Progressive lenses become a topic of discussion when people can no longer read labels in supermarkets and the numbers on their mobile phones become increasingly small. This type of defective vision starts from the age of 40 as the elasticity in the ocular lens decreases appreciably resulting in various points that are near and far no longer being able to be pictured alternately on the retina. The solution to this problem is either reading glasses or progressive glasses. The advantage of progressive glasses is that you don’t have to keep putting the glasses on and taking them off, you can see clearly at all distances with them on.
MANUFACTURE OF THE PROGRESSIVE GLASSES
The traditional manufacturing process of branded progressive lenses has a limit. Ten years ago, the complicated surface contours of a progressive surface were only able to be achieved using ceramic moulds. Liquid plastic is poured into these moulds in a casting process. This traditional method is still used by many manufacturers, but some distortions are not able to be remedied in this way.
In the meantime, a lot has changed in the manufacture of progressive lenses. The biggest lens manufacturers have switched to digital surfacing machines. This is a computer-controlled grinding and polishing process in which the surface of the glass is manufactured point by point using diamond tips. Thanks to this new manufacturing method, individual data of the person wearing the glasses can be utilised.
The distance between the pupils and the fitting height were always included in the requirements for clear vision. Other data cannot be used in analogue manufacture.
If, for example, a frame is not parallel to the face of the person wearing the glasses, the angle generated is important.
The curve of a frame can now be taken into account too. If the curve is significant, the field of vision shifts.
Another important parameter is the distance between the frame and the eye. If the glasses are further away from the eye and this is not taken into account, there are fewer usable areas in which the person can see.
Every single day, your head and your eyes made more than 100,000 movements. Some people move their heads more, other people use their eyes more. This and other important data are used to give the lenses of the glasses an individual surface design.
ATTAINING THE PARAMETERS
The customer’s personal data linked to the frame are more important than ever. The more precisely the optician knows all of the parameters, the more exactly the glasses lens design can be optimised using the software. The necessary data are obtained using high tech cameras. They provide objective images of the person wearing the glasses with the desired frame. The software then measures all of the relevant centring data and stores this.
Expert advice in a personal discussion about the various options increases the visual comfort. Progressive lenses have never been this individual, because not every customer has the same needs and it is not the same parameters which are important for every person who wears glasses.