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In both types of PION, decreased blood flow leads to the death of optic nerve cells. Ischemic injury to the optic nerve causes inflammation and swelling. Because the posterior optic nerve passes through the optic canal, a bony tunnel leading to the brain, swelling in this rigid space causes compression of the optic nerve. This compression ...
Ischemic optic neuropathy (ION) is the loss of structure and function of a portion of the optic nerve due to obstruction of blood flow to the nerve (i.e. ischemia).Ischemic forms of optic neuropathy are typically classified as either anterior ischemic optic neuropathy or posterior ischemic optic neuropathy according to the part of the optic nerve that is affected.
Posterior ischemic optic neuropathy is a syndrome of sudden visual loss with optic neuropathy without initial disc swelling with subsequent development of optic atrophy. This can occur in patients who are predisposed to AAION and NAION as described above as well as those who had cardiac and spine surgery or serious episodes of hypotension.
The exact mechanism of optic nerve ischemia in these cases remains unclear, but contributing factors may include hypotension, anemia, hypoxia, and changes in the autoregulation of optic nerve arterial blood flow. The incidence of ischemic optic neuropathy leading to vision loss following general surgeries ranges between 0.1% and 0.002%. [15] [16]
Unilateral or bilateral optic disc edema may occur. The exact etiology, pathogenesis and mechanism of the disc edema is unknown. [ 1 ] [ 2 ] Theories suggest that the dis edema is due to retinal vascular leakage into and surrounding the optic nerve and disruption of axoplasmic flow resulting from microvascular disease of the optic nerve head. [ 2 ]
Nonarteritic anterior ischemic optic neuropathy is an isolated white-matter stroke of the optic nerve (ON). NAION is the most common cause of sudden optic nerve-related vision loss, affecting more than 10,000 Americans every year, often bilaterally.
The most common cause is multiple sclerosis (MS) or ischemic optic neuropathy due to thrombosis or embolism of the vessel that supplies the optic nerve. [ 13 ] [ 14 ] Up to 50% of patients with MS will develop an episode of optic neuritis, and 20–30% of the time optic neuritis is the presenting sign of MS .
Anterior or retrobulbar ischemic optic neuropathy not associated with pain. Chronic progressive vision loss that mimics a compressive lesion. The main features that differentiate AON from the more common typical demyelinating optic neuritis is the poor recovery of vision and the chronic or recurrent or bilateral course of AON. [2]
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