of parallel strips of cylindrical lenses are imprinted in certain shapes, which separate the views seen by each eye in these areas, similarly to a hologram. Without stereopsis, the image looks only like a field of random dots, but the shapes become discernible with increasing stereopsis, and generally consists of a cat (indicating that there is ability of stereopsis of 1200 seconds of arc of retinal disparity), a star (600 seconds of arc) and a car (550 seconds of arc). To standardize the results, the image should be viewed at a distance from the eye of 40 cm and exactly in the frontoparallel plane. While most random dot stereotest like the Random Dot "E" Stereotest or TNO-Stereotest will require specific spectacles for testing (i.e. with polarized or red-green glasses), the Lang-Stereotest works without the use special spectacles, thereby facilitating the use in young children. Contour stereotests Examples of contour stereotests are the Titmus stereotests, the most well-known example being the Titmus fly stereotest, where a picture of a fly is displayed with disparities on the edges. The patient uses a 3-D glasses to look at the picture and determine whether a 3-D figure can be seen. The amount of disparity in images vary, such as 400-100 sec of arc, and 800-40 sec arc. Deficiency and treatment Deficiency in stereopsis can be complete (then called stereoblindness) or more or less impaired. Causes include blindness in one eye, amblyopia and strabismus. Vision therapy is one of the treatments for people lacking in stereopsis. Vision therapy will allow individuals to enhance their vision through several exercises such as by strengthening and improving eye movement. There is recent evidence that stereoacuity may be improved in persons with amblyopia by means of perceptual learning (see also: treatment of amblyopia). In animals There is good evidence for stereopsis throughout the animal kingdom. It occurs in many mammals, birds, reptiles, amphibia, fish, crustaceans, spiders, and insects. Stomatopods even have stereopsis with just one eye. See also Computer stereo vision Epipolar geometry Horopter Orthoptics Pupillary distance Vectograph References Bibliography Julesz, B. (1971). Foundations of cyclopean perception. Chicago: University of Chicago Press Steinman, Scott B. & Steinman, Barbara A. & Garzia, Ralph Philip (2000). Foundations of Binocular Vision: A Clinical perspective. McGraw-Hill Medical. . Howard, I. P., & Rogers, B. J. (2012). Perceiving in depth. Volume 2, Stereoscopic vision. Oxford: Oxford University Press. Cabani, I. (2007). Segmentation et mise