Green field vision

EthambutoL The cause of its specific antitubercular action is unknown. Ethambutol is given orally. It is generally well tolerated, but may cause dose-dependent damage to the optic nerve with disturbances of vision (red/green blindness, visual field defects). 

The onset of visual loss can be sudden and dramatic, with color vision defects in the red-green or blue-yellow spectra, as well as variable field defects. In acute cases, disc edema is accompanied by sphnter hemorrhages. Retrobulbar neuritis with ethambutol can be predominantly axial, presenting with reduced visual acuity and central scotoma, or periaxial, with peripheral field defects. In non-acute tjrpes the fundi and discs appear normal (13). Visual defects can be unilateral or bilateral. 

Visual acuity was not altered in normal healthy human subjects by 10 mg. of morphine. The fields of vision for white and blue remained normal, but those for red and green were reduced (Macht and Macht, 13). However, visual thresholds were elevated to about ten times their original value by the administration of morphine to post-addicts (formerly addicts but now undergoing rehabilitation). The pupillary constriction produced by the morphine may have contributed to the elevation of the visual thresholds (Andrews, 14). 

Has distant visual acmty of at least 20/40 (SneUen) in each eye without corrective lenses or visual acmty separately corrected to 20/40 (Snellen) or better with corrective lenses, distant binocular acmty of at least 20/40 (Snellen) in both eyes with or without corrective lenses, field of vision of at least 70° in the horizontal meridian in each eye, and the ability to recognize the colors of traffic signals and devices showing standard red, green, and amber ... 

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