97th DOG Annual Meeting 1999
K671
ERG RECORDINGS TO CONE ISOLATING STIMULI IN PATIENTS WITH BEST'S DISEASE
H. P. N. Scholl, J. Kremers, E. Apfelstedt-Sylla, E. Zrenner
Purpose: To study the amplitudes and dynamics of the long- (L-) and middle-wavelength-sensitive (M-) cone pathways in patients with Best's disease, we measured ERG response thresholds to stimuli, which modulated the two cone types in a predefined manner.
Methods: 29 normal subjects with trichromatic vision and 5 patients with Best's disease participated in the study. The diagnosis was based on a full clinical evaluation including standard electroretinography and standard electrooculography. The stimuli (30 Hz flicker and 66 cd/m² mean luminance precluding rod input) were presented on a computer controlled monitor. The excitation in each cone type by the monitor phosphors was calculated from the phosphor emission spectra and the cone fundamentals. We measured the thresholds to stimuli which modulated exclusively the L- or the M-cones or the two in various combinations (both in phase and in counter-phase). S-cones were not modulated. The method has been reported recently (1).
Results: We were able to describe the data of the normal subjects and the patients with a vector addition model in which the amplitudes and the phases of the signals originating in the L- and M-cones are taken into account. Amplitudes to in phase modulation of L- and M-cones were supernormal in patients with Best's disease (mean=47.16 µV) compared to those of the normal subjects (mean=33.36 µV). This difference was significant (p<0.005, unpaired t-test). To give an estimation of the overall sensitivity in the L-M-cone space, we determined the point where the thresholds are minimal (the sensitivity is maximal). For the control group, the mean maximal sensitivity in the L-M-cone space was 0.3196, and for the Best's disease patients 0.5208. Also this difference was significant (p<10-5, unpaired t-test). The mean ERG-phase to L-cone modulation of the Best's disease patients was not significantly different (mean=-374.49 deg) compared to the normals (mean=-376.13 deg). The response phases to M-cone modulation, however, were significantly advanced (p<0.005, unpaired t-test) in patients with Best's disease (mean=-311.62 deg) com-pared to the normal subjects (mean=-359.43 deg).
Conclusions: In Best's disease, a supernormal sensitivitity in the L-M-cone space of the ERG responses can be observed. The pathophysiological mechanism which leads to this hypernormal sensitivity remains questionable. This is also true for the differential temporal changes of the M- and L-cone ERG responses in Best's disease.
1. J. Kremers, T. Usui, H.P.N. Scholl, and L.T. Sharpe: Invest Ophthalmol Vis Sci 1999; 40(5), in press.
Universtity Eye Clinic, Tübingen
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