It has not sense to install a `spyhole´ on a glass door, and it is more ridiculous to install two big ones, unless both circles are fixed to the door handle and its function improve the structural strength between the glass and the handle.
The stainless steel door handle is designed for glass within thickness from 8mm to 12mm. The door handles (two, one at each side of the door) and the glass are fixed using two circles that maximize the contact surface and resistance between both. That allows to be mounted on bigger and heaviest glass doors. The rounded fixations play with humor and sarcasm the fact of installing an eye-hole on a glass door, of course, if you want some privacy better do not install a transparent door.