Fig. 2

The visually guided saccades from healthy subject and PSP patient are compared. Panel a illustrates normal visually guided vertical saccade from a healthy subject. Panels d,g depict two examples of visually guided vertical saccades from the same PSP subject. Panel j depicts eye positions during horizontal saccade. In panels (a,d,g,j) the eye position is plotted on the y-axis while x-axis depicts corresponding time in seconds. Black line represents the vertical eye position, while green traces depict horizontal eye position. Grey dashed line is the baseline, i.e. the straight-ahead position, while blue dashed line depicts the desired position. The arrows depict interruption in the saccades, in one type of interruption (blue arrow) the eyes continue to move at slower velocity during interruption, while in other type (green arrow) the slower eye movement in the opposite direction. The third type of interruption (red arrow) is where the eye movements completely stop during the interruption. Panels b,e, h,k depict eye velocity. Panel B depicts eye velocity of normal visually guided saccade recorded from the healthy subject, while panels (e,h) depict vertical eye velocity during vertical saccade in PSP. Green line in panel K illustrates normal horizontal eye velocity during horizontal saccade in PSP. In these subplots the eye velocity is plotted on y-axis while x-axis illustrates corresponding time. Red arrow illustrates interruption in saccade when eye velocity was zero, green arrow is when eye moved at slower velocity in the opposite direction, blue arrow is when eyes moved in the same direction at slower velocity. Panels c,f,i,l depict trajectories of horizontal and vertical saccades. Panel C shows the normal saccade from the healthy subject, while panel (f,i) are vertical saccades in PSP, and panel l is the horizontal saccade in PSP. In these plots the green dot depicts the start point, while the red dot is the stop point; grey dashed line is the desired path of the eye movement. Vertical saccades have curved and serpentine path depicting the irregularity in the trajectory. Such curvature is also present in the horizontal saccade but to much lesser extent (adapted from Shaikh et al. [121])