I have been asked about free form ophthalmic lens designs, sometimes called digital surfacing, what are they and what is different about them versus regular lenses? I am not at all technical and will approach this subject more of a user perspective and my own knowledge from working for lens companies.
Photo by Seiko
Free form lens technology is not that new but bringing it to the market on an individual lens prescription basis is relatively new. Progressive lens manufacturers have used free form technology for years to design and manufacture the molds that progressive lens blanks are then cast from. Then these lens blanks are ground and polished into the finished prescription. Each process has margin for error so in theory cutting down the number of processes makes for a more accurate prescription. Advances in computer technology have made it possible to do this.
The technology is Computer Numerically Controlled (CNC) machinery. The CNC machine makes thousands of cuts in all the different planes on the back surface of a single vision spherical lens to a very high degree of accuracy for a specific ophthalmic prescription. The lens is made for the individual patient and the specific frame. The computer program will calculate the optical performance of thousands of locations covering the progressive lens surface, taking into account many parameters including the following:
- Lens prescription
- Pupil distance
- Lens index of refraction
- Lens center thickness
- Distance from the eye to the back vertex of the lens
- Distance from the lens to the object
- Pantoscopic tilt of the frame
However, the specific progressive lens design that the machine is programmed to follow is still a key variable so although there is less margin for error in the actual lens production the design, the correct prescription and fitting are still just as important.
I personally prefer the free form lenses as I think the performance is better and would not go back to traditional progressives. I recommend that if you haven’t tried them to do so. My particular personal favorite is Izon by Ophthonix. Most of the major lens companies have free form lenses. Here are some but not all of the companies that proved them Shamir, Essilor, Signet Armorlite, Zeiss, Seiko and ODC.
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