  In a previous article concerning image distortion in non-perturbative
gravitational lensing theory we described how to introduce shape and distortion
parameters for small sources. We also showed how they could be expressed in
terms of the scalar products of the geodesic deviation vectors of the source's
pencil of rays in the past lightcone of an observer. In the present work we
give an alternative approach to the description of the shape and distortion
parameters and their evolution along the null geodesic from the source to the
observer, but now in terms of the optical scalars (the convergence and shear of
null vector field of the observer's lightcone) and the associated optical
equations, which relate the optical scalars to the curvature of the spacetime.
