YAZRO

Focusing on the World In a camera the image is brought into focus by moving the lens forward and back   so that the distance between the lens and the film is modified. In human beings   the image is focused by muscles that actually change the shape of the lens, making   it flatter when objects are far away and round and fat when objects are close. The   dog can’t change the shape of its lens as much as humans can, but there is some   suggestion that, like cats, dogs have a set of muscles that can make the eye slightly   longer or shorter to help focus the image. How efficiently the lens changes focus   has a direct effect on the visual acuity of dogs. If the eye can focus the image exactly at the level of the retina, you will get the   best visual acuity that the eye’s optics allows (this most desirable state is   technically called “emmetropia”). If the image comes to a focus too soon (that is,   before it reaches the retina...