The optic nerve is a naturally occurring electrical bundle of fibers that link the eye to the brain structures.
It can become affected by infection, inflammation or lack of oxygenation. The most common disease affecting the optic nerve is glaucoma .
This is a vast topic so we can only cover a few examples:
Optic disc edema happens when the disc is swollen. The disc can be swollen from a local process inside the eye or by accumulation of back flow pressure from the cerebrospinal fluid. When bilateral optic nerve edema is observed it is called papilledema. This is a medical emergency that can arise because of malignant high blood pressure, brain mass or brain inflammation. A specific subtype is called Pseudo Tumor Cerebri or Idiopathic Intracranial Hypertension. (IIH)
Neuroretinitis: this is constellation of signs that include disc edema. It is usually due to an infection agent such as cat-scratch disease, lyme disease, syphillis, rocky mountain spotted fever...If you are diagnosed with neuro-retinitis, your eye doctor will order some blood work to determine the disease process responsible for the problem.
Ischemic Optic Neuropathy happens when the blood flow to the optic nerve is compromised. Two subtypes exist: Non Arteric Ischemic Optic Neuropathy (NAION), usually due to chronic damage to the blood vessels that feed the optic nerve or Arteric Ischemic Optic Neuropathy, which is usually due to intense inflammation shutting down the blood supply. Namely the concern with Ischemic Optic Neuropathy is to rule out Giant Cell Arteritis or GCA. Those entities can and do create sight-threatening consequences and unfortunately permanent vision loss. If you lose vision suddenly in one eye. Do not wait, see your eye doctor immediately for an evaluation. From there he will guide you on proper management to mitigate eye damage and save the other eye.