For the medical community: Is there any device to measure the actual thickness of the cornea?

And if there isn't, then what formula does laser eye surgery use to determine amount of cornea to take off?

Please cite sources or your expertise.

There are several ways to measure corneal thickness: the process itself is called "pachymetry." The most common instrument is a pachymeter, which measures corneal thickness through brief contact with the eye, as seen here: http://vision.about.com/od/eyeexaminatio... It takes only seconds and is painless. Non-contact intruments exist as well (see last link below).

Lasik can be unsafe for people with thin corneas, not necessarily because of the amount "taken off" (it's actually "reshaped") but because the flap that is cut during Lasik surgry must be thick enough that the flap won't detach.

The formula used to determine whether a person is a candidate for one of these surgeries boils down to simple addition/subtraction of te patient's corneal thickness, the required size of the flap, and the amount of cornea to be removed to obtain the necessary level of correction (the worse your eyes are, the more cells will need to be removed to correct them).

Per the first link below, the size of the flap should be at least 160* microns and the amount of cornea remaining after surgery should be 250* microns. So, for example, if a patient's corneal thickness was 500 (which is thin -- normal corneas are about 500 microns), no more than 90 microns could be removed safely. To put it another way: if MORE than 90 microns would need to be removed to correct that patient's vision, s/he would likely be deemed ineligible for Lasik surgery. (There are other types of laser vision correction that don't require creating a flap; this person could be eligible for PRK, Lasek, or Lasik with IntraLase)

*Some doctors are more conservative than others about the thickness of the flap and the amount of cornea to remain intact after surgery.

Yes - it's called a pachymeter. See the sources for more info.