Optic Atrophy.

BASIC CONSIDERATIONS Optic atrophy is a misleading term which, embedded by tradition and usage, resists precise definition. It is used when there is excessive pallor of the optic disc and is thus a physical sign and not a diagnosis. Since there are many causes of optic pallor, the term is usually reserved for those cases in which there is associated visual defect, either of fields or acuity, indicating a degeneration of the fibres of the optic nerve. This definition is not satisfactory since not only may visual acuity be normal in spite of optic pallor, but degeneration of the optic nerve can be sufficient to cause diminished visual function but without optic pallor, e.g., in traumatic lesions of the nerve, blindness being immediate but pallor not developing for perhaps three weeks. Pallor is thus not the only criterion of optic atrophy and to be certain of degeneration of the optic nerve the following are also necessary:-1. Diminished visual acuity. 2. Visual field changes. 3. Recession of the disc. When there is doubt as to whether a disc is pathologically pale the knowledge of diminished visual function is often used to decide on the presence of optic atrophy.