I love hearing about research like this done on musicians (and other artists). I wouldn’t be surprised if something similar hasn’t been done for athletics, so it’s nice to see that musicians are taking advantage of the technology too.
In this video they show the difference between an older, more experienced, pianist and a younger, less accomplished, pianist. They tracked both of their eye movements while playing a memorized piece and also sight reading. While playing the memorized pieces the experienced pianist visual range on the keyboard was much more stable and consistent than the inexperienced pianist.
The results of the experienced pianist sight reading is directly relevant to anyone sight reading. His eyes are scanning ahead of where he is playing. It also jumps between the treble clef and bass clef staves consistently. This skill of reading ahead is perhaps one of the most important things to develop for sight reading.