Over 60Yrs Driving License Requires Medical Test. Details?

Not mentioned in the driving forums that I have seen, and only when I got to the Traffic HQ in Pt. Louis with every other document, is  that they require of foreign drivers over 60 years have a medical "fitness to drive" test. Which I was told in a friendly way "any  doctor can do"


What are the details of this test, what it involves? I have heard it is quite extensive?