Abstract
Purpose:
To investigate the changes in the scotopic mfERG with retinal location and aging.
Methods:
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).
Results:
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).
Conclusions:
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.
Keywords: 413 aging •
510 electroretinography: non-clinical