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Athanasios Panorgias, Erich Sutter, John Werner; Topography and aging of the scotopic mfERG. Invest. Ophthalmol. Vis. Sci. 2013;54(15):6135.
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© ARVO (1962-2015); The Authors (2016-present)
To investigate the changes in the scotopic mfERG with retinal location and aging.
Fifty-eight normal subjects (age range: 18 - 88 years) were tested after 40 min of dark adaptation with a scotopic mfERG protocol. The responses were obtained with a DTL electrode and standard ground/reference gold cup electrodes, placed at the forehead and temporal canthus, respectively. The pupil was maximally dilated with 1% tropicamide and 2.5% phenylephrine. 61 unscaled hexagons were used. Three blank frames (one before the stimulus and two after) slowed the m-sequence. An m-sequence of 14 resulted in ~14 min recording time split into 30-sec segments. A linear polarizer and a Kodak Wratten-47B filter, placed in front of the stimulator (FMS III, EDI), produced scotopic luminances (bright and dark state luminances of -4.5 log cd s/m2 and close to zero, respectively). Only the blue LED of the system (~450 nm) was used. The responses were processed and grouped offline in nasal-temporal, superior-inferior, central disc (~20o diameter) and paracentral ring (inner radius ~10o, outer radius ~20o).
Paired t-tests showed statistically significant differences in both implicit time and amplitude of the b-wave between the central area and the paracentral ring (p=0.022 and p<0.001, respectively, a=0.05). The central area showed a delay compared to the paracentral ring while the paracentral ring showed higher b-wave amplitudes. Statistically significant differences were found in both latency and amplitude between nasal and temporal meridians (p<0.001, a=0.05 for both). The nasal meridian showed a delay in implicit time and the temporal meridian showed higher b-wave amplitude. No difference in amplitude was found between the superior and inferior meridians while a statistically significant difference found in implicit time with the inferior meridian showing a delay (p=0.033, a=0.05). The implicit time showed an aging effect of ~0.0015 log ms per year and the response density remained relatively stable up to the age of 60 years and then declined linearly by ~0.001 log nV/deg2 per year (based on regression analysis).
The increase in implicit time with age and the higher amplitude in the paracentral ring are consistent with the literature on rod aging and topography. The spatially-resolved responses provided by the mfERG is likely to be significant in diagnosis and treatment monitoring of diseases that produce outer retinal dysfunction.
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