Spatial localization of retinal anomalies in regular cannabis users: The relevance of the multifocal electroretinogram

Widely used in industrialized countries, cannabis is a neuromodulator substance. The cannabinoid system is present at critical stages of retinal processing. We have recently shown a delay in bipolar and ganglion cell responses in reg- ular cannabis users, as observed using flash (fERG) and pattern (PERG) electroretinogram. Although the results ob- tained during these tests provide information about global retinal responses, they do not give any indication about the spatial localization of the anomalies that were detected. The latter may be analyzed, however, by means of mul- tifocal electroretinogram (mfERG). We recorded the mfERG responses in 49 regular cannabis users and 21 healthy subjects. The amplitudes and implicit times of the mfERG N1, P1 and N2 waves were recorded. The results showed that in regular cannabis users: in the b2? region, a signi ficant increase in the N2 implicit time (p = 0.037); in the 2-5? region, a signi ficant increase in the N2 (p = 0.018) and P1 (p = 0.046) implicit times; in the 5-10? region, a signi ficant increase in the P1 (p = 0.006) and N1 (p = 0.034) implicit times; and in the 10-15? region, a signi ficant increase in the P1 implicit time (p = 0.014). An isolated decrease in the N1 amplitude in the 2-5? region (p = 0.044) was also found. This indicates that there is a delay in the transmission of visual information from the central retina to the near periphery in cannabis users suggesting potential alterations in precise and color vision.