In this work we present a new optical guided mode technique which is used to monitor small perturbations to the director twist profile in a conventional liquid crystal cell. The cell is filled with nematic liquid crystal E7 which is homogeneously aligned using rubbed polyimide. Twist distortions are induced via the application of weak in-plane electric fields. Careful analysis of these distortions allows both the twist elastic constant, k22, and the azimuthal anchoring strength, Wa, of the cell to be determined.