It takes practice. [She's neutral. When you work with people who can see and manipulate microscopic detail...]

They are flexible lenses, shaped like small thin-walled bowls, that fit closely to the eyes. It's difficult to see if someone is wearing one, if it's well made.

Droptacs are slightly more obvious, since the eye seems slightly darker, but it's still easier to conceal than a pair of glareshades.