Dr said swollen left eye optical nerve caused loss of vision in my lower left eye. after 5 months the swelling is gone and he says the damage is perma?

Time will tell: Nerve damage often is permanent , so even if the swelling is gone it certainly is possible that loss of vision will be permanent. Hopefully, the damage was mild, and you will gain some vision back, but the longer the vision problems the more likely it is permanent.

Ischemic optic nerve: You most likely had ischemic optic neuropathy, a condition in which there is a disturbance in blood flow to the optic nerve which causes the optic disk to become swollen and is associated with loss of peripheral vision. 40% of patients get some improvement in vision as the optic nerve swelling improves/resolves. Common risk factors are hypertension, diabetes and high cholesterol/lipids.