S-cone electroretinograms in multiple evanescent white dot syndrome

Cone electroretinograms (ERGs), elicited by different color flashes under Ganzfeld conditions, were recorded from 6 patients with multiple evanescent white dot syndrome (MEWDS). All of the patients had normal color vision as determined by the Farnsworth Panel D-15 except for one who showed non-specific errors. The b-waves elicited from short wavelength sensitive (S-) cones were reduced more than the mixed long (L-) and middle (M-) wavelength sensitive cones in the affected eyes. The ratio of the S-cone b-wave amplitude of the affected eyes to that of the normal fellow eyes was significantly lower than the comparable ratio for the L- and M-cone ERG b-waves (p= 0.012). The S-cone ERGs recorded from 2 patients recovered to normal levels after their symptoms abated. These ERG results indicate that the S-cone system is more impaired than the L- and M-cone systems in the acute stage of MEWDS, and the changes in the S-cones may be reversible.