Читать книгу Essentials of Veterinary Ophthalmology - Kirk N. Gelatt - Страница 143

Many associate stereopsis with predatory behavior, as depth vision is required to pounce on prey with precision. However, stereopsis is just as important for the prey that uses it to distinguish between a camouflaged predator and its surroundings. Though monocular stereopsis is possible thanks to various visual cues including grain, texture, brightness, contour, size, and relative motion, in most cases stereopsis is the result of binocular vision, and the extent to which the visual fields of the two eyes overlap. In addition, optimal stereopsis requires normal visual function and refraction, oculomotor control to maintain fixation, and sensory and neuronal mechanisms to extract and process important visual cues.

Figure 2.17 (a) The visual field of the horse showing a frontal binocular field (65°) comparable to that of a dog but with much larger panoramic monocular fields (each spanning 146°) and a very small posterior blind area (3°). (b) Visual field of a cat showing a large frontal binocular field (140°) with relatively small monocular fields (each 30°) and a relatively large posterior blind area (160°). (c) Monocular and binocular visual fields in a typical mesocephalic dog. The dog has a modest frontal binocular visual field (60°) with relatively large monocular visual fields (each 90°) and a posterior blind area of approximately 120°.