Pinhole glasses, also called stenopeic glasses, are eyeglasses with lenses that consist of many tiny holes filling an opaque sheet of plastic. These “pinholes” block indirect rays from entering the eye, thus preventing them from distorting your vision. While this does not actually improve the focusing ability of the eye, it does reduce the size of the blur circle on the back of the retina, so reasonably clear vision may be achieved.
How They Work
We have all experienced this phenomenon by squinting our eyes to improve vision. Squinting achieves the same thing. It reduces the size of the de-focus light rays that land on the retina. You can do the same thing by making a small circle with your thumb and your pointing finger and looking through it. Of course, those of us that do not have any significant vision problems will not notice much difference. However, people that wear corrective lenses will notice an improvement, sometimes a significant improvement.
If you try on a pair of pinhole glasses, you may actually notice an improvement in your vision. However, while wearing the pinhole glasses, vision is quite obstructed by the black spaces around the pinholes. There seems to be a trade-off in the clarity of vision compared to the amount light being let through. If you make the holes infinitely small, vision will be better, but the amount of light is so restricted that the quality of vision is horrible.
Pinhole glasses are mainly used by eye care specialists as a diagnostic tool. Many eye doctors use an occluder, an instrument used to cover one of your eyes while reading the eye chart. On one end, the occluder is solid. On the other end, the occluder has many tiny pinholes.
Sometimes doctors use this to quickly see the potential of your vision. For example, if someone comes in for an office visit for an eye infection and they can only read the 20/70 size of letters on the eye chart, the doctor will wonder, “Is this person’s vision 20/70 because of the eye infection, or could part of that decreased vision be due to a being nearsighted?” To quickly find out if that patient’s vision could potentially see better than 20/70, the doctor may perform a “pinhole” visual acuity test. If the patient looks through the pinholes and reads 20/25, then it could be assumed that most of the decreased vision is not due to the infection, but rather some type of uncorrected vision problem. It may be safe to assume that the infection may be reducing the vision only slightly.
The doctor may not have time to find out what type of the prescription the patient might need, because the person may have come in only to have the infection treated. Therefore, the pinhole test is a very quick way to find out more information about a person’s eye condition. Pinhole glasses are used in other ways to evaluate corneal distortion and cataracts.