An optical microscope slide in a charged particle instrument such as an electron microscope or a focused ion beam instrument. Conventional microscope slides are not fit for use in an electron microscope as they are insulating and would thus charge when viewed in an electron microscope due to the impinging beam of charged particles. However, microscope slides exist that show a coating with a conductive layer of e.g. Indium Tin Oxide (ITO). These microscope slides are normally used for heating the object mounted on the slide by passing a current through the conductive layer. Experiments show that these microscope slides can be used advantageously in a charged particle instrument by connecting the conductive layer to e.g. ground potential, thereby forming a return path for the impinging charged particles and thus avoiding charging. The invention further relates to a charged particle instrument that is further equipped with an optical microscope.