In this paper the formal analogue between deflections of light due to the optically inhomogeneous medium and due to gravitational field is disscussed. It has been shown that there exists a "relation of equivalence" about these two kinds of deflection. In the last part of this paper, an attempt was made to modify the equation of the light ray geodesies in the gravitational field with the consideration of the effect due to the optically inhomogeneous medium. Essentially this modification is to transform the gravitational space-time metric tensor gaB to a new metric tensor gas which can apply both for the gravitational field and for the optically inhomogeneous medium.