Visual symptoms in postural tachycardia syndrome: An investigation of position‐dependent visual exploration

Figures

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  FIGURE 1. Study protocol. Participants completed three visual exploration tasks (eye tracking) in total, once in the supine position and twice during 60° HUT. The PLR was taken five times, each before and after a visual exploration task. Once in the supine position and once at the end of the HUT phase, all participants rated their symptoms of orthostatic intolerance. HUT, head‐up tilt; PLR, pupillary light reflex.

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  FIGURE 2. Results of eye tracking during visual exploration: fixation metrics. (a) Bar graphs showing the number of fixations of patients with POTS (dark grey bars) and control subjects (light grey bars) in the supine and 60° HUT positions (first and second HUT phase). (b) The same is shown for cumulative fixation duration. For number of fixations, there were main effects of position (F(1, 28) = 6.08, p = 0.007) and group (F(1, 28) = 8.32, p = 0.007) as well as a significant interaction of position × group (F(1, 28) = 4.29, p = 0.024). For cumulative fixation duration, the analysis showed a main effect of position (F(1, 28) = 3.83, p = 0.034) and an interaction of position × group (F(1, 28) = 5.20, p = 0.012). Values are given as mean ± SEM. HC, healthy controls; HUT, head‐up tilt; POTS, postural tachycardia syndrome. **p ≤ 0.01, ***p ≤ 0.001.

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  FIGURE 3. Results of eye tracking during visual exploration: saccade metrics. (a) Bar graphs showing the number of saccades of patients with POTS (dark grey bars) and control subjects (light grey bars) in the supine and 60° HUT positions (first and second HUT phase). (b) The same is shown for maximum saccade peak velocity and (c) cumulative saccade amplitude. The analysis of number of saccades showed significant main effects for position (F(1, 28) = 4.87, p = 0.016) and group (F(1, 28) = 10.71, p = 0.003) as well as an interaction of position × group (F(1, 28) = 4.48, p = 0.021). For maximum peak velocity of saccades, there was a main effect for group (F(1, 28) = 7.34, p = 0.011) and a significant interaction of position × group (F(1, 28) = 3.84, p = 0.034). For cumulative amplitude of saccades, the analysis showed a significant main effect for group (F(1, 28) = 14.43, p < 0.001) and an interaction of position × group (F(1, 28) = 3.69, p = 0.038). Values are given as mean ± SEM. HC, healthy controls; HUT, head‐up tilt; POTS, postural tachycardia syndrome. *p ≤ 0.05, **p ≤ 0.01, ***p ≤ 0.001.

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  FIGURE 4. Saccade main sequence. (a) Graphs showing the relationship between peak velocity and amplitude of saccades (saccade main sequence) of patients with POTS (red) and control subjects (blue) in the supine position. (b) The same is shown for the 60° HUT position (first HUT phase) and in (c) for the 60° HUT position (second HUT phase). HC, healthy controls; HUT, head‐up tilt; POTS, postural tachycardia syndrome.

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  FIGURE 5. Heat maps: illustration of one image. Exemplary visualization of gaze behaviour of patients with POTS and control subjects in the supine position and during 60° HUT (second HUT phase). Each image contains the cumulative fixations of five participants who were shown the image in the same position. The warmth of the colour and size of the spots represent the number and duration of fixation; that is, the warmer the colour, the more and longer participants fixated the spot. HUT, head‐up tilt; POTS, postural tachycardia syndrome.

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  FIGURE 6. Results of eye tracking during visual exploration: areas of interest. (a) Bar graphs showing the number of fixations to the centre and periphery of the field of view, respectively, of patients with POTS (dark grey bars) and control subjects (light grey bars) in the supine and 60° HUT positions (first and second HUT phase). (b) The same is shown for cumulative fixation duration. The analysis of number of fixations in each area of interest (centre vs. periphery) showed main effects of position (F(1, 28) = 5.10, p = 0.013) and group (F(1, 28) = 7.57, p = 0.010) as well as a significant interaction of position × group (F(1, 28) = 3.88, p = 0.033). For cumulative fixation duration, there was a significant main effect for position (F(1, 28) = 4.11, p = 0.028) and an interaction of position × group (F(1, 28) = 4.41, p = 0.022). Values are given as mean ± SEM. HC, healthy controls; HUT, head‐up tilt; POTS, postural tachycardia syndrome. *p ≤ 0.05, **p ≤ 0.01.