Ischemic optic neuropathy can be separated into its two most common forms: arteritic anterior ischemic optic neuropathy (AAION) and nonarteritic anterior ischemic optic neuropathy (NAAION).

Infections can directly involve the optic nerve, leading to an optic neuropathy. Vision loss occurs as a result of optic nerve head swelling and often hemorrhage. Primary infection of the optic nerve may lead to exudation into the macula in a star pattern. Retinal vasculitis can also occur, causing exudation, flame hemorrhages, and ischemic cotton wool spots. This combined disorder of the optic nerve and retinal vasculature is called neuroretinitis.⁴ Inflammation as well can occur in the vitreous (vitritis), and, depending on the organism (eg, tuberculosis), choroidal lesions can be seen. Common causes of infectious optic neuropathy include Bartonella and toxoplasmosis, but syphilis, Lyme, tuberculosis, cytomegalovirus, and herpes simplex virus must also be considered. Each of these has characteristic involvement of the optic nerve, retina, and vitreous, which is beyond the scope of this chapter. However, primary optic nerve involvement can occur without retina involvement in Bartonella and syphilis. In addition, optic nerve swelling from meningitis may cause an optic perineuritis.

Optic neuritis broadly describes any inflammatory condition involving the optic nerve, although it most commonly refers to inflammation caused by a demyelinating disease. Neuromyelitis optica spectrum disorder (NMOSD) is a form of optic neuritis associated with transverse myelitis and other brain stem lesions. Symptoms include unexplained hiccups, nausea or vomiting, and diencephalic syndrome. Unfortunately, the visual prognosis is poorer in NMOSD and tends to recur, leading to severe visual impairment. Myelin oligodendrocyte glycoprotein antibody disease (MOGAD) is another more recently described demyelinating central nervous system disorder that appears to be different than MS. Its presentation, however, is similar to NMOSD, with optic neuritis, transverse myelitis, or both. Magnetic resonance imaging (MRI) findings are similar, especially involving the brainstem, but can have dramatic improvement or resolution over time. Compared to NMOSD, MOGAD patients tend to be younger, lack female predominance, can present with acute disseminated encephalomyelitis (ADEM), and have a better outcome.

Other causes that overlap in the ischemic or infiltrative category include autoimmune processes such as systemic lupus erythematous, associations with inflammatory bowel disease, sarcoidosis, and Wegener.⁵

Compressive lesions of the optic nerve can occur anywhere from behind the globe to the chiasm and optic tract. The degree and location of compression correlates with the symptoms. The most common causes include optic nerve sheath and intracranial meningioma, anterior communicating artery aneurysm, and pituitary adenoma. Other infiltrative tumors should also be considered, such as optic nerve glioma in neurofibromatosis type 1 and metastatic carcinoma. Classically, patients describe a more chronic progressive peripheral vision loss. In the cases of central fiber compression, or with an acutely expanding lesion such as compressive thyroid orbitopathy, an expanding intracranial aneurysm, or pituitary apoplexy, patients may have a more acute vision loss.