|
RESULTS
Comparison of peak latencies of congenitally blind and normal sighted subjects showed significant differences between (i) Pa wave (the maximum positive peak between Na and 35ms) and (ii) Nb wave (the maximum negative peak between 38 and 52ms) peak latencies. The latencies of both components were shorter in the congenitally blind compared to subjects with normal vision. However, with the Tukey test for multiple comparisons between mean values the peak latencies of Pa and Nb waves were not significantly different between congenitally blind and normal sighted subjects [p >.10, for both comparisons]. With the ANOVA, for Pa wave peak latency [F for Factor A (two groups) = 5.64, since F0.05 (2) 1, 36 = 5.47, hence p < 0.05] and for Nb wave, [F for Factor A (two groups) = 4.70, since F.0.05 (1) 1, 36 = 4.1 1, hence p < 0.05]. The peak latencies of wave V and Na wave did not show a significant difference between groups or repeat recordings and also interaction between factors, i.e., A x B (p > 0.50). The F value for df = 1.36 has been derived by linear interpolation from the df = 1,30 and df = 1,40 from the standard table as described (Zar, 1984).
Out of the 10 pairs of subjects studied: (1) in 5 blind subjects both Pa and Nb waves had shorter latencies than those of the matched, sighted subjects, (2) in another 3 blind subjects the Pa wave had a longer latency while Nb wave was shorter than the matched normal sighted, there were also (3) 2 blind subjects who had a shorter Pa wave latency and longer Nb wave latency when compared to the corresponding normal sighted subjects. Examples of 1, 2 and 3 are shown in Figure 1.
There were no significant differences between the peak amplitudes of the AEP-MLR components of congenitally blind and normal sighted groups recorded at Cz (Two factor ANOVA,  FIGURE 1: Three examples of AEP-MLRs recorded in congenitally blind (CB) and subjects with normal vision (NV), with two recordings each. The first example (1) shows shorter latencies of Pa and Nb is CB compared to NV for both recordings. In the second example (2), Pa latency is shorter (first recording) or the same (second recording) in CB compared to NV, while Nb latency is longer. The third example shows longer Pa latency and shorter Nb latency in CB compared to NV, for both recordings.
Factor A = groups, p > 0.50 for all comparisons, Factor B = repeat recordings, p > 0.50, and interaction between factors (A x B), p > 0.50.
The peak amplitudes of congenitally blind and normal sighted subjects showed significant differences in the Pa and Nb wave amplitudes recorded at Cz and Oz. For Pa [F for Factor B = sites of recording (Cz, Oz) = 27.2, since FO.00 1 (2) 1, 76 = 13.24, hence p < 0.00 1 ], and for Nb wave peak amplitude [F for Factor B = 10.6 since FO.002 (2) 1, 76 = 9.8, hence p < 0.002]. The Tukey test for multiple comparisons between the peak amplitudes showed a significant difference between the mean value at Cz and at Oz, but not between the groups. The Pa peak amplitude recorded at Cz was significantly higher than that recorded at Oz for both congenitally blind [q = 4.40, since q at probability level 0.025, for df = 76, 4 = 4.14, hence p < 0.025] and normal sighted subjects [q = 6.04, since q at probability level 0.001, for df = 76, 4 = 5.60, hence p < 0.001]. With the Tukey multiple comparison test the amplitudes of the Nb wave recorded at Oz and Cz were not significantly different for both congenitally blind and normal sighted subjects (p > 0.50).
The group average values of peak amplitudes and latencies of the four components studied, for the congenitally blind and normal sighted subjects are given in Table 1.
|
