Multifocal designs have evolved dramatically over the years, and we want to introduce some of the terminology and
latest developments to you.
As you may have heard from media advertising, the buzz words are: HD, Digitally Enhanced, Free Form and IScription. All of these have been around for the last few years and as the older generation designs are gradually
discontinued, these lenses have become the designs of choice.
Multifocal lenses are used to correct presbyopia and other disorders of accommodation. The lens has the wearer’s
distance prescription at the top of the lens, intermediate prescription in the middle and the reading power at the
bottom of the lens. The power gradually changes from the top to the bottom of the lens providing providing vision
for all distances. The length of the progressive power depends on the design of the lens. All multifocal lenses have
some level of peripheral distortion, again dependent on the design.
Older generation lenses were relatively unfriendly designs as the design and pattern of the lens were
Traditional lens manufacturing involved using a semi-finished lens blank. The multifocal design, front curve of
the lens and difference in power from the top of the lens to the bottom (the add power) were moulded on the front
surface of the lens. The laboratory would then grind the prescription into the back surface of the blank using a
generator. The lens would then be polished to complete the process. This process did not allow for any
customization of the progressive designs.
Free-form manufacturing (also referred to as Digital or HD lenses) can produce a highly customized and highly accurate finished lens. While with traditional lenses the semi-finished front pattern was set with “Freeform, HD or Digitally Enhanced” lenses the designs are tailored to each prescription.
This is possible to due to the modern software and manufacturing processes which allow the input of individual
prescriptions and eye centration details, and some designs even take into account the position of wear of the frame
to create a truly customized lens that is not possible with older generation lenses.
This complex manufacturing of a multifocal lens is done on computer-controlled machinery allowing ‘freeform
surfacing’, as opposed to the earlier process, thus explaining the difference in price. In short, the price is based on
the technology used and the year the lens is launched.
These modern multifocal lenses result in higher definition, comfortable transition between the top and bottom of the
lens and wider corridors. These enhancements result in quicker adaptation, with easier, more natural postural
behaviour. Added to this special design options are available to further accommodate your specific visual demands.
We, at Vision, have always believed in providing the best optical/visual solutions to our clients and introduce the
latest technology as soon as it gets launched.
“I-Scription” lenses by Zeiss are a further subdivision of “High Definition” lenses.
Lenses are normally prescribed in quarter dioptre steps i.e. 0.25, 0.50 etc. With I-Scription lenses your lenses will
be custom made in 0.01 steps introducing a new level of customisation and accuracy. That is quite’ wow’ in terms
of improved night vision, colour vision and contrast. In general these lenses usually work very well with people with
complex prescriptions or those people who always seem to not see crisply even with an updated prescription. At
Vision optometrists we have all the equipment necessary for prescribing these unique lenses.
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