This allowed them to travel in an environment where light was coming from every direction and all contours were missing. The clarity given by the pinholes is due to the fact that the blur circle on the retina is reduced. The moment a pinhole is introduced in front of the eye a much narrower parallel pencil of light comes through the hole. The light again goes through the focal point F resulting in a much smaller blur circle on the macular area. People with both close and distant blur, and astigmatism, are able to use pinhole spectacles as T-glasses while they're in the process of improving their sight through natural means.
Pinholes have some disadvantages.
They are not useful at night nor recommended for driving. They reduce peripheral vision and most driving laws require compensatory lenses. One of their greatest advantages is that they are not prescriptive. Almost everyone, no matter what their error of refraction, sees clearly through the holes. In addition, they encourage saccadic motion.