Fig. 1

Schematic diagram of the retinal pathway generating the electroretinogram in response to light. The schematic diagram displays the cellular component of the retina and the retinal pathway in response to light generating the electroretinogram (ERG) waveform. Light passes through the transparent retinal layers before reaching the photoreceptor chromophores which absorb the photons. The cone photoreceptor outer segment subsequently hyperpolarises, shutting off glutamate release into the post photoreceptor synapse. This hyperpolarisation is recorded as the a-wave in the electroretinogram waveform. Glutamate has opposite effects on the ON- and OFF-bipolar cells. Decreased glutamate binding on the mGLUR6 receptor starts a cascade of signals that open the transient receptor potential cation channel, subfamily M, member 1 (TRPM1) channel which depolarises the ON-bipolar cells and increases glutamate release to the ON-ganglion cell [31]. In contrast, the OFF-bipolar cell becomes hyperpolarised by the reduction of glutamate release from the cone cell binding on the iGLUR4 receptor, resulting in decreased glutamate release toward the OFF-ganglion cell. The b-wave amplitude is the summation of ON- and OFF-bipolar cell responses. The Photopic Negative Response (PhNR) is the summation of ON- and OFF-ganglion cell responses and contributions of Müller cell potassium currents. Glu, glutamate release; red arrow pointing down means reduced; mGLUR6, metabotropic glutamate receptor 6; iGLUR4, ionotropic glutamate receptor 4. Retinal layers: OS, Outer Segment; ON, Outer Nuclear; OP, Outer Plexiform; IN, Inner Nuclear; IP, Inner Plexiform; GC, Ganglion Cell