Reexamination of an Airman
A medical certificate holder may be required to undergo a reexamination at any time if, in the opinion of the Federal Air Surgeon or authorized representative within the FAA, there is a reasonable basis to question the airman's ability to meet the medical standards. An Examiner may NOT order such reexamination.
Cited From FAA Aviation Medical Examiner's Guide Vol V (3 Apr 06), p.13