Читать книгу Essentials of Veterinary Ophthalmology - Kirk N. Gelatt - Страница 144

If an object is located in the plane of fixation of both eyes, it is viewed with the same angle by both eyes (Figure 2.18). However, objects outside the binocular plane of fixation are viewed with a slightly different angle by each eye, resulting in disparate images. The visual angle can serve as a “range finder.” An object is deemed close if the projection lines from both eyes intersect before the plane of fixation, thus triggering a converging oculomotor response; for a distant object, the projection lines intersect beyond the plane of fixation, serving as an oculomotor stimulus for divergence.

Figure 2.18 Binocular disparity and the perception of stereoscopic depth. The green diamond is on the plane of fixation of both eyes. It is therefore seen at the same angle by both eyes and projected onto both foveas (fv). Both the purple circle and red square are outside the plane of fixation. Therefore, they are viewed at different angles by both eyes, and projected onto disparate (but corresponding) retinal regions. The purple circle is closer than the object of fixation (the green diamond) and therefore the projection lines from both eyes intersect before the plane of fixation. The red square is further away, and the projection lines from both eyes intersect after the plane of fixation. The α angles of these projection lines, and their intersection, serve as range finders in stereoscopic depth detection.