# Thread: Why Does Zeiss's Near Zone Optimization Reverse the Axis?

1. ## Why Does Zeiss's Near Zone Optimization Reverse the Axis?

I had a patient who got a pair of digital eyeglasses from the SmartLife branch of Carl Zeiss based on my prescription. From my understanding, this is a more versatile progressive solution, and Zeiss officially measured the monocular pupillary distance (PD) and dimensions for lens fitting for the patient.

Initial prescription:
R: -4.50 -1.25 0° ADD: +0.5
L: -4.75 -1.00 175° ADD: +0.5

Zeiss optimized prescription:
R: -4.57 -1.21 2°
L: -4.81 -0.98 173°

However, what surprised me is the optimized prescription for the near zone by Zeiss:
R: -4.09 -0.97 173° ADD: +0.6
L: -4.36 -0.68 2° ADD: +0.6

I'm curious about how Zeiss designed the near zone to completely reverse the previously determined left and right axes for the other distance zones.

2. I would guess that the fact that the axis is "reversed" is just a coincidence, that's just how the digitally optimized Rx works. But I am curious to hear other's opinions. At Hoya and Essilor I have some people in their labs who gave me their direct numbers if I ever have a technical question like this. Call up your Zeiss lab and ask to speak to their expert, when the customer service person says what's the question and they can't answer it they will pass you on to someone who can.

3. Your axis from the two eyes is only 5 degrees apart.
It may seem like the axis was reversed, however, the compensation was done for the near area.
Near area compensation is done the same way, but separate. The center of rotation distance is different than the distance, the impact of pantoscopic tilt and wrap are different on near than distance, this is also why you see a difference in cylinder from distance to near.

4. Originally Posted by lensgrinder
Your axis from the two eyes is only 5 degrees apart.
It may seem like the axis was reversed, however, the compensation was done for the near area.
Near area compensation is done the same way, but separate. The center of rotation distance is different than the distance, the impact of pantoscopic tilt and wrap are different on near than distance, this is also why you see a difference in cylinder from distance to near.

Hi lensgrinder，

I have benefited greatly from your response. As an industry giant, Zeiss has unparalleled capabilities in technological innovation. However, as someone involved in end-user sales, I believe that the smartlife product line has deviated from its intended research design in terms of actual user experience. In many cases, users are not getting what Zeiss has designed. The customer feedback for the SL series is far more negative compared to other series. The reason for this is simple: the more complex a system is, the more prone it is to errors. The principle of Occam's razor applies to any field.

Here's my personal summary of the SL series:

1. This series requires very detailed testing data, such as individual pupil distance, individual pupil height, frame size, etc. However, there is a significant margin of error in the testing process. Even when using professional tools like the Zeiss VISUFIT 1000, slight variations in the positioning of the device during testing and minor differences in the software's marking of pupil positions can lead to significant variations in the final data. For example, when measuring both eyes of the same user, the pupil height data for the right and left eyes may differ by 2mm, and the tilt angle of the frame may change from 7° to 2° if the user adjusts their glasses slightly.

2. Even with the VISUFIT 1000 and other professional Zeiss tools like wavefront analysis and higher-order aberrations measurement, the data provided to the Zeiss center often consists only of the standard prescription along with individual pupil distance, individual pupil height, and frame size. In fact, to my knowledge, many stores do not have the VISUFIT 1000 and instead manually measure the user's pupils with a ruler, neglecting to measure the tilt angle.

3. Considering the situations described in points 1 and 2, one might wonder if slight testing errors or, rather, measurement discrepancies (as any measuring instrument has its own margin of error) might undermine the optimization of the SL series. Does it become counterproductive to further optimize it?

4. Additionally, there are some issues with Zeiss' user education and end-user training. For example, many of my colleagues in other stores complain that due to the 4mm disparity between Zeiss' processing center and the optical center, users often complain of blurriness with the SL series. Some opt to simply add 4mm to the measured pupil height. Zeiss training staff only provide a simple instruction: if the tilt angle is significantly less than 8°, they need to compensate for the pupil height by dividing the angle difference by 2. Consequently, the testing methods used in the market can vary greatly. I hope to receive an authoritative answer here. Should the data obtained through VISUFIT 1000 testing require no compensation and be submitted directly to Zeiss' processing center? And when stores conduct their own tests, should compensation be applied?

5. Zeiss has optimized its products for different ethnicities, but from my understanding, is it correct to say that the only difference in the Asian version is the inclusion of the tilt angle measurement? This factor also relates to the issue described in point 3. For example, if face shape design is based on big data, does it work effectively for everyone when choose SL single vision or digital?

Thank you a lot.

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