This study documents the results of standardized A-scan examinations performed in 59 cases of optic nerve lesions (15 perioptic meningiomas, four gliomas, 15 acute neuritides, ten optic atrophies, five ischemic optic neuropathies, five acute central retinal vein occlusions, five traumatic optic neuropathies), as compared with 73 normal optic nerves. Analysis included the assessment of reflectivity (spike height) and nerve width (maximal diameter) with the patient fixating in primary gaze and 30 degrees of eccentric gaze; measurements were obtained from the anterior one third and posterior one third of the optic nerves. Increased nerve diameters could be distinguished as noncompressible (a negative 30 degrees test) when due to tumor, or compressible (a positive 30 degrees test) when due to increased subarachnoid fluid, as exemplified by inflammatory optic neuritis or traumatic neuropathy. Moreover, reflectivity patterns regularly differentiated meningioma (medium reflectivity) from optic glioma (low reflectivity). Neither ischemic neuropathy nor vein occlusion altered optic nerve diameter. These results indicate that echographically defined optic nerve diameter, compressibility in eccentric gaze, and reflectivity patterns can be used to effectively distinguish among causes of chronic optic atrophy (tumor vs remote neuropathy) and disc edema (tumor vs neuritis vs ischemic neuropathy).