I think that you need to go ahead and see your vet tonight.
There are a lot of conditions that can cause retinal swelling and finally detatchment (the most common cause of sudden blindness). These include but are not limited to thyroid disorders, diabetes, liver and renal failure and a lot of other conditions, most of which are treatable. All of these are concerns in an older cat.
I know you're not going to like my answer because I can't recommend that you try to treat this at home.
I would go ahead and see the vet for an exam and to get bloodwork. At this visit, you can confirm the diagnosis or get a new one and then go from there.
You need to do this quickly because, if you wait, the retinas can detatch and then sight will be permanently lost.
If finances are a problem for you, you might want to look into www.carecredit.com. They offer financing for large and small vet bills.
Let me know if you want to discuss this more.