Understanding Vision

No face is perfectly symmetrical, and no two people's eyes are the same distance apart

Only after the glasses frames have been precisely adjusted to the individual wearer can the lenses perform to their full potential.

16 March 2021

As children we discovered that the two sides of our faces are not same, i.e. they are not symmetrical. If you hold a mirror up vertically over the bridge of your nose and look at a mirror image of each of the two sides of your face, you can see how your face would look if it were symmetrical and how strange that would look. This will also show you how differently we see with our right and left eyes through our glasses. Thus, when the eye care professional adjusts eyeglass lenses to their frames, it is very important for him to know how you look through your glasses. Only then can the lenses be ground properly for the particular frames.

  • Only after the glasses frames have been precisely adjusted to the individual wearer can the lenses perform to their full potential.

    Only after the spectacle frames have been precisely adjusted to the individual wearer can spectacle lenses perform to their full potential.

Did you know that the even the best precision eyeglass lenses cannot perform to their highest potential if the centration, i.e. the adjustment of the lenses to the particular frames, the distance between your pupils, the proportions of your face and even your posture has not been measured properly? Up to 40% of valuable visual acuity can be lost this way. This is important for single vision lenses and especially important for the centration of progressive lenses. For progressive lenses all three vision zones (distance, intermediate and near) have to be optimally adjusted. Ideally, with a normal posture, the wearer should be able to read comfortably while looking through the near zone, work at a computer through the intermediate zone and drive a car with the distance zone. The correct centration and, of course, the selected lens design plays a decisive role in determining the spontaneous tolerability of progressive lenses. A difference of a millimetre can be crucial.

  • Analysis of the left eye and frame tracing

    Analysis of the left eye and frame tracing

In the past, eye care professionals did the measurements for the centration of spectacle lenses manually. The glasses wearer looked through the selected frames and the eye care professional used a felt pen on the spectacle lenses to mark where the pupils were and the distance between them.

Today, eye care professionals can work much more precisely – with an accuracy of a tenth of a millimetre. The i.Terminal®2 from ZEISS provides an objective image of the glasses wearer with the frames. With the selected frames, the customer stands in front of the centration device and centration is done with a high-quality photo, simply, quickly and extremely precisely. The benefit of this is that the adjustment procedure is more pleasant for you, since the eye care professional does not have to enter your personal space to do the measurement. You should stand as naturally as possible, and look through the glasses exactly as you would do in everyday life. The more precisely your eye care professional knows how you look through your new glasses, the better he or she is able to adjust the lenses. The i.Terminal®2 works with a high-tech camera and intelligent ZEISS software that with one click measures the centration data, saves it and makes the calculations for the production of the eyeglass lenses.

Our tip:

After the initial phase of getting accustomed to your new glasses, if you do not feel comfortable with them, the centration may not has been properly adjusted for you. Please speak with your eye care professional about this.

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