A pattern VEP system for screening for glaucoma and other optic nerve related diseases/deficiencies. The system combines high contrast and low contrast testing. The low contrast testing allows for highly sensitive glaucoma testing and the high contrast allows for a sensitive test of the central vision. The system also includes a narrowly tailored method of rejecting corrupted data allowing the system to selectively salvage useful portions of a signal. The system also provides a method of data modeling to locate the N75-P100-N135 complex in a waveform and determine if it falls within the normal range.