In all, we analyzed approximately 6000 fixational saccades from NM, approximately 47,000 fixational saccades from SM1 to 5, and approximately 11,000 fixational saccades from PM.
Figure 2 shows the distribution of fixational saccade radial amplitudes in the normal and one of the strabismic monkeys (SM2). Overall, the pattern of amplitude distribution was similar in normal and strabismic monkeys. The median amplitude of fixational saccades in the normal monkey was 0.33° and is similar to that previously published.
15 The median amplitude of fixational saccades in the strabismic monkey was 0.74° (dotted line), which is significantly greater than that of the normal monkey.
Figures 3A,
3B show a box-plot summary of fixational saccade amplitude across all targets and monocular/binocular viewing conditions in the viewing and nonviewing eye of each animal. Note that for this and other plots there were no data included for the nonviewing eye during binocular viewing in normally aligned animals NM and PM. In all strabismic animals, the viewing eye during binocular viewing is the eye that is fixating the target and the nonviewing eye is the deviated eye. Median amplitudes of fixational saccades from the viewing eye of three strabismic monkeys were larger than that of the normal monkey (Kruskal-Wallis ANOVA on ranks H[6] = 9624.03,
P < 0.001; Dunn's method for post hoc testing
P < 0.05). Fixational saccades in the nonviewing eye of all the strabismic monkeys were larger than that of the normal monkey (Kruskal-Wallis ANOVA on ranks H[5] = 4510.70,
P < 0.001; Dunn's method for post hoc testing
P < 0.05). Although PM did not show eye misalignment, fixational saccade amplitude in this animal was also significantly greater than that of NM.
We also calculated the frequency of fixational saccades in the viewing and nonviewing eyes of the animals, and these data are summarized in
Figure 4. Frequency of fixational saccades was increased in three of five strabismic monkeys in comparison with the normal monkey in the viewing eye (Kruskal-Wallis ANOVA on ranks H[6] = 196.69,
P < 0.001; Dunn's test
P < 0.05) and one monkey in the nonviewing eye (Kruskal-Wallis ANOVA on ranks H[5] = 201.82,
P < 0.001; Dunn's test
P < 0.05). Fixational saccade frequency in PM was significantly higher than NM and in many cases even higher than in the strabismic monkeys.