Multifocal ERG responses in infants

Abstract

Purpose: To assess function of the central retina in 10-week-old infants, multifocal electroretinograms (mfERGs) were recorded. mfERG responses represent postreceptor retinal activity.

Methods: In infants (n = 23) and adults (n = 10), mfERG responses to both unscaled and scaled 61 hexagon arrays were recorded. Amplitude and implicit time of negative (N(1), N(2)) and positive (P(1)) peaks of the first-order kernel were examined. The response from the entire area stimulated and responses to concentric rings were analyzed separately. The overall averaged response of the first slice of the second-order kernel was also evaluated. Results from infants and adults were compared.

Results: Amplitudes of the infants' responses (N(1), P(1), N(2)) were significantly smaller and implicit times were significantly longer than those of adults. In infants, amplitude and implicit time varied little with eccentricity. In adults, amplitude decreased with eccentricity, whereas implicit time varied little. In infants, the second-order kernel was relatively more attenuated than the first-order kernel.

Conclusions: The infants' mfERG responses indicated immaturities of processing in the central retina. Infant-adult differences in the distribution of cones and bipolar cells may account for the results.

Figure 1

Sample mfERG records of Infant 15. The 61 first order responses to unscaled (upper trace array) and scaled (lower trace array) stimuli are shown. This infant had amplitudes that were near the median in both conditions. In each panel, a schematic drawing of the stimulus is shown.

Figure 2

First order kernel responses averaged across all 61 hexagons in the unscaled (upper panel) and scaled (lower panel) conditions. Responses are shown for infants who had P₁ amplitude near the minimum (Infant 19), median (Infant 15), and maximum (Infant 14) values in both stimulus conditions. Responses from an adult (Adult 10) with P₁ amplitude near the median are also shown (lowest trace in each panel). For each subject, waveforms in the unscaled and scaled conditions are similar. In each panel, the calibration bar pertains to all subjects.

Figure 3

Amplitude (upper panels) and implicit time (lower panels) of overall averaged responses for unscaled (left) and scaled (right) stimuli in infants (filled bars) and adults (open bars). Means (± SEM) for N₁, P₁, and N₂ of the first order kernel are shown.

Figure 4

Ring averages to unscaled (upper panels) and scaled (lower panels) stimuli. The response to the central hexagon (ring 1) and the average response to all hexagons in each concentric ring (2 through 5) are shown. Responses from infants with P₁ amplitude at the minimum (Infant 19), median (Infant 15), and maximum (Infant 14) are shown. For comparison, ring averages for an adult (Adult 10) are also plotted. The calibration bar (lower right panel) pertains to all panels.

Figure 5

Mean amplitude (± SEM) for infants (filled circles) and adults (open circles) for N₁, P₁, and N₂ of the first order kernel plotted for rings 1 through 5. Responses to unscaled stimuli are shown on the left and to scaled stimuli on the right.

Figure 6

Mean implicit time (± SEM) for infants (filled circles) and adults (open circles) for N₁, P_1, and N₂ of the first order kernel plotted for rings 1 through 5. Responses to unscaled stimuli are shown on the left and to scaled stimuli on the right.

Figure 7

The second order response averaged across all 61 hexagons in the unscaled (upper panel) and scaled (lower panel) conditions. The peak and trough used to specify amplitude are indicated. Responses are shown for the same subjects as in Figures 2 and 4. In each panel, the calibration bar pertains to all subjects.

Figure 8

The amplitude of the second order kernel plotted (upper panels) for unscaled (left) and scaled (right) stimuli for infants (filled bars) and adults (open bars). The ratio of the amplitude of the second to first order response (lower panels) is plotted for infants and adults. Means (±SEM) are shown.