A soft rubber gasket cushions the display against the lens assembly, and seals dust out of the clean-room optics chamber.
The lenses are glued in place in their frame, but with a bit of encouragement (e.g. some heat and a good push) they pop right out.
These are 14 mm thick conventional lenses, with no Fresnel stepping, and a smooth dome shape. That means the lenses are quite a bit thicker than the Fresnel lenses in the Vive and the hybrid Fresnel lenses of the Rift.