Unfortunately, the Retina display is not nearly as impressive when it's been beaten and broken, but it is still impressively thin.

The glued layers are about 1.5 mm thick, and that includes the metal mounting plates.

We need to clarify this before continuing with the teardown; Apple did not design and build a 1.5 mm thin LCD panel. They did, however, do something exceptional with the design of this display: rather than sandwich an LCD panel between a back case and a front glass, they used the aluminum case itself as the frame for the LCD panel and used the LCD as the front glass.

TL;DR: The entire display assembly is an LCD panel.