To determine the origin of oscillatory potentials (OPs), binocular electroretinogram (ERG) recordings were performed under light and dark adaptation on adult healthy C57BL/6J mice. In the experimental group, 1 μL of PBS was injected into the left eye, while the right eye was injected with 1 μL of PBS containing different agents: APB, GABA, Bicuculline, TPMPA, Glutamate, DNQX, Glycine, Strychnine, or HEPES. The OP response depends on the type of photoreceptors involved, showing their maximum response amplitude in the ERG induced by mixed rod/cone stimulation. The oscillatory components of the OPs were affected by the injected agents, with some drugs inducing the complete abolition of oscillations (APB, GABA, Glutamate, or DNQX), whereas other drugs merely reduced the oscillatory amplitudes (Bicuculline, Glycine, Strychnine, or HEPES) or did not even affect the oscillations (TPMPA). Assuming that rod bipolar cells (RBC) express metabotropic Glutamate receptors, GABA_A, GABA_C, and Glycine receptors and that they release glutamate mainly on Glycinergic AII amacrine cells and GABAergic A17 amacrine cells, which are differently affected by the mentioned drugs, we propose that RBC-AII/A17 reciprocal synapses are responsible for the OP generation in the ERG recordings in the mice. We conclude that the reciprocal synapses between RBC and AII/A17 are the basis of the ERG OP oscillations of the light response, and this fact must be taken into consideration in any ERG test that shows a decrease in the OPs’ amplitude.

Some discrepancies have been observed in the diagnostic efficacy of multifocal visual evoked potential (mfVEP) when evaluating visual field defects in glaucoma patients. Therefore, we evaluated the diagnostic precision of the mfVEP in glaucoma to find its best diagnostic indicator. A systematic review and meta-analysis of quantitative studies published up to 1 April 2021 was performed. The methodological quality of the included articles was assessed. Publication bias analysis and heterogeneity tests were performed. The sensitivity, specificity and diagnostic odds ratio were calculated. The area under the curve (AUC) was calculated using the summary of receiver operating characteristics curve. Six studies with a total of 241 patients were included according to the inclusion and exclusion criteria. The AUC was 0.98. There was no evidence of publication bias or threshold effect. The pooled sensitivity and pooled specificity of the mfVEP amplitude for detection of visual field defects in all studies was 0.93 and 0.89, respectively. The positive and negative likelihood ratios of mfVEP amplitude were 6.56 and 0.08, respectively. The amplitude of mfVEP showed a good diagnostic precision in the prediction of visual field defects. Interocular mfVEP amplitude analysis can be a good diagnostic indicator for visual field study.

Between the cornea and the posterior pole of the eye, there is a transepithelial potential capable of being registered through an electrooculogram (EOG). It is questionable whether electrooculographic responses are similar in both eyes despite ocular dominance in human beings. We studied the effect of different electrooculographic stimulation parameters, in terms of directionality, linear and angular velocity, contrast, and state of adaptation to light/dark, that may induce possible interocular differences in visual function. The study was carried out with electroencephalography-type surface electrodes placed in the medial, lateral, superior, and inferior positions of both human eyes to record the eye movements. We found a greater amplitude of the EOG response in the left eye than to the right eye for light bars moving from right to left (p < 0.01; t-test). The EOG response amplitude was similar in both eyes for light bars moving in vertical directions, but greater than horizontal or rotational stimuli. We conclude that vertical stimuli should be used for EOG functional evaluation of eye movements, since horizontal stimuli generate significant interocular differences.

The signaling of flash visual evoked potential (fVEP) derives from the retina, but how retinal activity influences fVEP remains unclear. This work aimed to decipher the specific retinal kinetic contributions to fVEP response. Monocular and simultaneous recordings of flash VEP and electroretinogram were performed. Healthy and adult mice C57BL/6J were used. The right eye was injected intravitreally with 1 μL of PBS containing 25 mM APB, 10 mM Bicuculline, 30 mM DNQX, 100 mM Glutamate, 100 mM GABA, 5 mM TPMPA, or 25 mM HEPES. The left eye was injected with 1 μL of PBS and then wore an opaque patch. The amplitude and latency of fVEP were analyzed in detail. In the control group, at light intensity ≤0.1 cd·s/m², four robust components of the fVEP recordings, N1, P1, N2, and P2, were identified in dark adaptation conditions. After administration reagents, N1 and P1 components were abolished by APB, Bicuculline, DNQX or TPMPA, but were preserved by GABA/Glutamate or HEPES. Notably, N2 and P2 components were always kept. The latency and amplitude of fVEP were shown to be stimulus-dependent. Nevertheless, the amplitude showed greater inter-individual variability than latency. N1 and P1 components are strongly related to rod photoreceptor activity and/or the level of horizontal cell excitation. Latency, rather than fVEP amplitude, could be a good biomarker for clinical and diagnostic purposes, particularly the P2 latency in the rod-driven scotopic response.