Table 1.
Clinical characteristics of individual patients.
Figure 1.
Scanning Laser Opthalmoscope photo’s.
SLO photographs of all JMD participants. Participant 6 (lower right) was excluded due to the evident overlap of fixation and fovea. Interpolated visual field task images are shown below each respective SLO image. These show the visual field defect (VFT) for an 18° by 18° degrees visual field. Dark areas represent the point in the visual field where there was a defect, white represent no defect (ranging from 0–100%). Because the VFT measurements are based on binocular viewing and the SLO images are from each eye separately they not always clearly translate to one another [21], [26].
Figure 2.
Panel A shows a schematic overview of the fixation-offset paradigm as used by Machado & Rafal [32]. After drift correction participants are instructed to keep a steady fixation within the four anchors. As soon as a target appears they are instructed to make an eye-movement to that target as fast as possible. Presently, we focussed on the fixation phase (before target presentation) of this paradigm. Panel B shows the adaptation used in the PRL simulation version of this paradigm. Prior to the normal trial procedure (but after drift correction), participants had to align a gaze-controlled alternate eccentric fixation point over a central fixation cross. This led them to use their peripheral vision to fixate on the central fixation cross before the start of the trial. In panel B the “eyeball” symbol represent the true fixation, the ‘+’ sign represents the central fixation and the circled ‘+’ sign represents the eccentric fixation point that was controlled by the participants eye movement. There was no minimum fixation time during alignment of the eccentric fixation point that participants had to maintain for the trial to start. However, should participants make a saccade directing the eccentric fixation to the central fixation cross and then press the spacebar, the subsequent saccade parser would have detected a saccade at trial start and the trial would have been removed from subsequent analysis.
Figure 3.
Time-course and scatterplot examples for different types of trials.
Panels A, C and E show example time-courses of eye-position over time, lines indicate horizontal (red) and vertical (blue) displacement over time. The example time-courses illustrate measurement with (A) and without (C) an intrusive saccade in control subjects and a typical trial without saccades or blinks of a JMD patient (E). Panels B, D and F show the corresponding eye-positions across the entire measurement duration, indicating the effect of saccade and blinks on the displacement spread (Panel B). Displacement was summarized by the BCEA and examples are shown in blue circles in panels D and E. Only trials that did not include these intrusive saccades or blinks were included in the analysis of the BCEA, displacement and power spectral densities.
Figure 4.
Number of intrusive saccades during fixation.
The average number of intrusive saccades per trial are shown. Significant differences are marked: p<0.001 = ***, p<0.01 = ** & p<0.05 = *. This figure shows that the JMD group (1 degree [M: 0.47 SD: 0.23], 3 degrees [M: 0.68 SD: 0.20]) made significantly more intrusive saccades compared to healthy controls (1 degree [M: 0.06 SD: 0.04], 3 degrees [M: 0.11 SD: 0.07]) and controls performing the simulation (1 degree [M: 0.07 SD: 0.06], 3 degrees [M: 0.09 SD: 0.06]). It also shows that in the control group people made less intrusive saccade in the 1-degree condition.
Figure 5.
The start-to-end displacement in degrees of visual angle is shown. Significant differences are marked: p<0.001 = ***, p<0.01 = ** & p<0.05 = *. This figure shows that patients with JMD (1 degree [M: 0.78 SD: 0.22], 3 degrees [M: 0.69 SD: 0.14]) deviated more from their original fixation at the end of the fixation phase compared to controls in both the normal (1 degree [M: 0.40 SD: 0.08], 3 degrees [M: 0.41 SD: 0.14]) and simulation (1 degree [M: 0.34 SD: 0.12], 3 degrees [M: 0.34 SD: 0.12]) paradigm.
Figure 6.
Fixation stability during fixation.
The fixation stability in squared degrees as measured with a bivariate contour ellipse area (see figures 3B and 3D for an example). Significant differences are marked: p<0.001 = ***, p<0.01 = ** & p<0.05 = *. The “§” marks a trend. This figure shows that fixation was more unstable in the JMD group (1 degree [M: 0.33 SD: 0.20], 3 degrees [M: 0.44 SD: 0.49]) compared to the healthy control group (1 degree [M: 0.08 SD: 0.02], 3 degrees [M: 0.09 SD: 0.04]). The difference between the JMD group and the simulation group (1 degree [M: 0.07 SD: 0.03], 3 degrees [M: 0.07 SD: 0.02]) was not significant but a Bonferroni corrected p-value of 0.067 might be considered a trend.
Figure 7.
Power spectral densities for the one and three degrees condition. The grey bars represent the 95% confidence interval (CI) of the control group mean. Each blue line represents one JMD patient. This figure shows that JMD patients had significant more power in the lower frequencies, indicating that low frequency eye-movements dominate the differences in displacement and fixation stability.