Ischemic Optic Neuropathies

Posted by • June 19th, 2015

A new review article covers the diagnosis, pathophysiological features, and prognosis of ischemic optic neuropathy, a relatively common cause of visual loss in older patients, including visual loss after cardiac surgery. It must be distinguished from inflammatory optic neuritis.

ION refers to all ischemic causes of optic neuropathy. ION is classified as anterior ION or posterior ION depending on the segment of optic nerve that is affected. Anterior ION accounts for 90% of ION cases. Anterior ION and posterior ION are further categorized into nonarteritic or arteritic. The term arteritic refers to ION caused by small-vessel vasculitis, most often giant-cell arteritis.

Clinical Pearls

What is the clinical presentation of nonarteritic anterior ischemic optic neuropathy, and how is it diagnosed?

Nonarteritic anterior ION is manifested as isolated, sudden, painless, monocular vision loss with edema of the optic disc. Progressive worsening of vision over a period of a few days or a few weeks is not uncommon, presumably related to worsening ischemia in the context of a local compartment syndrome associated with the disc edema. The severity of vision loss varies from normal visual acuity with visual-field defects to profound vision loss. The diagnosis of acute nonarteritic anterior ION is primarily clinical and relies on demonstration of vision loss with a relative afferent pupillary defect and edema of the optic disc, which consists of the optic-nerve head. A crucial finding on examination is the presence of a small, crowded optic-nerve head with a small physiological cup. This small cup-to-disc ratio defines a “disc at risk.” Although this finding is difficult to see during the acute phase of nonarteritic anterior ION when the optic disc is swollen, examination of the normal eye should show a disc at risk. Imaging of the optic nerve is typically normal in patients with nonarteritic anterior ION.

Figure 1. Blood Supply to the Optic Nerve and Anatomy of the Optic-Nerve Head.

What causes nonarteritic anterior ischemic optic neuropathy, and can it be successfully treated?

Although nonarteritic anterior ION results from disease of the small vessels supplying the anterior portion of the optic nerve, its exact cause remains unknown. A disc at risk is essential for the development of nonarteritic anterior ION. Other optic-nerve anomalies resulting in crowding of the optic-nerve head, such as optic-nerve drusen and papilledema, may also confer a predisposition to nonarteritic anterior ION. The absence of a disc at risk in a patient with presumed nonarteritic anterior ION should raise the possibility of arteritic anterior ION or another cause of optic neuropathy. There is no established treatment for nonarteritic anterior ION such as there is for the arteritic type of anterior ION. Thus, the most important management concerns are distinguishing nonarteritic anterior ION from arteritic anterior ION and detecting and controlling vascular risk factors in cases of nonarteritic anter ION. Most proposed therapeutic interventions in nonarteritic anterior ION are based on the presumed mechanism and cascade of events. Although multiple therapies have been attempted, most have not been adequately studied, and animal models of nonarteritic anterior ION have emerged only in the past several years. Given the paucity of data regarding the exact pathophysiology of nonarteritic anterior ION and its treatment, the maxim “first, do no harm” is most important in the management of this devastating optic neuropathy.

Figure 2. Presumed Pathophysiology of Nonarteritic Anterior ION and Potential Treatment Strategies.

Figure 3. Nonarteritic Anterior ION in the Context of a Disc at Risk.

Morning Report Questions

Q: How do the clinical findings of posterior ischemic optic neuropathy differ from those of anterior ischemic optic neuropathy, and is the diagnostic evaluation the same for both?

A: When the posterior portion of the optic nerve is ischemic, there is no visible disc edema and the term “posterior ION” is used. Nonarteritic posterior ION is exceedingly rare, as compared with nonarteritic anterior ION. The typical presentation of nonarteritic posterior ION is isolated, painless, sudden loss of vision in one eye, with a relative afferent pupillary defect and a normal-appearing optic-nerve head. As expected with any optic neuropathy, optic-disc pallor develops 4 to 6 weeks later. The clinical diagnosis of nonarteritic posterior ION is difficult and remains a diagnosis of exclusion, with other causes of posterior optic neuropathy (e.g., inflammatory and compressive causes) ruled out by high-quality MRI of the brain and orbits with contrast and with fat suppression and by an extensive workup for underlying systemic inflammatory disorders. Giant-cell arteritis is the most common cause of posterior ION, and must be considered in every patient older than 50 years of age who has posterior ION.

Q: What clinical findings may help to distinguish arteritic from nonarteritic anterior ischemic optic neuropathy?

A: The clinical presentation of arteritic ION is similar to that of nonarteritic ION, but several “red flags” should raise clinical suspicion for arteritic ION. Systemic symptoms of giant-cell arteritis may precede visual loss by months; however, about 25% of patients with biopsy-confirmed giant-cell arteritis present with isolated ION without any systemic symptoms (so-called occult giant-cell arteritis). The degree of visual loss is often more severe in arteritic anterior ION than in nonarteritic anterior ION. In one study, 54% of the patients with arteritic anterior ION were unable to count fingers as compared with 26% of the patients with nonarteritic anterior ION. Untreated arteritic ION becomes bilateral in days to weeks in at least 50% of cases. The affected swollen optic nerve is often pale immediately in giant-cell arteritis, whereas pallor is delayed in nonarteritic anterior ION. The finding of associated retinal or choroidal ischemia in addition to ION is highly suggestive of giant-cell arteritis. Finally, a disc at risk is not necessary for arteritic anterior ION; the absence of a crowded optic disc in the second eye of a patient with anterior ION should make the diagnosis of nonarteritic anterior ION unlikely and should increase the probability of arteritic anterior ION.

One Response to “Ischemic Optic Neuropathies”

  1. higinio malave says:

    what about diabetes and sudden vision loss