We have recently made some innovative changes to our lens calculation programs regarding freeform progressive and single vision lenses that we term variable decentration.

As standard practice all our progressive lenses (conventional and freeform) are pre-decentred as can be see in our Lens Manual. This means that thinner more cosmetically acceptable lenses can be produced as some of the decentration is already incorporated into the blank, meaning that we can work smaller thinner lenses to achieve correct centration.

However, for example, if a patient has a relatively wide pupillary distance and requires decentration that is less than the pre-decentred amount on the blank, this can cause some lenses to be thicker than needs be as we have to try and ‘cancel’ some of this pre-decentration.

On freeform products designed to shape we have introduced variable decentration. With this technology we have the opportunity to make the geometrical centre of the blank and the frame box centre coincide. Essentially we are moving the design within the lens rather than making a larger and thicker blank. This will produce lenses with more ‘balanced’ substances at nasal/temporal and top/bottom.

The variable decentration will also allow us to glaze frames that previously were too large, where the blanks available are not large enough when centres and heights are taken into account. By moving the design within the available blank we may be able to achieve the centres required when previously we could not.

Single vision freeform lenses may also be decentred within the lens therefore the optical centre will not necessarily be positioned at the geometric centre.

Email