For many people, the day wins contours only with the morning grip on the glasses, the view is sharpened. But how do eyeglasses actually work and what exactly does a spectacle frame consist of? Normal-sighted eyes do not have any problem viewing sharp objects both near and far. In normal-sighted eyes, the lens focuses the rays of light entering through the pupil just in such a way that they meet on the retina inside the eye. The lens itself is flexible up to a certain range and can thus compensate for smaller visual impairments as well as for different distances. If the lens can not afford this bundling of light on the retina, the receptors can only pass on a blurred image.
Myopia and hyperopia
All myopia can see close-up objects perfectly sharp - but only vaguely removed. This is due to the not very exact "construction" of the myopic eye: this is either a little too long and the lens bundles the incident light rays before they fall on the retina in the fundus. Or the refractive power of the lens is not ideal. As a result, the image incident on the retina is slightly out of focus.
The opposite is the case with the farsighted eye. This looks good on the distance, but has problems nearby, 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 incident on the retina is out of focus.
What causes glasses?
The single-vision goggles in front of the eye cause additional focusing of the light (in case of farsightedness) or scattering (in myopia), with the result that the light rays meet exactly in the center of the retina. The result: a keen eye.
The spectacle frame
Compared to the lenses, a spectacle frame seems to be quite simple at first glance: A frame, two brackets, a nose pad, finished? Not even close. Spectacle frames also contain a lot of engineering know-how and creativity. It all starts with choosing the right material: steel? Sheet? Titanium alloys? Plastic? Horn? Or a combination?
The possibilities of variation are endless, but so are the difficulties that must be considered in the spectacle conception. Because not every kind of material can be easily combined with each other. Once these technical problems have been solved, the different requirements that the wearer places on his glasses come about. These are highly contrary: Schick should be the model, while light, flexible, skin-neutral, sweat-resistant - and best super cheap.
Almost everything is possible: the engineers' response to, for example, the requirement of "flexible brackets" can then be either favorable (spring hinge) or elegant (highly flexible metal alloy). And whether glasses for allergy sufferers consists of allergy-free materials or is only thickly covered with varnish, which ensures compatibility, also affects price and appearance.
Glasses: steadily in development
The nice thing is that new production methods and materials are constantly pushing the market, allowing designers to reinvent the glasses over and over again. While flexible, pliable metal was in great demand a few years ago, today's trend is more towards plastic - but with the same material properties as the metal eyeglasses. What seemed impossible until a few years ago is already available to buy today at the optometrist.