Transient and steady-state electroretinograms and visual evoked potentials to pattern and uniform-field stimulation in humans

I recorded simultaneously transient and steady-state electroretinograms (ERGs) and visual evoked potentials (VEPs) in response to pattern and uniform-field stimulation in 21 normal subjects, in order to study their physiological characteristics. ERGs and VEPs to pattern stimulation (P-ERGs and P-VEPs, respectively) showed different physiological features from those to uniform-field stimulation (U-ERGs and U-VEPs, respectively). With transient stimulation at a rate of 1Hz for both pattern and uniform-field stimulation, the b-wave latency of U-ERG tended to be shorter than that of P-ERG, while the P100 latency of P-VEP was significantly shorter than that of U-VEP. With steady-state stimulation at a rate of 4Hz for pattern stimulation and of 8Hz for uniform-field stimulation, the phase analysis revealed the first (1F) and the second (2F) harmonics as stable components for the U-ERG and U-VEP, while only 2F harmonic was a stable component for the P-ERG and P-VEP. The phase values of these components were different each other, and the maximal amplitude of the ERGs was shown by the 1F of U-ERG while that of the VEPs was shown by the 2F of P-VEP. These results suggest that the pattern and uniform-field stimulation allows us to separate pattern (contrast)-specific responses from luminance-specific responses both in ERGs and VEPs. Four patients with optic atrophy showed normal U-ERG while all of them showed abnormal P-ERG, U-VEP and P-VEP except one, who showed normal U-VEP. P-ERGs and P-VEPs may offer the information about the proximal inner retinal layer (or the ganglion cells) and the contrast channel of the visual cortex. U-ERGs and U-VEPs may be useful in evaluating the functions of the preganglionic cell activity in the retina and the luminance channel of the visual cortex. Therefore, simultaneous recording of ERGs and VEPs to pattern and uniform-field stimulation under both transient and steady-state conditions increase the diagnostic value of electrophysiologic testing in the visual pathways.