How the eye works

• Light enters through the cornea - a convex transparent membrane that covers the eyeball. Its curved shape allows light entering from different angles to be concentrated into a beam of light that enters the pupil.
• The pupil regulates the amount of light that enters the eye, and passes the beam of light into the lens.
• The lens focuses the beam of light through the vitreous humour and onto the retina near the back of the eyeball. The ciliary muscle controls the lens so to give it the right shape to enable exact focusing of the image on the retina.
• On reaching the retina, that is the part of the eye that is actually sensitive to light, it transmits the information to the optic nerve, which in turn sends the image to the brain.

Perfect vision in the unaided eye requires the eye lens to focus light rays from diverse angles into a single pinpoint directly on the retina at the back of the eye. For sufferers of refractive eye disorders, where the eye lens is too weak or the cornea or eyeball is misshapen, divergent light rays become focused in front of or behind the retina, casting an unfocused image onto the retina itself. This unfocused area of light is known as the 'blur circle'.

Pinhole glasses work by reducing the diversity of angles from which light rays can enter the eyes, allowing only direct light rays within a narrow angular path to strike the cornea. The lenses of pinhole glasses are perforated with an array of equally spaced minute holes of approx 1mm - 1.5mm in diameter. In contrast the average diameter of the pupil in normal daylight conditions is about 4mm. Each pinhole allows only direct rays through, and it is the amalgamation of these direct rays that make up a concentrated beam of light that enters the pupil. When this restricted light beam passes through the pupil and into the eye lens, the effects of any refractive eye disorders are reduced as the 'blur circle' on the retina is proportionally smaller. The resulting visual image is one of increased clarity, definition and brightness.

Pinhole glasses are based on the principle of natural reflexes as the same effect is achieved when you squint to try and see more clearly. Your eyelids close around the top and bottom of your eyes, filtering out light rays reaching your pupil from these angles. Only light from your central area of vision and to the left and right sides can now enter your eye. The image you see is often sharper with a greater depth of resolution, and is generally brighter as there is a narrower range of light levels to contrast against each other. Wearing pinhole glasses is of course much less stressful on the eye than squinting, and is far more efficient at blocking extraneous light rays to produce a sharper and brighter image on your eye.