Summarizing and systematizing these observations, we can say that for a ray that enters the
lens at the center, where the surfaces are parallel, the sum of the two deflection angles is zero.
Since the total deflection is zero at the center, it must be larger away from the center.Page 833, problem 31:
Normally, in air, your eyes do most of their focusing at the air-eye boundary. When you swim
without goggles, there is almost no difference in speed at the water-eye interface, so light is not
strongly refracted there (see figure), and the image is far behind the retina.
Goggles fix this problem for the following reason. The light rays cross a water-air boundary
as they enter the goggles, but they’re coming in along the normal, so they don’t get bent. At
the air-eye boundary, they get bent the same amount they normally would when you weren’t
swimming.