[Multi-flash ERG in cone dystrophies and cone-rod dystrophies]

Scotopic electroretinograms elicited with a multiple flash procedure were reported to be helpful in diagnosis of macular diseases. To evaluate the contribution of rods and cones to the recovery of light responses as recorded with this technique we performed a triple flash ERG procedure in patients with cone dystrophies and cone-rod dystrophies.

In 8 patients with cone dystrophy and 8 patients with cone-rod dystrophy and also in 18 healthy controls we recorded a standard ERG and the scotopic triple flash ERG with intensities between 0.01 and 0.2 cds/m2. Interflash intervals were adjusted at 140, 280, and 560 ms. Responses of the standard ERG were analysed as well as b-wave amplitudes at the short dark interval (140 ms) and the longer dark interval (280 ms). These responses were compared to responses after a long interflash interval (560 ms). Using a theoretical model parameters of b-wave recovery were determined and compared between the groups.

In cone dystrophies responses of the scotopic triple flash ERG and the b-wave recovery parameters were normal whereas in combined dystrophies the triple flash responses were abnormal and the recovery data were pathologic.

Cones did neither contribute to responses obtained with the multiple flash technique nor did they affect b-wave recovery as tested with this technique. Pathologic responses as described earlier with this technique in macular diseases could only be attributed to pathomechanisms globally affecting the rod system, e.g. dysfunction of retinal energy metabolism.