From your menu bar, I'm seeing that you're running Mac OS 10.12 Sierra. CS5's really old - from way back in April, 2010. CS5 is not intended to be compatible with Sierra at all. Adobe recommends CC2017 (they don't even support CC2015 in Sierra). Many people can't even get CS5 to boot in this version of the OS. So - what you're experiencing is a video card anomaly (among other things). The only way to resolve this would be to upgrade your Photoshop to CC2017 (which, if you just want their digital photography package is a reasonable $10/month (Lightroom and Photoshop | Adobe Creative Cloud Photography plan)
OR, you can buy a software emulation app - like Parallels. Every version of the Mac OS since OS 10.7 can be run in emulation using Parallels on the Mac.
I dont know you this will help you or not but still have a look in this post - https://feedback.photoshop.com/photoshop_family/topics/i_dont_like_the_way_the_zoom_tool_w orks_in_photoshop_cs5_how_do_i_change_it_back_to_the