Cone electroretinograms to blue flashes on various backgrounds

Purpose To observe the S‐cone and LM‐cone responses of the photopic electroretinogram (ERG), to study their interactions, and to define under which stimulus conditions the ERG waveform reflect the function of the S‐cone as well as the L‐ and M‐cone systems. Methods The photopic ERG was recorded from 10 control subjects in a full‐field stimulator (Diagnosys LLC, Littleton, MA). Responses were elicited with intensity series (0.004 to 1 cd*s/m2) of the blue (449 nm) stimuli on a 100 ph cd/m2 amber background (=40 sc cd/m2), as well as on a 100 ph cd/m2 green and a 40 sc cd/m2 red backgrounds. Results The S‐cone response appeared at the implicit time of 43 ms, with lower stimulus intensities on the amber, green and red backgrounds. With higher stimulus intensities (0.028 cd*s/m2), it showed with a similar implicit time, but as a second peak subsequent to the LM‐cone response (b‐wave). With a further increase in intensity (0.15 cd*s/m2), the S‐cone response passed into the i‐wave of the LM‐cone system. The LM‐cone response appeared as a double peak (first peak: 24 ms; second peak: 28 ms) on an amber background at intensities from 0.028 cd*s/m2 and above. On a green background, the first peak was more prominent, while on a red background, the second peak dominated the LM‐cone response. This pattern of double‐peak appearance might indicate that the first peak originates mostly from the L‐cone system and the second peak from the M‐cone system. Conclusion The S‐cone response can be elicited with various backgrounds as a single peak to a blue flash at lower intensities, while with brighter intensities it probably interacts with the LM‐cone system. The double peak of the LM‐cone response is an interesting finding, which might indicate selective monitoring the L‐ and M‐cone systems.