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The retina is the screen of cells at the back of your eye onto which your brain and eye lens try to project the image at which you are looking. If the sharp image falls short of the retina, you can only focus well on near objects (short-sightedness). If it falls beyond the retina, you can only focus well on distant objects (long-sightedness).

Long-sightedness
As we grow older, the muscles which control the focusing of the eye weaken and tire more easily and, despite their best efforts, the brain and lens project the sharp image beyond, rather than on, the retina. Most people start to get long-sighted at around forty years old. Looking through the tiny pinholes forces the eye muscles to exercise. Just 15-20 minutes a day brings a noticeable improvement within a couple of weeks.

The ‘blur circle’
The greater the error in focusing, the larger the amount of blur around the image - technically referred to as the ‘blur circle’. The greater the blur circle, the more out of focus the image you see. Conventional opticians recommend the use of corrective lenses which bring the image back onto the retina. This practice encourages the eye to be lazy, which is why people generally end up having to increase the strength of their prescription at regular intervals.

The screen of pinholes on your pinhole glasses reduces the effective aperture of the eye (the hole in your eye through which light passes) from that defined by the iris to that defined by the pinhole. This has the effect of reducing the blur circle proportionately (in the same way as how more of the image seen through a camera’s lens is in focus the more you reduce the aperture of a camera). The reduced blur circle makes it easier for the brain to recognise what to do in order to focus the image. Eventually, with practice, your brain re-learns how to focus at that distance. With regular practice, your brain and eye work more efficiently together and their ability to focus your eyes becomes more flexible.

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More about pinhole glasses

Frequently asked questions
How to use pinhole glasses
The history of pinhole glasses
Dr. Peter Mansfield's take on pinhole sunglasses
Bates Method Store's take on pinhole glasses
Some eye exercises
Pinhole glasses sight benefit diagrams

 

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