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However, the anterior end of the optic nerve stops abruptly at the eye. Hence the pressure is asymmetrical and this causes a pinching and protrusion of the optic nerve at its head. The fibers of the retinal ganglion cells of the optic disc become engorged and bulge anteriorly. Persistent and extensive optic nerve head swelling, or optic disc ...
The optic nerve can be damaged when exposed to direct or indirect injury. Direct optic nerve injuries are caused by trauma to the head or orbit that crosses normal tissue planes and disrupts the anatomy and function of the optic nerve; e.g., a bullet or forceps that physically injures the optic nerve.
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%.
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.
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 .
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]
The optic disc may appear normal, swollen, or hyperemic in early stages. With hyperemia, disc hemorrhages may also be present. Continued damage to the optic nerve results in the development of optic atrophy, classically seen as temporal pallor of the optic disc.
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 ...
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