At the initial evaluation of our volunteers, there were no significant differences among groups regarding age (Kruskal-Wallis test = 0.63; p = 0.73) or gender (Kruskal-Wallis test = 0.44, p = 0.80).
3.1 Group A – Asymmetrics
3.1.1 – Visual Acuity
Group A (presenting a difference of one line of acuity between both eyes) was formed by 6 subjects (5 females and 1 male) with ages between 20–24 years (with a mean age of 22.5\((\pm 1.5))\). Three of them showed a dominance of their right eye (DO3, DO4, DO6), and the remainder had dominance of their left eye (DO1, DO2, DO5). Five of them (DO2, DO3, DO4, DO5, DO6) were also submitted to placebo stimulation after the washout period (placebo group A).
For 5 of the 6 volunteers actively stimulated, improvement was seen in visual acuity after the continuous Theta Burst Stimulation session (Fig. 1). Volunteer number DO3 showed no changes in visual acuity with continuous Theta Burst Stimulation. The data presented in graph 1 concerns volunteers’ non-dominant eyes subjected to cTBS. The placebo group showed no relevant changes after the placebo stimulation. This data is presented in table 2.
Mean visual acuity value for the non-dominant eye for this group, before continuous Theta Burst Stimulation, was − 0.02 logMAR\((\pm 0\).07), and of -0.1 logMAR \((\pm 0.09)\) after continuous Theta Burst Stimulation. Thus, we found significant differences between before and after stimulation (Wilcoxon = -2.02; p = 0.04) in group A actively stimulated volunteers.
Regarding placebo group A, there were no significant changes in visual acuity between before and after (Wilcoxon = -1.41; p = 0.16). Visual acuity results for placebo group A are presented in table 2 in order to a better understanding of data, due to the non-significant changes observed.
3.1.2 – Suppressive Imbalance
For Suppressive Imbalance, all volunteers from group A actively stimulated showed improvement after only one session of continuous Theta Burst Stimulation, which shown in Fig. 2, with the suppressive imbalance values closer to 0. The mean suppressive imbalance value before and after continuous Theta Burst Stimulation was 0.05 \((\pm 0.08)\) and 0.02 (\(\pm 0.04)\), respectively. We found significant differences between before and after continuous Theta Burst Stimulation suppressive imbalance responses (Wilcoxon = -2.21; p = 0.03).
Concerning the placebo group A, there were no changes for suppressive imbalance for either the five volunteers after placebo stimulation (Wilcoxon < 0.0001, p > 0.99). Data are shown in table 3.
3.2 Group B – Amblyopes
3.2.1 – Visual Acuity
In this group, there were 19 volunteers (15 females and 4 male) with ages among 19–51 years, and a mean age of 28.0 \(\left(\pm 10.3\right) \text{y}\text{e}\text{a}\text{r}\text{s}.\) Nine of them showed right eye dominance, and the other ten showed left-eye dominance. They were split into two sub – groups: eight were submitted to a placebo stimulation (placebo group B) and eleven were submitted to an active stimulation.
There were clear visual acuity differences before and after continuous Theta Burst Stimulation in actively stimulated patients of group B (Fig. 3). Volunteer A9 showed no improvement, and volunteer A8 showed only slight improvement (these volunteers had in common the fact that they had never had amblyopia treatments before, and both were women). Mean visual acuity value before continuous Theta Burst Stimulation for the actively stimulated group was 0.34 logMAR (\(\pm 0.21)\), and 0.22 logMAR \((\pm 0.17)\) after continuous Theta Burst Stimulation. Data presented in Fig. 3 shows volunteers’ amblyopic eyes actively stimulated values.
Placebo group B showed no changes in visual acuity. Data is presented in table 4. Significant differences were seen in visual acuity between before and after continuous Theta Burst Stimulation (Wilcoxon = -2.82; p = 0.01), for the actively stimulated group. Contrariwise, no significant differences were found for visual acuity of the placebo group B, after placebo stimulation (Wilcoxon < 0.0001, p > 0.99).
Significant differences were found for visual acuity between the placebo group B when compared with the group B that was actively stimulated (Mann – Whitney = 4.50, p > 0.00).
3.2.2 – Suppressive Imbalance
For suppressive imbalance nine of the 11 volunteers in group B that were actively stimulated showed improvement in their suppressive imbalance, suggesting that, after continuous Theta Burst Stimulation, their eyes became more balanced. This can be observed in Fig. 4, with suppressive imbalance values coming closer to zero. Volunteers A13 and A14 did not show any apparent improvements in their suppressive imbalance; these volunteers had in common the fact that they showed the same level of asymmetry (exactly two lines of visual acuity difference between their eyes), the same amblyogenic factor (strabismus), and both had had occlusion as a child. Mean value of suppressive imbalance for the actively stimulated group before continuous Theta Burst Stimulation was 0.25 (\(\pm 0.17)\), which shifted to 0.12 \(\left(\pm 0.12\right)\) after continuous Theta Burst Stimulation, showing a significant difference between before and after continuous Theta Burst Stimulation (Wilcoxon = -2.67; p = 0.01).
For suppressive imbalance for placebo group B, no relevant changes were seen after placebo stimulation. Data is presented in Table 5 (Wilcoxon = -1.00; p = 0.32).
We found significant differences for suppressive imbalance between the placebo group B when compared with the group B that was actively stimulated (Mann – Whitney = 13.50, p = 0.01).
3.3 Group C – Normal binocular vision (NBV)
3.3.1 – Visual Acuity
Group C had 10 volunteers with normal binocular vision, which were split into 2 sub-groups: 5 were subjected to placebo stimulation (placebo group C) and 5 were subjected to active stimulation. All 10 subjects had symmetry between their eyes both in visual acuity and suppressive imbalance (Tables 2 and 3).
There were no changes in the visual acuity of either eye in the 5 volunteers with normal binocular vision that were subjected to a single session of continuous Theta Burst Stimulation. The visual acuity of placebo group C remained at its baseline values. As shown in Tables 2 and 3, the mean values for visual acuity before and after stimulation remained the same in both eyes, both for the group that was actively stimulated and for placebo group C, neither of which showed any relevant differences after Transcranial magnetic stimulation was applied.
We did not observe before-vs-after visual acuity differences in either the right (Wilcoxon = -1.00, p = 0.32) or left eyes (Wilcoxon = -1.00, p = 0.32) in the 5 volunteers who underwent placebo stimulation (placebo group C).
Concerning the 5 volunteers that were actively stimulated, right and left eye values before and after continuous Theta Burst Stimulation were not significantly different (Wilcoxon < 0.0001; p > 0.99).
No significant differences were found when the right and left eye values of the placebo group C were compared with right and left eye values of the group that was actively stimulated before and after stimulation (Wilcoxon = -0.153, p = 0.88 and Wilcoxon = -0.05, p = 0.96).
We found no significant differences for visual acuity between placebo group C when compared with the group C that was actively stimulated (Mann – Whitney = 10.00, p = 0.32).
Regarding suppressive imbalance, no changes were seen in the balance between eyes after a single session of continuous Theta Burst Stimulation in both the 5 stimulated and in the 5 placebo group C volunteers; subjects eyes remained completely balanced, just as they were before the stimulation (Wilcoxon < 0.0001, p > 0.99).
We did not find any significant differences for suppressive imbalance between the placebo group C when compared with the group C that was actively stimulated (Mann – Whitney = 12.50, p = 1.00).
3.4 – Comparison between the three groups (A,B,C)
3.4.1- Visual Acuity
Fifteen out of the 27 volunteers (55.6%) showed improvement in their visual acuity after one session of continuous Theta Burst Stimulation. Volunteers A3 and A9 showed no improvement in the control parameters, having maintained their visual acuity at the same level as before the session (Fig. 3). The 10 volunteers with normal binocular vision kept their baseline values of visual acuity after continuous Theta Burst Stimulation session. The mean value of visual acuity before the continuous Theta Burst Stimulation session was 0.07 logMAR \((\pm\) 0.28), shifting to 0.01 logMAR (\(\pm 0.22)\) after continuous Theta Burst Stimulation. Given that the visual acuity values of the 10 volunteers with normal binocular vision (group C) were the same between their eyes, we used right eye values, to maintain homogeneity between subjects. Their respective values of visual acuity, before and after continuous Theta Burst Stimulation, are presented in Tables 6 and 7.
As we showed that there were no significant differences in the group of normal binocular vision (C), between the stimulated and the placebo group (Mann-Whitney = 8.50, p = 0.40), they were treated as only one group.
A Kruskal Wallis comparison between the three groups found significant differences between the group of amblyopes and the group of normal binocular vision (Kruskal-Wallis test = 13.03, p < 0.0001). In contrast, there were no significant differences between the asymmetric group and the group of amblyopes (Kruskal-Wallis = 3.85, p = 0.96) or between the asymmetric group and the normal binocular vision group (Kruskal-Wallis = -9.18, p = 0.06).
Regarding the comparisons between the three placebo groups (A,B,C) for visual acuity, no significant differences between all three groups were found (Kruskall – Wallis = 2.42, p = 0.30).
3.4.2- Suppressive imbalance
Fourteen subjects showed improvement in their suppressive imbalance after continuous Theta Burst Stimulation, with a reduction in this control parameter; their respective suppressive imbalance values were brought closer to zero, indicating an improvement in the balance between their eyes. Volunteers A13 and A14 did not show any improvement in this control parameter (Fig. 4). The 10 volunteers with normal binocular vision remained with their eyes balanced, just as they were before the continuous Theta Burst Stimulation session. Mean suppressive imbalance values were compared: mean before continuous Theta Burst Stimulation was of 0.17 \((\pm 0.16)\), shifting to 0.05 \((\pm 0.09)\) after continuous Theta Burst Stimulation.
There were no significant differences between the volunteers with normal binocular vision, who were actively stimulated, and those with a normal binocular vision which were in the placebo sub-group (Mann-Whitney = 1.93, p > 0.99); therefore, they were all considered in the same group (C). Kruskal-Wallis Test was used to make comparisons between the three groups. No significant differences were found between the asymmetric group and amblyopic group (Kruskal-Wallis = 1.92, p > .99). On the other hand, we found a significant difference between the asymmetric versus the group of normal binocular vision (Kruskal-Wallis = -10.67, p = .02) and between the amblyopic versus the group of normal binocular vision (Kruskal-Wallis = 12.59, p < .0001).
Regarding comparisons between the three placebo groups (A,B,C) for suppressive imbalance, there were no significant differences found between all three groups (Kruskall – Wallis = 1.25, p = 0.54).
The dominant eye in the asymmetric group was tested and evaluated before and after continuous Theta Burst Stimulation, as well as the dominant eye in the amblyopic group. No significant changes were found.