The invention relates to an optical instrument, in particular an endoscopic instrument, with a housing, containing at least one optical system and a hygroscopic substance, and in which an eyepiece is detachably secured to the housing. In order to design an optical instrument of the aforementioned type in such a way that the hygroscopic substance can be integrated easily and safely into the housing, the invention proposes that the hygroscopic substance should be imbedded in a moldable matrix material and that the matrix material caulked with the hygroscopic substance can be replaceably inserted in the eyepiece.