highly significantP < 0.001
The mean (± SEM) cAL increase was 11 ± 2 μm at 3 D, 14 ± 2 μm at 6 D, and 26 ± 2 μm at 9 D, with all pairwise comparisons highly significant (all P < 0.001), except the difference between the 3 and 6 D stimuli ( P = 0.48).