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Mirella T. Barboni, Balázs V. Nagy, Ana Laura A. Moura, Francisco M. Damico, Marcelo F. Costa, Jan Kremers, Dora F. Ventura; On and Off ERGs in Duchenne Muscular Dystrophy Patients with Deletion of Dystrophin Isoform Dp260. Invest. Ophthalmol. Vis. Sci. 2011;52(14):3513.
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Dystrophin is required for normal electrophysiology of the retina. However its specific function is not yet well established, its absence may affect ON and OFF pathways differently. This study investigated ON and OFF pathways in Duchenne muscular dystrophy (DMD) patients using full field ERG to evaluate possible asymmetric retinal alterations associated with the deletion of the dystrophin retinal isoform Dp260.
ERGs were obtained from one dilated eye of eight DMD patients (mean age = 17 ± 5 years) who underwent previous ophthalmologic examination. 4 Hz sawtooth (rapid-ON and rapid-OFF) luminance modulation of white LEDs was used at mesopic (1 cd/m²) and photopic (250 cd/m²) conditions. In addition, standard flash ERGs were measured at dark-adapted (0.09 cd/m²) and bright-adapted (28 cd/m²) conditions. The analysis was carried out in the time domain in which amplitude and implicit time of the 1st negative and the 1st positive averaged peak was measured. The results were compared with an age-matched control group.
DMD patients had reduced b-wave amplitudes both for the dark-adapted and for the bright-adapted standard flash ERGs (p<0.04). For the dark-adapted standard flash ERG they also had increased b-wave implicit times (p<0.01). For the ON protocol DMD patients had reduced amplitudes in both mesopic and photopic positive peaks (p<0.02). For the OFF protocol DMD patients had reduced amplitudes in the mesopic responses (p<0.02) but not in the photopic responses (p>0.05).
Since the Dp260 is located in the invaginated part of the synaptic terminal of the photoreceptors where both rods and cones connect to ON bipolar cells, its deletion might explain the reduced ERG amplitudes found in these patients. The reduction has been detected for both ON and OFF protocols in the mesopic condition, as the rod-to-ON bipolar cell signals are sent to both ON and OFF pathways via AII cells, and for the ON protocol in the photopic condition in which the ON pathway is affected exclusively.
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