<P> The dog's visual system has evolved to aid proficient hunting . While a dog's visual acuity is poor (that of a poodle's has been estimated to translate to a Snellen rating of 20 / 75), their visual discrimination for moving objects is very high . Dogs have been shown to be able to discriminate between humans (e.g. identifying their human guardian) at a range of between 800 and 900 metres (2,600 and 3,000 ft); however, this range decreases to 500--600 metres (1,600--2,000 ft) if the object is stationary . </P> <P> Dogs can detect a change in movement that exists in a single diopter of space within their eye . Humans, by comparison, require a change of between 10 and 20 diopters to detect movement . </P> <P> As crepuscular hunters, dogs often rely on their vision in low light situations: They have very large pupils, a high density of rods in the fovea, an increased flicker rate, and a tapetum lucidum . The tapetum is a reflective surface behind the retina that reflects light to give the photoreceptors a second chance to catch the photons . There is also a relationship between body size and overall diameter of the eye . A range of 9.5 and 11.6 mm can be found between various breeds of dogs . This 20% variance can be substantial and is associated as an adaptation toward superior night vision . </P> <P> The eyes of different breeds of dogs have different shapes, dimensions, and retina configurations . Many long - nosed breeds have a "visual streak"--a wide foveal region that runs across the width of the retina and gives them a very wide field of excellent vision . Some long - muzzled breeds, in particular, the sighthounds, have a field of vision up to 270 ° (compared to 180 ° for humans). Short - nosed breeds, on the other hand, have an "area centralis": a central patch with up to three times the density of nerve endings as the visual streak, giving them detailed sight much more like a human's . Some broad - headed breeds with short noses have a field of vision similar to that of humans . </P>

Where is the tibia located on a dog