Whatever the reasons, the fact is that considerable progress had already been made in both catoptrics, the study of reflected light, and dioptrics, the study of refraction.    From Wordnik.com.  [Dictionary of the History of Ideas] Reference

The law of reflection was known as early as the time of Euclid, about 320 b.c., and to this geometrician was attributed, although probably erroneously, a "Treatise on Mirrors", in which the principles of catoptrics were correctly set forth.    From Wordnik.com.  [The Catholic Encyclopedia, Volume 12: Philip II-Reuss] Reference

30 This case contradicts a received principle in catoptrics.    From Wordnik.com.  [A Essay Towards a New Theory of Vision] Reference