For many people, the day only gains contours with the morning grip to the glasses, the view is sharpened. But how do glasses actually work and what exactly does a spectacle frame consist of? Normal-sighted eyes have no problem seeing objects sharply, both near and far. In normal-sighted eyes, the lens focuses the light rays entering through the pupil precisely so that they meet on the retina inside the eye. The lens itself is flexible up to a certain range and can thus compensate for minor visual defects as well as different distances. If the lens cannot provide this focusing of light on the retina, the receptors can only transmit a blurred image.
Nearsightedness and farsightedness
All nearsighted people can see near objects impeccably sharp – but distant ones only inaccurately. This is due to the not quite exact “construction” of the nearsighted eye: this is either a little too long and the lens focuses the incident light rays already before they fall on the retina in the back of the eye. Or the refractive power of the lens is not ideal. As a result, the image hitting the retina is slightly out of focus.
The opposite is true for the farsighted eye. This sees well at a distance, but has problems at close range, typically when reading. The reasons: Either the refractive power of the lens is not ideal – or the eye has grown a little too short. As a result, the lens does not focus the light exactly on the retina, but a little later. The image information hitting the retina is blurred.
What does eyeglasses do?
The single vision glasses in front of the eye cause additional bundling of light (in case of farsightedness) or scattering (in case of nearsightedness) with the result that the light rays meet exactly in the center of the retina. The result: a sharp look.
The eyeglass frame
Compared to the lenses, a spectacle frame actually seems quite simple at first glance: a frame, two temples, a nose pad, done? Far from it. There’s a lot of engineering know-how and creativity in eyeglass frames, too. This starts with the choice of the right material: steel? Sheet metal? Titanium alloys? Plastic? Horn? Or a combination?
The possibilities for variation are almost endless, but so are the difficulties that need to be considered when designing eyeglass frames. After all, not every type of material can simply be combined with every other. Once these technical problems have been solved, there are the different requirements that the wearer places on his or her glasses. These are highly contradictory: the model should be chic, yet lightweight, flexible, skin-neutral, sweat-resistant – and best of all, super-affordable.
Almost anything is possible: The engineers’ answer to the demand for “flexible temples,” for example, can then be either inexpensive (spring hinge) or elegant (highly flexible metal alloy). And whether a pair of glasses for allergy sufferers is made of allergy-free materials or is merely thickly coated with lacquer that ensures compatibility also has an impact on price and appearance.
Eyeglasses: constantly evolving
The beauty of it is that new manufacturing methods and materials are constantly entering the market, allowing designers to keep reinventing eyewear. Whereas a few years ago flexible, bendable metal was quite in demand, today the trend is once again moving more towards plastic – but this with the same material properties as introduced in metal eyewear. What seemed impossible until a few years ago is now already available for purchase from opticians.
