BETTER VISION: Mr Gahr, what makes individualized eyeglass lenses different than regular ones?
Well, obviously even conventional eyeglass lenses are to some extent tailored to the wearer. That's because you are basically following a prescription, in other words getting the right lens power in the right position in the selected frame to provide the wearer with better vision. If another wearer were to put on my glasses, it's unlikely they would have optimum vision. When we refer to individually "optimized" lenses we're really talking about taking into account other relevant, personal information about the wearer within the optical design by calculating the ideal lens surfaces for their needs.
As a rule, the eye care professional will perform a refraction and write the lens prescription.
What lenses are required?
The next step is for the wearer to choose a frame. But that's really as far as the conventional approach goes. Of course an eye care professional prescribing off-the-shelf lenses will measure the visual point of both eyes positioned within the selected frame in order to ensure correct glazing of the lenses that he or she subsequently orders from a company like ZEISS. But the ultimate position of the lenses in front of the wearer's eyes – which is determined by the specific frame style chosen – will not have been taken into consideration when calculating the lenses.
BETTER VISION: So the biggest difference with individually optimized lenses is how they are tailored to the frame...?
Volker Gahr: That's certainly a crucial difference, though it's not the only one. The more ZEISS understands how an eyeglass wearer looks through their lenses with the selected frame, the more accurately the lenses can be crafted so that the wearer ends up looking through them in the most natural and optimum way possible. This means that they end up with a perfect optical vision aid that has been tailored precisely to their individual needs. But to achieve this, the eye care professional needs to determine other important personal parameters in addition to the point at which the wearer focuses when they look straight through the lens – and those parameters need to be accurate to a tenth of a millimeter!
For example, what distance do their eyes tend to be from a book or computer screen? At exactly what height do they look through the lens in the frame they've chosen? How does the inclination of the frame affect the wearer's vision? That's something that depends not only on the frame but also on the shape of a person's face. What's the back vertex distance, i.e. the distance between the back surface of the lens and the front of the cornea? What's the curvature of the frame? Precise measurements need to be made of the frame dimensions and the height and width of the lens.
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