https://www.tomshardware.com/news/htc-vive-pro-eye-tracking-tobii-hands-on,38383.html
 
The Vive Pro Eye is, as the name would suggest, a new SKU with integrated eye tracking in the Vive Pro HMD. Working together with Tobii, the Vive Pro Eye allows for a more natural control mechanism within VR via eye controls. Developed by 2 Bears Studio, HTC Vive's internal development team, VIVE Sync is an enterprise-level collaboration tool that was piloted very recently and is made all the better with the Vive Pro Eye. Prepar3D has been around for a while, finding use as a powerful simulation and training software for aircrafts in general. The Vive team told me that it took all of two weeks to get eye tracking added to make use of the Vive Pro Eye, and the experience here is effectively similar as with Ovation in that it tracks where the trainee's eyes are focused on. So VR continues to improve but until more people use it sales will be low in my personal opinion.