Human visual-evoked potentials (VEPs) from upper and lower hemifield stimulation are thought to reflect the anatomical and functional differences between the hemiretinas and corresponding visual pathways. Conflicting results have, however, been reported in topographic studies on the putative cortical generators. We have estimated by automatic perimetry (Octopus 2000R, Program 32) and compared the sensitivity thresholds of lower and upper hemifields of the retina in 12 healthy subjects with no history or evidence of visual or neurological diseases. A visual P3 that is linked to cognitive function was recorded in an odd-ball paradigm with presentation of high-contrast checkerboards at two different spatial frequencies at 20 degrees eccentricity in each hemifield. VEP and P3 were recorded at O1 and O2 and at Cz according to the 10/20 international system. Lower sensitivity thresholds were found, and higher VEP and event-related potential (ERP) amplitude values were obtained when stimulating the lower, compared with the upper, visual hemifield. The results are consistent with previous findings and anatomical and physiological evidence in animals and man. Interactions between perceptive process in the visual system and higher cognitive functions are a possible explanation for this finding.

The flash induced electroretinogram (ERG) and early receptor potential (ERP) were recorded in a population of patients with definite diagnosis of retinitis pigmentosa in the context of a study protocol including a complete diagnostic screening. ERPs were evoked by full-field 20-joule stimuli (5 stimuli at 10 min of interval in dark adaptation); recording was by skin electrodes positioned at the inferior orbital margin; amplifiers were set at 10–10,000 Hz. The flash ERG was absent or markedly abnormal in all cases, even at an early stage of development of the retinitis, while ERPs (with a normal morphology, latency of the R₁·component increased and a reduced amplitude compared to normal controls) could be identified unambiguously in all cases. The amplitude reduction was highly correlated with the severity of the disease as determined by kinetic perimetry and fluorangiography.