[Colored light stimuli in ERG for differential diagnosis of cone dystrophies]

We recorded electroretinograms (ERG) with white and color stimuli in normal persons and four patients with cone dystrophies. Kodak Wratten-filters in blue, blue-green, green, yellow and red were used for the color flashes. ERGs to all color stimuli were recorded at dark and light adapted conditions with different stimulus intensities, to 30 Hz flicker stimulation and with special filtering for oscillatory potentials. Selective blue cone-responses were obtained using strong blue flashes at a yellow background. Patients with cone dystrophies showed slightly to moderately reduced responses at dark adaptation to blue, blue-green, green and yellow stimuli. Red stimuli elicited only small responses with a markedly delayed b-wave implicit time. The light adapted recordings, flicker responses and oscillatory potentials were reduced to all color stimuli. However, differences between patients with cone dystrophies could be detected concerning the responses to red and green. In two patients the responses were reduced to the same degree to all color stimuli. Another patient had very small responses and no oscillatory potentials to red, but his responses were only moderately reduced to green. A patient with combined red-green cone and rod dystrophy had a blue cone hypersensitivity. Responses to blue and blue-green were large at all stimulus conditions, but responses to all other stimuli were much smaller. The blue cone ERG showed a prominent blue cone response. ERG recording to colored stimuli allows a separation of retinal dysfunction in patients with cone dystrophies.