Pinhole Reading Glasses

Pinhole reading glasses, also known as stenopeic glasses from the Greek words for "little opening", are not made of glass at all but of an opaque substance such as metal or plastic. The user looks through any of the many small holes in the material. These holes have the effect of reducing the width of the bundle of diverging rays coming from each point on the viewed object. Normally, the full opening of the pupil admits light. It is the improper bending of the outermost rays in that pencil of light which causes refractive errors such as myopia, hyperopia (farsightedness), presbyopia (diminished focusing range with age) and astigmatism to be noticeable. Pinholes can bring about clearer vision in all these conditions. By blocking these peripheral rays, and only letting into the eye those rays which pass through the central portion of the pupil, any refractive error in the lens or cornea is not noticed as much. The pupil may be wide open, but only the central portion is receiving light.

Some limitations of pinhole glasses are that blocking some of the light makes it more important than usual to have good lighting on the viewed object, even though the sharper image greatly compensates for the diminished light. When looking at television this is not a problem since the set makes its own light. When reading, a good lamp should be provided nearby.

Another limitation is that peripheral vision is diminished, so they should not be used for driving or similar activities involving motion. As with any glasses, even sunglasses, they should not be used to stare at the sun, thinking that no harm can be done.

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