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Optic nerve melanocytoma does not usually produce symptoms or grow. If they slowly grow, optic nerve melanocytoma can produce afferent pupillary defects (30%), subretinal fluid (10%), and an enlarged blind spot (75%). On fundoscopic exam, the optic disc may be swollen, atrophic, or even normal. [1] Central retinal vein occlusion may occur.
Optic nerve sheath meningiomas (ONSM) are rare benign tumors of the optic nerve. 60–70% of cases occur in middle age females, and is more common in older adults (mean age 44.7 years). It is also seen in children, but this is rare. The tumors grow from cells that surround the optic nerve, and as the tumor grows, it compresses the optic nerve.
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 edema, can lead to loss of these fibers and permanent visual impairment.
Optic gliomas are usually pilocytic tumors, and can involve the optic nerve or optic chiasm. [3] Optic gliomas are usually associated with neurofibromatosis type 1 in 30% of people with the condition. [3] Optic nerve gliomas have low mortality but extremely high prevalence of vision loss and eye-bulging exophthalmos) in children. [4]
This leads to various other symptoms including headache and a swollen optic disc. The differential diagnosis for sphenoid wing meningioma includes other types of tumors such as optic nerve sheath meningioma, cranial osteosarcoma, metastases, and also sarcoidosis. Following the physical exam, the diagnosis is confirmed with neuro-imaging.
Pressure on the part of the optic nerve known as the chiasm, which is located above the gland, leads to loss of vision on the outer side of the visual field on both sides, as this corresponds to areas on the retinas supplied by these parts of the optic nerve; it is encountered in 75% of cases. [1]
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] Edema is seen in and around the optic nerve head also ...
The nasal fibers of each optic nerve decussate (cross) across the chiasm to the contralateral side while the temporal fibers course posteriorly to form the optic tract on the ipsilateral side. This arrangement allows the left half of the visual field to end up on the right side of the brain and the right half of the visual field to locate to ...
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