We are interested in understanding the compound eyes of arthropod animals such as crabs and insects and are using CT as one of our approaches. Unlike our eyes, compound eyes have many hundreds of tiny lenses, with each light-receptive unit of the eye pointing in different directions to provide a very wide field of view for the animal. In an attempt to find a new way to reconstruct the visual field of arthropod eyes, we have recently produced a micro-CT scan (499 x 488 x 930 pixels) of a crab eye. We now need to reconstruct the direction in space of each light receptor cell within the. This requires us to mark each receptor with two 3D points in order to work out its longitudinal, axial, direction. An efficient software tool is needed for data extraction and storage, ideally as a module/extension package for one of the freely available 3D viewer software packages. A follow up project could provide software to reconstruct an eye's field of view, mapping the 3D directions of each light receptor onto a sphere representing the space around an animal. Such software would have a major impact in visual ecology.