An effective and clinically relevant parameter for differentiating ischemic optic neuropathy (ION) and optic neuritis (ON) patients using the Visual Evoked Potentials (VEPs) has been identified. In this study, statistical analysis has been carried out on time domain parameters of the VEP waveforms recorded for ION (17 patients) and ON (35 patients) groups. The ratio of the amplitude of P100 component of affected eye to fellow eye showed no significant difference between the two groups. However, the mean P100 absolute latency component of ION patients was found to be significantly (p<0.001) shorter than that of ON patients. This parameter will help the neurologist to clearly classify the diseased patients and help them in early therapy planning. © 2005 IEEE.