I think you should both have a homocysteine test. This will show if you are low in 3 B vitamins that convert homocysteine to SAM.

Low B12 is usually the culprit. But also B6 and folate are needed for this conversion.

High homocysteine inflames the insides of blood vessels and can lead to blood clots. It can show up first in the eyes, either the optic nerve or retina.

Optic neuritis can also be due to low B12 levels. Get a blood test for this, and you should be at 400 pg/ml minimum. Some lab ranges still go below this and don't flag the results as LOW when they are. So ask for the numbers on your tests, always.

Low B12 is pretty common and can be caused by being vegan and also using metformin RX or acid lowering drugs for heartburn.

If you decide to use a B12 supplement, choose methylcobalamin, the active form of B12. There is a rare, genetic defect some people inherit
that cannot convert cyanocobalamin to methyl form. It is called Leber's optical neuritis. So using the commonly prescribed form, cyano, may further damage the eyes if you have this defect.