Pinhole glasses, also known as stenopeic glasses, are eyeglasses with a series of pinhole-sized perforations filling an opaque sheet of plastic in place of each lens. Similar to the workings of a pinhole camera, each perforation allows only a very narrow beam of light to enter the eye which reduces the size of the circle of confusion on the retina and increases depth of field. In eyes with refractive error, the result is often a sharper image. However, a second effect may appear at the common bridge between each two adjacent holes, whereby two different rays of light coming from the same object (but each passing through a different hole) are diffracted back toward the eye and onto different places on the retina.