A pair of pinhole glasses, dating back to the 8th century, was found in a tomb along the Silk Road. Pinhole glasses have a series of pinhole-sized perforations in an otherwise opaque sheet of plastic. Each perforation only allows a very narrow beam of light to go through into the eye. The narrowness of the light beam means that the blur circle on the retina is much smaller than it would be if the peripheral light rays were also allowed to enter the eye and therefore the image is much clearer. They focus vision while they are on and are useful in that they can correct any refractive error – long sight, short sight, and presbyopia. The main drawback is that they cut down the amount of light going in to the eye, so they can’t really be used at night, but they can be helpful, for example, on the beach instead of having to buy prescription sunglasses.