Longitudinal optic nerve sections were stained with antineurofilament antibody, and areas of axonal staining were quantified as described (11) . Briefly, 3 photographs were taken at 40Â magnification of each stained nerve at predefined locations (one each of the proximal, central, and distal portion of the nerve) covering a total area of 38,500 Km 2 of each nerve. The amount of tissue within this area that stained positively for neurofilament was calculated using ImagePro Plus 6.0 (Media Cybernetics, Silver Spring, MD) software. Data shown represent the cumulative area of positive staining/nerve.