At present, optical polymers are increasingly replacing glass in several applications, including the field of ophthalmic lenses. In the present work, protecting and optical SiOxCy:H coatings have been deposited by Plasma Enhanced Chemical Vapor Deposition onto polymeric substrates at low temperature from hexamethyldisiloxane (HMDSO) and oxygen precursors. The best mechanical properties are obtained for composition graded SiOxCy:H layers, in which the O-2/HMDSO ratio is varied during deposition. The optical properties of the protective layers, in particular the spectral behavior of the refractive index and extinction coefficient, have been calculated from the transmittance and reflectance spectra. Elastic Recoil Detection Analysis was used to obtain information about the elemental composition of the layers as a function of the deposition parameters. (c) 2006 Elsevier B.V. All rights reserved.