PSP patients show extremely slow vertical saccades and frequent square wave jerks. Horizontal saccades will end up being affected as well over the course of the disease. Eye movements, particular along the vertical plane will become restricted in the later stages of the disease. Pursuit is also decomposed. But the problem with decomposed pursuit is that any neurodegenerative disorder can provide a delay in pursuits so this finding is not very specific. So, PSP gives you slow vertical saccades and frequent square wave jerks at the initial stages.