Geodesic acoustic modes (GAMs) represent the oscillating counterpart of the zonal flow and can affect transport with their interaction on turbulence eddies. GAMs have been observed in many experiments and modelled under different conditions, but because of their variety of characteristics, we do not yet have a complete picture of their dynamics. Optical methods, it has been demonstrated [Palermo et al. 2020 ] can be efficiently used to describe and predict several characteristics of these radial structures that can be interpreted as waves propagating in the space-time. By using eikonal theory we investigate several characteristics of GAMs focusing in particular on their periodic modulation and intermittent behavior that appears as a common characteristic observed in the experiments. Theoretical results obtained in this work are supported by gyrokinetic simulations for several equilibria. Implications on condition of existence and GAM dynamics in different plasma scenario such as L- and H- mode with particular attention during the L-H transition are discussed.