Internal Sunglasses

Some birds appear to have sunglasses

Although I myself did not have to wear glasses (except perhaps sunglasses) until I turned 55, millions of people on Earth may view this simple ‘tool’ to improve the resolving power of their eyes as one of the greatest inventions ever made. Photographers, microscopists, and opticians can tell you that the aperture of an optical system not only controls the amount of light admitted (and thus the brightness of the image you see) but also the resolving power of the system.