Long-term follow-up of retinitis pigmentosa patients with multifocal electroretinography

METHODS. Twenty-three patients (9 men and 14 women) with clinically defined RP were included in the study. Disease progression was monitored during a period of up to 10 years by psychophysical techniques and Ganzfeld electroretinography. In addition, ERGs were recorded with a mfERG imaging system (VERIS; Electro-Diagnostic Imaging, Inc., Redwood City, CA). The black and white stimulus consisted of 61 hexagons covering a visual field of approximately 60 degrees x 55 degrees. Responses were analyzed according to concentric ring averages. RESULTS. The progression of visual field loss for target III4e was approximately 14.5%. Using the same type of regression model, the yearly progression according to the mfERG values was found to be approximately 6% to 10% in the outer three rings. Visual acuity (median 0.8) correlated well with the amplitude of the central segment of the mfERGs, ring 5 amplitudes of the mfERG strongly correlated with the scotopic Ganzfeld ERG mixed cone-rod response amplitude. However, in advanced cases, reliable mfERG responses could still be recorded, even if the ISCEV scotopic Ganzfeld ERG was not reproducible. MfERG ring 5 amplitudes as well as the Ganzfeld ERG mixed cone-rod response amplitude showed only a mild correlation with visual field area. CONCLUSIONS. The mfERG allows long-term follow-up of disease progression in retinitis pigmentosa. It does not replace, but complements psychophysical methods and could be used as an objective outcome measure in upcoming treatment studies involving patients with advanced retinal diseases.