An optical mouse comprises a housing, an optics module, and a replaceable contaminant barrier. The housing has a surface with an optical window. The optics module includes a light source disposed within the housing and configured to direct light out of, and receive light in, through the optical window....http://www.google.co.uk/patents/US7166831?utm_source=gb-gplus-sharePatent US7166831 - Optical mouse with replaceable contaminant barrier
