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L- and M-Cone–Driven Electroretinograms in Stargardt’s Macular Dystrophy–Fundus Flavimaculatus

¹ From the Department of Experimental Ophthalmology, University Eye Hospital, Tübingen, Germany; the ² Department of Medical Biometry, University of Tübingen, Germany; and the ³ Institute of Human Genetics, Biocenter, University of Würzburg, Germany.

PURPOSE. To study the dynamics of the long (L)- and middle (M)-wavelength–sensitive cone-driven pathways and their interactions in patients with Stargardt’s macular dystrophy-fundus flavimaculatus (SMD-FF) and to correlate them with other clinical parameters and individual genotypes.

METHODS. Forty-seven patients with SMD-FF participated in the study. In addition to standard 30-Hz flicker electroretinograms (30-Hz fERG), ERG responses were measured to stimuli that modulated exclusively the L or the M cones (L/M cones) or the two simultaneously. Blood samples were screened for mutations in the 50 exons of the ABCA4 gene.

RESULTS. Patients with SMD-FF did not show a decrease in the mean L/M-cone–driven ERG sensitivity, but there was a significant increase in the interindividual variability. The mean L-/M-cone weighting ratio was normal. However, the L-cone–driven ERG was significantly phase delayed, whereas the M-cone–driven ERG was significantly phase advanced. These phase changes were significantly correlated with disease duration. The amplitude and implicit time of the standard 30-Hz fERG both correlated significantly with the L/M-cone–driven ERG sensitivity and with the phase difference between the L/M-cone–driven ERGs, indicating the complex origin of the standard 30-Hz fERG. Probable disease-associated mutations in the ABCA4 gene were found in 40 of 45 patients, suggesting that they form a genetically fairly uniform SMD-FF study group. There was no correlation between the genotype and the L/M-cone–driven ERGs.

CONCLUSIONS. The changes in L/M-cone–driven ERG sensitivity and phase possibly represent two independent disease processes. The phase changes are similar to those found in patients with retinitis pigmentosa and possibly are a general feature of retinal dystrophies.

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