The eye muscles have to be fast. Just to track an object involves at least seven different highly coordinated movements. If eye muscles were slow, we couldn't focus on anything moving around us.

Diplopia is also known as double vision. It occurs when the pair of muscles that control a particular eye movement weaken and become uncoordinated. When the images are not properly aligned ...

Horizontal saccadic eye movements rather than gaze fixation correlated ... from images projected on the retina and inputs from the muscles that move the eyes, which help reduce body sway.

The frequency and duration of large muscle group leg movements during sleep change over time, and show distinct sleep stage differences.

These include stiffness of neck and trunk muscles (rigidity), slowness of movement (bradykinesia), and impaired balance. Unlike classic Parkinson's disease, tremor is rarely a prominent part of PSP.