Amir Norouzpour - Department of Ophthalmology, Birjand University of Medical Sciences, Birjand
Seyyedeh Tannaz Seyyedin Ghannad - Department of Ophthalmology, Birjand University of Medical Sciences, Birjand

Purpose: Steady-State Visual Evoked Potential (SSVEP) could be used in differential diagnosis of optic neuropathies when stimulus parameters such as spatial frequency is varied. Methods: In this study, we varied the stimulus spatial frequency. The amplitude and phase of the SSVEP signal as a function of spatial frequency were compared in patients with optic neuritis with normal individuals. All patients had minimal clinical evidence of optic nerve damage when tested. A square-wave grating of 80% contrast waspresented at 8 Hz frequency in an on-off pattern, and it was simultaneously swept in spatial frequency every one second from 2 to 30 cpd. SSVEP amplitude and phase as a function of spatial frequency were measured as the average of ten 10-s sweeps. Results: We have developed an electronic spatial frequency sweep technique for electrophysiological assessment of visual acuity and pattern vision in patients with optic neuritis. The technique allows an accurate and reliable measurement of SSVEPs to a full range of spatial frequencies in just 10 seconds. Because the measurements are so rapid, the technique suggests several new improvements in the assessment ofvisualfunction. The phase was different in patients with optic neuritis when compared to normal individuals. Spatial frequencies of 5 through 10 cpd provided the highest amplitude. Conclusion: This study could provide insights into the optimal parameters of the visual stimulus for differential diagnosis of optic neuritis. Variants of the procedure are also appropriate for sequential assessment of therapeutic conditions.