الفهرس 
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Abstract
The optic nerve is most vulnerable to injury by a compressive force where it is adjacent to bone or in a confined space (eg, orbital apex, optic canal). The clinical hallmark of compressive optic neuropathy is slowly progressive vision loss. characteristic findings on clinical examination include reduced visual acuity, dyschromatopsia, a relative afferent pupillary defect, visual field defect, and optic atrophy (or edema). A delay in the diagnosis of compressive optic neuropathy is not uncommon since the vision loss is insidious, and the clinical findings may be missed or misinterpreted as a cataract, maculopathy, glaucoma, or optic neuritis.
Clinicians should consider compressive optic neuropathy in the differential diagnosis of unexplained, asymmetric visual acuity, normal or low-tension glaucoma, or visual symptoms responsive to corticosteroids. Similarly, a workup of incidentally discovered optic atrophy should include a neuroimaging study (eg, magnetic resonance imaging) to rule out a compressive lesion. The management of compressive optic neuropathy is often difficult, given the proximity of compressive lesions to critical neurovascular structures in the orbit and intracranial space. Many of the conditions causing compressive optic neuropathy are also resistant to radiotherapy at doses tolerated by the globe and anterior visual pathways. (250)
Optic disc changes
Among the numerous optic disc findings in compressive optic neuropathy are atrophy, edema, papilledema, shunt vessels, and Foster Kennedy syndrome.
1. Optic atrophy. This is the most common finding; early in the clinical course of optic nerve or chiasmal compression, the optic disc may appear normal. While some optic disc cupping may occur from causes of compressive optic neuropathy, optic disc pallor occurs out of proportion to the degree of cupping. Decreased thickness of the retinal nerve fiber layer occurs with the development of optic atrophy. (251,252)
2. Band or bowtie optic atrophy. A type of atrophy seen with chiasmal or optic tract compression in an eye with a temporal hemianopic defect (loss of decussating nasal retinal fibers). Sparing of temporal retinal fibers (and the nasal field) results in relatively normal arcuate bundles, which are located in symmetric superior and inferior wedges on the disc. Temporal fibers of the papillomacular bundle and nasal peripheral fibers are atrophic, resulting in optic atrophy in a horizontal bowtie distribution. This pattern of thinning of the retinal nerve fiber layer has been noted in vivo using scanning laser polarimetry and optical coherence tomography. (253).