Eye movements can be either pursuit ( smooth) or saccades(fast). Both are important , but accurate fast eye movements are particularly important in reading. Being able to accurately scan across a page is a learned skill. Different languages are written differently so Japanese readers have good vertical , right to left eye movements whereas English requires good left to right smaller jump movements and one large right to left movement to start each new line.
Many children start to read at an age before they have well established jump eye movements and if these don’t develop quickly, this can be an obstacle to learning to read with frequent skipping of words or lines, or even reading some words backwards as the eyes back track from an overshoot.