  In this paper we study the light bending caused by a slowly rotating source
in the context of quadratic theories of gravity, in which the Einstein--Hilbert
action is extended by additional terms quadratic in the curvature tensors. The
deflection angle is computed employing the method based on the Gauss--Bonnet
theorem and working in the approximation of a weak lens; also, we assume that
the source and observer are at an infinite distance. The formalism presented is
very general and applies to any spacetime metric in the limit of weak
gravitational field and slow rotation. We find the explicit formula for the
deflection angle for several local and nonlocal theories, and also discuss some
phenomenological implications.
