Depends. Usually an optical coherence tomogram is performed annually, but exceptions apply, particularly if a significant clinical status of the eye has changed and a measurement is needed. An example in inflammatory glaucomas is macular edema, where an oct of the macula is performed, or if the optic nerve head has edema or significantly more notching or thinning. Changes in oct data useful for treatment.
Not often. Oct is a nice adjunct to the standard testings of the pressure and visual field. After the first screening oct, it should only be done when there is significant changes in one of the other indices. If your eyedoc is doing them often, that is churning the system for profit and will not be of medical benefit.