97th DOG Annual Meeting 1999
V674
ROD PHOTORECEPTOR FUNCTION IN RETINAL DYSTROPHIES: INVESTIGATIONS WITH BRIGHT-FLASH-ELECTRORETINOGRAPHY (ERG)
E. Apfelstedt-Sylla, T. Usui, D. Besch, E. Zrenner
The mathematical model provided by Hood and Birch (1) allows an improved description of rod photoreceptor function,derived from parameters of the ERG a-Wave. We established this method in our clinical routine in order to determine it's value for clinical testing of patients with hereditary retinal dystrophies.
Methods: Scotopic and photopic ERG responses were elecited by bright white Ganzfeld stimuli with increasing flash intensity (3.49-4.54 log. trolandsec.). "Pure" rod responses were obtained by subtracting the photopic from the scotopic waveforms. By evaluating the leading edges of the ERG a-waves with the Hood-Birch model, the parameters RmP3 (maximal amplitude) and S (Sensitivity) of the rod PIII process were estimated.
Results: Patients with different forms of retinal dystrophies were evaluated. In patients with retinitis pigmentosa (RP) , reduced RmP3 values were always found, but S values ranged form normal to subnormal. One x-linked RP carrier female with a normal standard ERG had a subnormal RmP3 on bright-flash ERG. In patients with different forms of macular dystrophies including patients with M. Stargardt, decreases of both RmP3 and S were revealed.
Conclusion: Evaluation of bright-flash ERG waveforms with the Hood-Birch model may be a useful tool for establishing clinical diagnoses and
for evaluating retinal function in patients with inherited retinal dystrophies
1) DC Hood, DG Birch: Vis. Neurosci 5 (1990) 379-387
Univ.-Augenklinik, Abt. für Pathophysiologie des Sehens und Neuro-Ophthalmologie, Schleichstraße 12, D-72076 Tübingen
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