Last month, third year students visiting ABDO’s new National Resource Centre to sit their final practical exams saw a few changes to previous years. One of these was the inclusion of measurements for individualised progressive power lenses (PPLS) for the first time.
Some students were unprepared for the requirement to measure pantoscopic tilt and face-form angle. A few were used only to fully computerised measurement systems in work and claimed not to have access to manual tools. Others admitted to working in practices where the lenses that are described as ‘tailor-made’ are not truly personalised and are simply available in a variety of corridor lengths and had never taken the required measurements.
Here lies a problem. Even within the industry there is considerable confusion around terminology. Digital surfacing techniques, namely ‘freeform’ technology, refers only to the method for shaping the surface of the lens. Any lens design can be made using freeform surfacing, even lenses/surfaces that are traditionally either moulded or surfaced using conventional techniques. Freeform is not the same as personalised, though personalised lenses can only be manufactured using freeform technology.
There are many terms for personalised lenses – Zeiss keeps it simple with Progressive Individual, Rodenstock uses ILT (Individual Lens Technology), Hoya signify individual design by ID, BBGR by Mio, others are less obvious without knowing their range.
In short, an individualised design is one in which the prescription is compensated to take into account any parameters that do not fit with the standard default fitting characteristics that traditional PPLs require in order to perform effectively. Key measurements that are taken into account are pantoscopic angle and wrap angle, however, brands differ and most also require one or more additional measurements such as: working distance; optical centre distance and inset; vertex distance regardless of power; as well as frame depth and the ability to match corridor length or specify a different corridor length if appropriate. BBGR’s Intuitiv Plus Mio can even be adapted for right and left handedness.
It is over 20 years since manufacturers in Germany, first Rodenstock, then Zeiss, pioneered personalised PPLs utilising the latest freeform digital surfacing technology. In the UK these products got off to a slow start largely because optical assistants who did not understand them measured the extra tailor-made parameters incorrectly, and when they did not measure them at all manufacturers still accepted orders and used default parameters.
A personalised progressive manufactured using the standard default parameters of traditional PPLs will be little different in performance to a standard lens. If the patient’s add has increased, and the reading area narrowed, it may even be a little worse, or at least perceived to be worse relative to the extra price paid. Individualised progressives are fantastic for astigmats, people with narrow or wide PDs, frames that fit outside of standard parameters (8º to 12º pantoscopic tilt, 0º to 5º face form angle – consult your manufacturer for exact defaults) and patients with high prescriptions or prismatic correction.
The advent of relatively inexpensive digital measuring devices and simple to use manual gadgets means there is no excuse for not having the correct measurements, and the universal availability of freeform manufacturing technology means that now almost every manufacturer offers freeform surfaced lenses.
The ability to personalise progressive lenses to take account of individual differences from the standard default parameters is no longer the sole preserve of global multinational giants. For example, Optik Mizen asserts that the ‘exceptional’ performance of its Life Synchronicity PPL is equivalent to that of Nikon Seemax Master, Zeiss Individual and Essilor’s X Series, due to the combination of lateral dissemination technology, which takes into account the way insets vary depending on overall PD and working distance and Opus Curve Optimised Dual Surfacing.
High tech postural tracking helped Essilor develop its Varilux X series
Dual surfacing is an important differentiator between true personalised lenses and those that are surfaced only on the back surface incorporating the progression and the cylinder onto a puck with a spherical front surface. These designs may be freeform, however they are sometimes less satisfactory than traditional style PPLs. When putting the entire progression on the back of the lens the requirements of ‘best form’ means in order to avoid a convex back surface the base curve of the lens must be very much steeper than would ordinarily be the case and some patients are unhappy with the increased thickness of these lenses that are often sold as an opticians’ own brand.
This specific issue, and more besides, has been solved by the Optician Awards 2018 Lens Product of the Year – ARC Steady from Caledonian Optical. This utilises Camber technology, where an increasing cylindrical element is moulded into the front surface of the semi-finished blank, and complex algorithms are used to calculate the freeform rear surface of the lens. This seems to satisfy the need of patients for best form vision while simultaneously reducing the need for multiple adds and base curves in semi-finished form and offering a competitive price point relative to the visual quality achieved.
Camber technology, pioneered by Younger Optics, is also available from Norville, Lenstec and more than 30 other independent laboratories who offer a point of differentiation for independent opticians when compared to the larger groups. Many independent labs also offer their own fully personalised lenses. For example Jai Kudo’s Wideview Confidence individually tailored freeform progressive lenses claim the ultimate in truly personalised optics using Digital Ray-Path technology taking into account the patient’s prescription, lifestyle and measurements such as BVD, pantoscopic tilt and dihedral angle with minimum fitting depths from 14 to 25mm across the range.
The big guns
As independent labs have caught up the global players have not stood still, launching improved versions of their personalised lenses as well as offering new user friendly and cost-effective measuring systems based on tablet computers and desktop mirrors. Essilor’s Varilux X-Series has been improved by the provision of new X-Tract technology which uses an iPad to track the wearer’s eye and head movements during common near vision tasks.
Zeiss Individual 2 as well as allowing for pantoscopic angles from -10º to +30º and seven corridor lengths tailored to frame fit offers further personalisation for balanced, near and intermediate visual preferences: Balanced, as the name suggests is for patients who prefer a high-quality universal viewing solution and regularly alternate between all visual ranges; Near is for people who work frequently in the close visual range (30 to 60cm) doing mainly static visual tasks (eg reading, handicrafts) and prolonged indoor activities requiring excellent near vision; Intermediate is for those that often work in 60 to 90cm range (eg computer work) and engage in dynamic visual tasks requiring frequent changes in visual range such as driving and sport.
Sport is an area where tailor-made progressives come into their own, catering for the significantly increased face-form angles associated with wrap-around sports frames as well as balancing the lens towards dynamic distance vision while retaining the ability to mark a golf card, read one’s watch or use phone based GPS systems and other sports gadgets. Shamir is probably market leader in this area, supplying brands such as Adidas with its Rx lenses, and catering for the widest range of sports frame parameters with their Autograph Attitude III lenses. Just when you thought there could not be any more terms for face-form angle (on top of wrap, bow, dihedral angle, etc), Shamir has added another term – panoramic angle – and cater for values from 0º to 40º across their range. With base curves available up to +10.00D varifocals are now an option for almost any frame.
Base curve is a key reason why manufacturers of frames have recently entered the tailor-made progressive market. Most opticians have made the mistake of ordering a standard lens in a low minus power and flat base curve to a frame that is too wrapped. The consequence of this is that the frame front is less bowed than it should be and the sides splay out, often in a way that cannot be adjusted. The Ray-Ban Wayfarer classically suffers from this problem and helps explain why Ray-Ban now offers its own prescription lenses.
Unfortunately, Luxottica, despite an alomost complete merger with the world’s largest producer of varifocals, and the Ray-Ban brand appealing to all ages, seem only to offer single vision options at present. Silhouette on the other hand, whose rimless mounts typically have a +5.00D base curve on dummy lenses, have introduced its Vision Sensation progressives to solve this problem.
Base curve optimisation used in Silhouette’s Vision Sensation lenses
The claims for Optik Mizen’s lenses are based on ‘published marketing data and “Rotlex” mapping comparisons, augmented by patient trials/feedback’. Iso-cylinder plots no longer seem to be available to opticians and this makes it difficult to accurately compare lenses.
Can opticians take their suppliers’ word for it when they claim one lens is better than another?
The simple answer to this is yes. Rodenstock claims that Impression FreeSign 3 is its best progressive lens yet, but how it compares to other personalised lenses is a matter of design philosophy and wearer preference. However, you can be sure that true bespoke, personalised, individualised tailor-made lenses, measured correctly, are better than non-personalised freeform lenses (that sometimes claim to be personalised because they offer a range of corridor lengths).
If your patient wants a frame that fits flat, or steep, or is wrapped more than 5º, then personalised PPLs are the only option if non-tolerance is to be avoided. For patients with any significant astigmatism, a narrow or wide PD, or inset/working distance that differs from the average, individually tailored varifocals can make a significant difference to their quality of vision.
If individualised lenses have largely been ignored by the professions for 20 years, it is staggering also that the world’s thinnest plastic lenses have also been largely ignored since they launched in 2006. Now Tokai UK combine its 1.76 bi-aspheric technology with its state of the art individualised progressive NeuroG. With 50 available insets alone this offers a new level of customisation, and if you think 1.76 will be no thinner than 1.74, try them, you will be amazed.
Once upon a time opticians used to tell patients that they would experience ‘distortion’ with their varifocals to either side of the reading area, that the swim and sway in their vision was normal, and that anyway there was always the non-tolerance guarantee if it all went horribly wrong. Then a bright spark coined the phrase ‘areas of soft focus’, a concept before its time, to describe the aberrational astigmatism.
The thing is this somewhat exaggerated claim for conventional progressives has now come into its own with personalised lenses. In this author’s experience, having tried almost all the lenses above, and many more standard progressives besides, soft focus to the side is exactly right – there is no distortion in sight.
The General Optical Council, in Standard of Practice 3.1 expects opticians, as part of obtaining valid consent, to inform the patient of their ‘options in terms of examination, treatment, sale or supply of optical appliances’. Now every manufacturer offers personalised lenses that offer so much visual benefit to many patients it is surely time for opticians to catch up with this 20-year-old technology and offer patients the state of the art varifocals they deserve. It is the patient’s choice to say no.
