Defendants and witnesses shall not be subjected to physical restraint while in court unless the trial judge has found such restraint reasonably necessary to maintain order. If the trial judge orders such restraint, he shall enter into the record of the case the reasons therefor. Whenever physical restraint of a defendant or witness occurs in the presence of jurors trying the case, the judge shall upon request of the defendant or his attorney instruct the jury that such restraint is not to be considered in assessing the proof and determining guilt.