There are vitamin pills out there that stress having things like lutein which is believed to be protective against macular degeneration.

If someone's vision is bad, especially suddenly bad, they should be seen at a hospital. Sudden changes in vision can mean stroke, tumour, glaucoma, dangerously high blood pressure and other pretty serious things.

Please see a doctor at least, an eye doctor if possible, and get a second opinion if you aren't happy with what's going on.

If low carbing were the cause, there would be more people having it.