A method for optically detecting flow movements in liquid and/or gaseous media, wherein in this method - a measuring volume is defined in the medium and at least one measuring plane is defined within the measuring volume, and - particles moving in the extension of the measuring plane are optically detected, in that - the measuring plane is exposed to light and is illuminated in at least one detection area from the one side of the measuring plane, that is from a lighting side, by means of a light beam bundle of parallel light beams of a lighting unit, - scattered light is generated by means of particles within the detection area of the measuring plane, - the light beam bundle is directed through the detection area of the measuring plane and its transmitted light proportion is directed laterally past at least one light guiding element, wherein scattered light or at least a portion thereof, radiating as a pre-light scattering to a pre-light scattering side facing one of the lighting sides, is guided through the at least one light guiding element to the image capturing plane of a camera, wherein the light guiding element comprises at least one scattered light entry end facing the detection area of the measuring plane and is provided with a transparent window element for the scattered light, and wherein the lighting unit comprises at least one light beam bundle exit end facing the detection area of the measuring plane and assigned to the scattered light entry end, - the camera captures a sequence of images of the detection area, and - an image sequence is used to determine a motion vector with regard to at least one particle by means of computer-aided image evaluation. - a measuring volume is defined in the medium and at least one measuring plane is defined within the measuring volume, and - particles moving in the extension of the measuring plane are optically detected, in that - the measuring plane is exposed to light and is illuminated in at least one detection area from the one side of the measuring plane, that is from a lighting side, by means of a light beam bundle of parallel light beams of a lighting unit, - scattered light is generated by means of particles within the detection area of the measuring plane, - the light beam bundle is directed through the detection area of the measuring plane and its transmitted light proportion is directed laterally past at least one light guiding element, wherein scattered light or at least a portion thereof, radiating as a pre-light scattering to a pre-light scattering side facing one of the lighting sides, is guided through the at least one light guiding element to the image capturing plane of a camera, wherein the light guiding element comprises at least one scattered light entry end facing the detection area of the measuring plane and is provided with a transparent window element for the scattered light, and wherein the lighting unit comprises at least one light beam bundle exit end facing the detection area of the measuring plane and assigned to the scattered light entry end, - the camera captures a sequence of images of the detection area, and - an image sequence is used to determine a motion vector with regard to at least one particle by means of computer-aided image evaluation. - the measuring plane is exposed to light and is illuminated in at least one detection area from the one side of the measuring plane, that is from a lighting side, by means of a light beam bundle of parallel light beams of a lighting unit, - scattered light is generated by means of particles within the detection area of the measuring plane, - the light beam bundle is directed through the detection area of the measuring plane and its transmitted light proportion is directed laterally past at least one light guiding element, wherein scattered light or at least a portion thereof, radiating as a pre-light scattering to a pre-light scattering side facing one of the lighting sides, is guided through the at least one light guiding element to the image capturing plane of a camera, wherein the light guiding element comprises at least one scattered light entry end facing the detection area of the measuring plane and is provided with a transparent window element for the scattered light, and wherein the lighting unit comprises at least one light beam bundle exit end facing the detection area of the measuring plane and assigned to the scattered light entry end, - the camera captures a sequence of images of the detection area, and - an image sequence is used to determine a motion vector with regard to at least one particle by means of computer-aided image evaluation.