The caustic pattern which is formed by a concentrated load P acting on a half-plane of an optically anisotropic material is theoretically considered, and the method of determining the value of P by caustics for birefringent as well as optically inert materials is shown. The effect of initial curve γ₀ on the evaluation of P is experimentally studied. It is shown that the value of P determined from the caustic pattern is influenced by the radius of γ₀ when the dimension of γ₀ is less than half the thickness of the specimen. The reason for this phenomenon is discussed from two points of view, namely, the existence of three-dimensional stress and the effect of load distributed by the shape of the loading pin. Moreover, a technique for measuring the optical constants in caustics is proposed. These constants can be easily determined from the caustic pattern obtained by the concentrated load, and the validity of the technique is experimentally ascertained for several polymers such as Plexiglas, epoxy resin and polycarbonate. The absolute photoelastic coefficients and the photoelastic sensitivity of these materials are also obtained by this method.