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 claimed to be a clearer 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. This leads to double vision (objects having doubled edges) around the rim of each hole the eye is not focussing on, which can make the overall image disturbing and tiring to look at for prolonged periods of time. Unlike conventional prescription glasses, pinhole glasses produce an image without the pincushion effect around the edges (which makes straight lines appear curved). While pinhole glasses are claimed to be useful for people who are both near- and far-sighted, they are not recommended for people with over 6 diopters of myopia. Additionally, pinhole glasses reduce brightness and peripheral vision, and thus should not be used for driving or when operating machinery .
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