I was disappointing when I first tried my new Google CardBoard kit with my 5.5 inch OnePlus One. It had a severe double vision problem that made it impossible to use.
Even though the Cardboard kit that I bought was supposedly the “Large” model, the kit seemed to work fine with smaller phones but not the OnePlus.
I found some solutions online but none of them really worked, so finally I came up with my own solution, which solved the cardboard double vision problem completely with my large OnePlus running Android 5.1
1. Go to the Settings -> Display.
2. Change the LCD density from the default 480 DPI to 360.
3. The phone will soft reboot.
4. Try Cardboard now, the problem is solved!