Senescent Changes and Topography of the Dark-Adapted Multifocal Electroretinogram

Abstract

Purpose: To investigate the topographic changes of the dark-adapted multifocal electroretinogram (mfERG) across adulthood in the central retina and compare the topography between macular versus extramacular, nasal versus temporal, and inferior versus superior retinal areas.

Methods: Sixty-five subjects (18-88 years) received a comprehensive dilated eye examination to ensure the health of their retina and were tested with a dark-adapted mfERG protocol using a 61-hexagon pattern. The lens absorption of each subject was also estimated using a heterochromatic flicker photometry (HFP) paradigm.

Results: The response amplitude and latency of the dark-adapted mfERG showed a significant change with age, which was best described with a linear model. All the retinal areas examined demonstrated similar aging effects. The extramacular and temporal retina showed higher response amplitude and faster response latency when compared with the macular and nasal retinae, respectively. No difference was found in response amplitude and latency between the inferior and superior retina. The HFP results also showed a significant correlation with age, consistent with senescent increases in short wavelength absorption by the crystalline lens. However, the change in lens absorption did not exceed the magnitude of the change in response amplitude and latency.

Discussion: Our results indicate that there is a decline in dark-adapted retinal activity as measured with the mfERG. These aging processes affect rods and rod-bipolar cells. Their decrease in response can be attributed to both optical and neural factors.

Figure 1

The frame sequence used for recording the scotopic mfERGs. The m-sequence started with a blank frame, followed by the stimulus frame and two more blank frames. The stimulator's refresh rate was 75 Hz resulting in a frame duration of 13.3 msec for a total of 66.5-msec interstimulus interval. The figure illustrates 2 m-steps.

Figure 2

(a) The FMS III configuration with the Wratten 47B filter and the linear polarizer. The polarizer was mounted on a ring attached to the eyepiece of the FMS III. Marks on the FMS III and a linear scale attached to the rim of the polarizer ring allowed accurate rotation of the polarizer and the same polarization angle for each subject. (b) The luminance attenuation factor as a function of the polarizer's angle. We measured the luminance attenuation factor twice to ensure reproducibility of the desired experimental luminance. The solid curve is the best-fitted sinusoidal function.

Figure 3

The dark-adapted mfERG traces for two observers, a 20-year-old on the left and a 72-year-old on the right. Note the differences in amplitude and timing between the two subjects for the majority of the localized responses.

Figure 4

Amplitude and latency of the averaged approximately 40° dark-adapted mfERGs as a function of age. The left-most panel shows the grouping of the hexagons for the results reported in this figure. The middle panel shows the log nV/deg of the averaged responses as a function of age. The right panel shows the log latency of the dark-adapted mfERG responses as a function of age. The solid lines are linear regressions, and the dashed lines are 95% confidence bounds for the linear fit. For amplitude, the slope of the linear regression is −0.0032 nV/deg²/year (r = −0.4172, P < 0.01). For latency, the slope of the linear regression is 0.0013 log ms/year (r = 0.5744, P < 0.001).

Figure 5

Mean amplitude and latency for two retinal areas. The macular area of approximately 20° diameter and the extramacular area forming a ring of approximately 10° diameter between 10° and 20° retinal eccentricity (left panel). The middle and right panels show the log nV/deg and log ms of the averaged responses as a function of age. Red data points and fitted lines correspond to the macular area; blue data points and fitted lines correspond to the extramacular area. The dashed lines are the 95% confidence bounds for the linear regressions. For the macular area, the amplitude slope is −0.003 nV/deg²/year (r = −0.3278, P < 0.05) and the latency slope is 0.00123 log ms/year (r = 0.5255, P < 0.01). For the extramacular area, the amplitude slope is −0.00269 nV/deg²/year (r = −0.3230. P < 0.05) and the latency slope is 0.00128 log ms/year (r = 0.5579, P < 0.005).

Figure 6

Amplitude and latency of averaged responses for two retinal areas; the nasal retina (red) and the temporal retina (blue). See Figure 5 legend for details. Both areas subtend approximately 20°. The middle panel shows the log nV/deg as a function of age and the right panel the log latency as a function of age for both retinal areas. For the nasal retina, the amplitude slope is −0.00239 nV/deg²/year (r = −0.2958, P < 0.05) and the latency slope is 0.00127 log ms/year (r = 0.5171, P < 0.001). For the temporal retina, the amplitude slope is −0.0030 nV/deg²/year (r = −0.3399, P < 0.01) and the latency slope is 0.00122 log ms/year (r = 0.5595, P < 0.001).

Figure 7

Amplitude and latency of averaged responses for the superior retina (red) and inferior retina (blue). See Figure 5 legend for details. Both areas subtend approximately 20°. The middle panel shows the log nV/deg as a function of age and the right panel the log latency as a function of age for both retinal areas. For the superior retina, the amplitude slope is −0.00203 nV/deg²/year (r = −0.2545, P < 0.05) and the latency slope is 0.00162 log ms/year (r = 0.6279, P < 0.001). For the inferior retina, the amplitude slope is −0.00237 nV/deg²/year (r = −0.2987, P < 0.05) and the latency slope is 0.00114 log ms/year (r = 0.4863, P < 0.001).

Figure 8

The results of the HFP experiment as a function of age. The line is the best-fitted linear regression. The slope of the regression line is −0.0020 (r = −0.591, P < 0.001).