In addition to the expected photoreceptoral effects, we also find changes to the rod PII response which is thought to be a measure of ON-bipolar cell activity.
46 The ω-3
− group exhibits a delay in timing of the PII response (
P < 0.001) consistent with the literature.
7 8 17 18 A two-sided
t-test did not show a significant reduction in the PII amplitude (
P = 0.05) consistent with studies in monkeys
7 11 17 and rats.
8 47 However, a significant decrease in PII amplitude was reported in ω-3
− guinea pigs.
14 As the probability (
P = 0.05), using our conservative approach of a two-tailed
t-test is very close to our criterion of α = 0.035, we cannot be confident that this finding is real. Indeed, the power of this experiment is 0.56, which is less than desirable (power = 0.8). Given the a priori expectation from the literature that ω-3 deficiency should either decrease or leave the PII amplitude unaltered, a one-sided
t-test can be adopted to increase power. Note that a similar approach does not salvage the Rm
PIII. This analysis returns
P = 0.027; thus, it is likely that the PII amplitude decrease found with ω-3 deficiency is also real. Therefore, for both the PIII and PII finding the ω-3
−-induced loss is frustrated by the small magnitude of change coupled with the modest experimental variability limiting experimental power. It is also worth noting that when normalized
(Fig. 8A) , the PII loss was significantly removed from control variability (96.5% CI), supporting our contention.
The cone PII was not significantly affected with ω-3 deficiency. This finding is in contrast to the loss in amplitude found using a 30-Hz flicker stimulus to elicit cone responses in guinea pigs.
14 This difference may arise as the flicker stimulus used in past work elicits a complex interaction between the ON- and OFF-bipolar cells,
48 whereas our paired-flash methodology favors ON-bipolar cell isolation.
27 Nevertheless, it is of interest that the cone PII trend with ω-3 deficiency followed a tendency similar to that of the rod PII. More specifically, the trend for a decrease (−8.0% ± 2.9%) in cone PII amplitude was consistent with that of the rod PII loss (
P = 0.92). However, the trend in cone PII delay (4.3% ± 1.9%) was less than that of the rod PII (13.6% ± 2.3%
P < 0.001). Indeed, a preferential effect of ω-3 on rods over cones is consistent with studies in infants.
15 16 The cause of this preference is unknown and requires further investigation.