Our practical clinical need for a more exact understanding of the retinal fiber projections through the chiasm is exemplified by the many so-called paradoxic visual field defects demonstrated in patients with pathologic involvement of this structure.1The most dependable information we have concerning visual fiber projections in the chiasm derives from Marchi myelin degeneration studies in the primate following experimental lesions in the retina.2-5These studies provided valuable but limited information on chiasmal anatomy; the available techniques failed to provide important detail. During the past decade an improved instrument for production of retinal lesions, the Zeiss retinal-photocoagulator, and new histologic techniques for the demonstration of axon degeneration (Nauta silver impregnation)6have opened the way for renewed attempts to unravel the complexities of the nerve fiber anatomy within the primate chiasm. We have already reported on the applications of these improved techniques in the study of visual fiber