The cuvette (10) has two cuvette shells (12), over which a form area (14) for bringing polymerizable plastic is formed over a filling channel. A vent duct (42) is provided for air, which escapes during the filling of the form area. The vent duct includes a filter element (40), whose permeability for air changes, in particular reduces automatically, when it comes in connection with the polymerizable plastic. The filter element is made of open-pored plastics.
