The health of the optic nerve in glaucoma can be evaluated by examination of the retinal nerve fiber layer with red free illumination. Retinal nerve fiber layer defects have been shown in some studies to precede enlargement of optic cupping and visual field defects in glaucoma patients. Detection of glaucomatous damage at an earlier stage in the disease may prevent subsequent visual field loss. Retinal nerve fiber layer evaluation may give important information in the management and treatment of glaucoma patients.