Disorders in which the Margin of the Optic Disk is Well Defined

13.4.1 Atrophy of the Optic Nerve Definition

Irreversible loss of axons in the region of the third neuron (from the retinal layer of ganglion cells to the lateral geniculate body).

Morphology and pathologic classification: Atrophy of the optic nerve is classified according to its morphology and pathogenesis. The following forms are distinguished on the basis of ophthalmoscopic findings:

❖ Primary atrophy of the optic nerve.

❖ Secondary atrophy of the optic nerve.

❖ Glaucomatous atrophy of the optic nerve.

Forms of primary atrophy of the optic nerve may be further classified according to their pathogenesis:

❖ Ascending atrophy in which the lesion is located anterior to the lamina cri-brosa in the ocular portion of the optic nerve or retina.

❖ Descending atrophy in which the lesion is located posterior to the lamina cribrosa in a retrobulbar or cranial location.

Etiology:

Etiology of primary atrophy of the optic nerve.

The most important causes are as follows:

❖ Ascending atrophy (after two to four weeks):

- Usually vascular, such as central retinal artery occlusion or anterior ischemic optic neuropathy.

❖ Descending atrophy (after four to six weeks):

- Compressive, such as from an orbital or intracranial mass or hydro-cephalus.

- Traumatic, such as avulsion, compression of the optic nerve in a fracture, or hematoma in the optic nerve sheath.

- Inflammatory, such as retrobulbar optic neuritis, arachnoiditis of the optic chiasm, or syphilis.

- Chronic abuse of low-grade tobacco and alcohol in tobacco and alcohol amblyopia.

- Lead, arsenic, or thallium.

- Methyl alcohol.

- Medications, such as ethambutol, chloramphenicol, gentamicin, isoni-azid, vincristine, penicillamine, etc.

❖ Congenital or hereditary:

- Infantile hereditary optic atrophy (an autosomal dominant disorder with slow progressive loss of visual acuity, color vision defects, and visual field defects.

- Juvenile hereditary optic atrophy (similar to the infantile form only the onset is usually later, in the second decade of life).

- Leber's optic atrophy.

- Behr's infantile recessive optic atrophy.

❖ Systemic disorders:

- Hemorrhagic anemia or pernicious anemia.

- Leukosis.

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