  The analysis of ring images produced by muons in an Imaging Atmospheric
Cherenkov Telescope (IACT) provides a powerful and precise method to calibrate
the IACT optical throughput and monitor its optical point-spread function
(PSF). First proposed by the Whipple collaboration in the early 90's, this
method has been refined by the so-called second generation of IACT experiments:
H.E.S.S., MAGIC and VERITAS. We review here the progress made with these
instruments and investigate the applicability of the method as the primary
throughput calibration method for the different telescope types forming the
future Cherenkov Telescope Array (CTA). We find several additional systematic
effects not yet taken into account by previous authors and propose several new
analytical methods to include these in the analysis. Slight modifications in
hardware and analysis need to be made to ensure that such a calibration works
as accurately as required for the CTA. We derive analytic estimates for the
expected muon data rates for optical throughput calibration, camera pixel
flat-fielding and monitoring of the optical PSF. The achievable statistical and
systematic uncertainties of the method are also assessed.
