By TOM BOWSER
Enable "Commands keyboard Focus" by clicking on the Commands Keyboard Focus button (a/z) at the upper right corner of the Pro Tools Edit window. See the image below.

Press and hold down the Ctrl + Alt keys:
- press the [ (left bracket) key to Zoom out vertically
- press the ] (right bracket) key to Zoom in vertically
Press the:
- R key on your keyboard to Zoom out horizontally
- T key to Zoom in horizontally