stereoscope An

stereoscope An

instrument that allows targets to be presented independently to the two eyes. The separation of the targets is produced either by tubes, a septum, or an arrangement of mirrors. Stereograms are the targets used with a stereoscope. Stereoscopes are used to test and train binocular fusion and stereopsis, evaluate suppression and view images in three dimensions.
Brewster's stereoscope An Stereoscope consisting of two tubes separating the two fields of view and convex lenses. The distance between the tubes can be adjusted to suit the viewer's PD. Syn. lenticular stereoscope; Brewster-Holmes stereoscope (although this instrument uses a septum to separate the two visual fields, a sliding stereogram holder and decentred convex lenses, usually +5.25 D, to produce BO prisms) (Fig. S14). See Telebinocular.
Brewster-Holmes stereoscope An See Brewster's stereoscope.
lenticular stereoscope An See Brewster's stereoscope.
Pigeon-Cantonnet s . A stereoscope consisting of three black cardboard leaves attached together as in a book, with a plane mirror placed on one face of the middle leaf and targets on the other two leaves. The subject places the central leaf as a septum and one eye sees one target directly while the other eye sees the other by reflection in the mirror. The angle of convergence may be controlled by the angle between the leaves. This instrument is often used in visual training as well as in orthoptics.
variable prism stereoscope An A stereoscope incorporating two Risley prisms and a septum positioned so that each eye sees one half of a stereogram card which can be moved to and fro from the eyes in the median plane of the head. To maintain the normal relationship between accommodation and convergence at a given fixation distance, BO prisms are adjusted before each eye. This instrument is particularly well suited to measure and train fusional reserves of convergence and divergence. See rotary prism.
Wheatstone s . See Wheatstone amblyoscope." >Fig. S14 Principle of the Brewster-Holmes stereoscope (S, septum; A and B, stereograms; O, optical centre of the convex lenses decentred to produce BO prisms; V, fused images formed by the lenses)