Optic neuropathy

Refers to damage of the optic nerve of whatever cause.

The most common optic neuropathy in young individuals is inflammatory optic neuritis.

Ischemic optic neuropathy is the result of vascular insufficiency and not of inflammation.

Ischemic optic neuropathy refers to all ischemic causes of optic neuropathy and are considered equivalent to a stroke of the optic nerve.

Ischemic optic neuropathy is the most common acute optic neuropathy in older individuals, with an annual incidence estimated 2.3-10.2 cases per hundred thousand persons 50 years of age or older.

Ischemic optic neuropathy is classified as anterior or posterior depending on the segment of the optic nerve that is affected.

Interior ischemic optic neuropathy accounts for 90% of cases of ischemic optic neuropathy.

Ischemic optic neuropathy can also be categorized into non-artertic versus arteritis relecting the presence or absence of small vessel vasculitis.

The most common small vessel vasculitis affecting the optic nerve is giant cell arteritis.

Involvement of the anterior portion of the optic nerve with small blood vessel disease results in hypo perfusion and ischemia of the anterior optic nerve.

Nonarteritic anterior optic ischemia neuropathy is associated with progressive worsening of vision from a few days to a few weeks and it relates to worsening ischemia in the context of a local compartment syndrome associated with disc edema.

Nonarteritic anterior optic ischemia neuropathy is diagnosed on a clinical basis and relies on demonstration of vision loss with an afferent pupillary defect and edema of the optic disc.

Nonarteritic anterior ischemic optic neuropathy results from a disease of the small vessels supplying the anterior portion of the optic nerve.

Nonarteritic anterior optic ischemia neuropathy cause is unknown.

A pre-disposition to the development of nonarteritic anterior optic ischemia neuropathy occurs with crowding of the optic nerve head such as is present with optic nerve drusen and papilledema.

Systemic disorders associated with nonarteritic anterior optic ischemia neuropathy include:hypertension in 50% of patients, and diabetes and 25% of patients.

Other disorders associated with nonarteritic anterior optic ischemia neuropathy hypercholesterolemia, stroke, tobacco use, coronary artery disease, and obstructive sleep apnea.

On retinal examination the optic nerve head is small, with the small physiological cup and cup-to-disk ratio.

Disc edema resolves over a period of 6-11 weeks and than disc pallor develops.

In nonarteritic anterior optic ischemia neuropathy vision loss varies from normal visual acuity to profound vision loss.

Permanent visual impairment persists in nearly all patients with nonarteritic anterior optic ischemia neuropathy.

In patients with nonarteritic anterior optic ischemia neuropathy imaging studies are typically normal.

Contrast enhanced MRI of the orbits is useful to rule that a compressive opttic neuropathy or inflammatory optic neuritis when diagnosis is uncertain.

Inflammatory optic neuritis presents in second to third decades.

Inflammatory optic neuritis patients present with no pain on eye movement, and no systemic symptoms.

It is important to rule out inflammatory optic neuritis in patients with acute optic neuropathy is required.

Hypercoaguloble state associated, in rare cases, with nonarteritic anterior ischemic optic neuropathy.

Prothrombotic factors should be evaluated when the patient has anterior ischemic anterior optic neuropathy and is young without vascular risk factors, bilateral simultaneous disease, recurrent nonarteritic ischemic optic neuropathy in the same eye, familial non-arteritic anterior ischemic optic neuropathy, history of thrombophilia and absence of a disc at risk.

Patients with acute hemorrhage and anemia with the systemic hypotension may experience unilateral or bilateral non-arteritis anterior ischemic optic neuropathy.

The presence of pain upon eye movement and subsequent improvement of vision suggest an inflammatory optic neuropathy rather than anterior ischemic optic neuropathy, whereas acute, painless visual loss suggests anterior optic neuropathy.

Hallmark of a unilateral optic neuropathy is the relative afferent pupillary defect identified by The Swinging flashlight test, during which light is alternately directed towards each pupil: when light is shined into the unaffected eye both pupils constrict normally and where it is swung to the affected by both pupils should stay constricted.

Dilation of both pupils when the light is swung to the affected eye indicates a relative afferent pupillary defect and strongly suggests an optic neuropathy on that side.

MRI of the orbit is often the most helpful diagnostic tests and suspected optic nerve disorders and can distinguish between inflammatory, ischemic, and neoplastic causes.

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