Have you ever noticed that as you approach a horse, it appears to raise its head in a way that seems aggressive? In fact, the horse is not usually showing aggression, but rather is raising its head to see you. The lens in the eye of a horse does not have the ability to change shape as in the human eye. Instead, the back of the eye (the retina) is curved in an elliptical shape so that the straight-line distance from the front of the eye to the retinal surface depends on where the light is hitting the retinal surface. The result is that when a horse is trying to view objects up close it must lift its head in such a way that it uses the upper portion of its retina. More distant objects are viewed using the central portion of the retina in much the same way as a person who is presbyopic uses bifocal lenses to view both objects near and far.
(a) Given the information provided in Figure P24.78, determine the near-point distance for the horse. The near point distance is the shortest object distance for which the eye is able to focus.
(b) For a typical horse, estimate the distance from its eye to the tip of its nose. Using this estimate, does your answer to part (a) seem reasonable? Explain.