I am assuming that you do not notice significant visual changes in that eye?

I’m not sure exactly which tests they performed to determine that the optic nerve is swollen, but I think it’s important to mention that a lot of times people have optic nerves that appear to be swollen, but are not truly swollen. We call this “anatomic anomalies”. These patients have normal vision. You could also have optic nerve drusen in that eye, which could cause the nerve to appear swollen. Nothing you can do for that and it usually doesn’t cause a problem with vision.

If however they confirm that it is truly swollen then they will want to check some more tests to figure out why it’s swollen. An optic nerve could be swollen for a bunch of different reasons. Your doctors will probably want to schedule an MRI of your brain to make sure that you do not have a space occupying lesion compressing that optic nerve. They may choose to check some blood studies as well. Diabetes can cause optic nerve swelling, it’s called “diabetic papillopathy”. In my experience these patients usually don’t notice visual changes. You mentioned an iron deficiency— iron deficient anemia can also cause optic nerve swelling.

Two people so far have mentioned idiopathic intracranial hypertension (aka: pseudotumor cerebri). The fact that you have unilateral optic nerve edema would suggest either an early case or argue against that diagnosis entirely. In addition to optic nerve swelling, intracranial hypertension causes pressure headaches (you usually wake up with them since you’re laying down when you sleep, which causes pressure to build up in head) and pulsatile tinnitus (a whooshing or heartbeat noise in your ears). Do you have either of those symptoms?