remember to press the green accept button. It was a pleasure helping you with your question. Feel free to ask any addtional questions.