The user looks through these small holes in the material.
These holes have the effect of reducing the part of the light rays coming from a viewed object, thereby contributing to improving vision acuity.
The figure below is a schematic representation of a bundle of light rays coming from an object in front of a myopic (nearsighted) eye.
Improper refraction, or "bending", of the outermost rays (dotted lines) in that bundle of light by the eye is a cause of refractive errors such as myopia, hyperopia (farsightedness), presbyopia (diminished focusing range with age) and astigmatism. Pinhole glasses can bring about clearer vision in all these conditions.
Referring to the figure and the representation of a pinhole in front of the eye: by the lens blocking the outermost rays and allowing only the central rays (solid lines) to pass into the eye, a refractive error in the eye's lens or cornea is not as pronounced. In other words, the eye's pupil may be wide open, but only its central portion is receiving light.
The improvement in visual acuity in this case can be considerable.
This principle, employed in Pinhole glasses, is found in many other applications, including the well-known pinhole camera, used widely in photography in the past.
An easy way to demonstrate this effect yourself is to make a fist, and put it up to one eye, while closing the other eye.
Open your fist just enough to create a small hole to look through.
If your eye has a refractive error, you should see more clearly this way.
A similar vision improvement occurs "naturally" when we squint to see somewhat more clearly.
The squinting eyelids block the rays that would normally enter the top and bottom of the pupil, in a manner similar to that shown in the figure above. However, since squinting doesn't serve to cut off rays entering the sides of the pupil, these rays may still contribute to a blurred image.
By looking through Pinhole glasses, instead of squinting, peripheral rays are blocked from all sides.
For those in their 40's and 50's-and older
- Presbyopia (inability to focus close) develops during these years. Pinhole glasses provide a simple and inexpensive alternative for reading or other close work.
- Some bifocals or trifocals are designed to provide a clear image only at fixed distances. Pinhole Glasses provide an improved image at ALL distances. In many applications, such as alternating between watching TV and reading, they can easily take the place of relatively expensive prescription lenses.
- Multi-focal lenses provide a continuously variable focal curve that is intended to allow good vision at all distances. In reality, distortion on either side of the multi-focal center line can be considerable and may be too great for comfortable use. Pinhole Glasses do not have this problem.
- Some people with cataracts see better through Pinhole Glasses. A cataract is one or more opacities in the eye's lens that do not allow the light to pass through properly, but instead cause it to scatter. By blocking off the peripheral rays, Pinhole glasses aid to reduce some of this scattering and thereby provide a sharper image.