Eye, Optic Nerve - Degeneration
comment:Optic nerve degeneration can result from various causes, including increased intraocular pressure, compromised vascular supply, and physical trauma (e.g., from retro-orbital bleeding procedures). Since the optic nerve is composed of the axons of retinal ganglion cells, primary lesions in the retina (especially those affecting the ganglion cell and nerve fiber layers) frequently result in concurrent optic nerve pathology, including degeneration. Since the optic nerve is an extracranial white matter tract of the brain, optic nerve degeneration can also be a "descending" change secondary to lesions in the brain. Although the extent can vary with rodent strain, optic nerve axonal degeneration and loss can also be an age-related incidental change in rats and mice. Optic nerve degeneration of uncertain etiology has also been reported as a spontaneous change in adult rats.
Optic nerve degeneration can be characterized by scattered clear vacuoles (as in Figure 1 and Figure 2 ), which often contain swollen, pale eosinophilic fragmented axons and/or myelin debris. In more chronic cases, there can be decreased numbers of axons, decreased diameter of the remaining axons, and pial septa thickening. The loss of axons may lead to decreased overall diameter of the nerve. Variable glial cell proliferation and/or macrophage infiltration may occur concurrently.
recommendation:Optic nerve degeneration should be diagnosed and assigned a severity grade. The presence of optic nerve degeneration should prompt careful examination of the retina (especially the ganglion cell and nerve fiber layers) for concurrent pathology. Associated lesions (e.g., inflammation) should be diagnosed separately.
related links:Eye, Optic Nerve - Gliosis
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