I am sorry to hear this as i know how painful it is to see your son going through this: This is quiet a rare disease like 1 in 50000 people. As you have mentioned it -Optic neuritis- It does have treatment but not a cure yet. Patients need to take oral or injectable steroids to decrease the inflamation of nerve cells of optic nerve (nerve for vision); As inflammation of optic nerve can lead to diminition of vision. It is quiet recurrent - I have seen patients taking steroid tablets for more than 5 years myself. You boy need to get MRI scanning done to rule out Multiple sclerosis (demyelinating disease- its like degeneration of nerve cells)  - it just doesnt happen to optic nerve cells alone - it can happen to any nerve cell in the body. But on the other hand there is nothing much to worry - these individuals are quiet as normal as others - but with steroids. Feel free to ask any query/ follow up Take care Hope it helps :)