That's a well known video driver bug in MacOS 10.10. Apple is aware of these bugs in the OS and is working on a solution.
Until Apple releases a fix, you can disable GPU drawing in Photoshop's preferences and relaunch Photoshop to avoid the OS driver bugs.
If you really need the GPU features in Photoshop, then you may need to consider downgrading to a more stable version of MacOS.
Looks as the problem is solved so far... Thank you very much!