  Given a point S and any irreducible algebraic curve C in P^2 (with any type
of singularities), we consider the caustic of reflection defined as the Zariski
closure of the envelope of the reflected lines from the point S on the curve C.
We identify this caustic with the Zariski closure of the image of C by a
rational map. Thanks to a general fundamental lemma, we give a formula for the
degree of the caustic of reflection in terms of multiplicity numbers of C (or
of its branches). Our formula holds in every case. We also give some precisions
about Pl\"ucker formulas.
