Over the past 40 years, the pace of technological advancements has accelerated at an unprecedented rate. This rapid progression can be largely attributed to the exponential growth in computing power, which has enabled the development of increasingly sophisticated and powerful technologies.
The internet revolution has fundamentally altered how we communicate, access information, and conduct business. Additionally, the rise of artificial intelligence and machine learning has opened new frontiers in automation and data analysis, reshaping healthcare. Over the same period there have been many changes in ophthalmic optics and the lens landscape including materials, coatings, lens designs, and lens treatments. But the biggest changes have been brought about by changes in technology. Digital devices have driven the requirements for different lens solutions and digital lens production, so-called freeform lens production, has allowed for these products to be improved upon and made new designs possible.
THE RISE OF COMPUTERS
By the early 1990s the use of computers, driven by easy-to-use software, started to become widespread in both homes and offices, driving the need for different visual solutions than provided by the single vision and multifocal lenses available at the time.
What was needed was a lens with computer distance at pupil height and additional reading power inferiorly.
Also in the 1990s, the first widely used enhanced reader, Access, was produced by Sola. The digressive design, ordered with near script, was available in two digressions of 0.75D and 1.25D. As such it could be used on computer screens.
In the article ‘Making the mold and breaking the mold – the rise and fall and rise of sola optical’ Andy Griffiths stated, “I am not really sure if we intended to market it for desk use, but it soon became apparent that Access would be most useful for workers who used a VDU (visual display unit)…”.1 Now most lens producers have specific designs for using with desktop and laptop computers, and these designs form a vital part of a practitioner’s portfolio in combating ergonomic and vision problems for computer users.
THE RISE OF SMART PHONES
The first smart phone was introduced in 1994 with the IBM Simon, and smart phone and tablet usage became common in the mid-2000s. At the same time, Essilor brought out the first ‘anti-fatigue’ type lens, providing a small amount of additional power in the lower part of the lens, which helped reduce eye strain. Most lens producers followed suit with lenses aimed at teenagers to prepresbyopes who experienced asthenopia with prolonged close tasks. Initially these lenses were produced with low boost values of 0.40D to 0.80D, specifically for teens and people in their early 20s, but the profession requested constantly higher boosts so they could dispense to early presbyopes.
EXPANDING OPTIONS
Traditional grind methods could be used to produce both of these types of lenses as the design and digression, or boost was moulded onto the front surface. However, there were limits in that the number of different boost powers and digressions was dictated by the number of lens blanks a manufacturer could reasonably keep in stock. Ranges and designs were opened by the advent of freeform manufacturing, which was introduced in the early 2000s. Freeform technology, also known as digital surfacing, allowed for design, addition and/or digression, and corridor length to be ground on the back surface of a spherical lens blank, reducing the number of blanks needing to be stocked.
The first common claim that lens manufacturers made with respect to digital surfacing was that by putting the design on the back surface – that is, closer to the eye – the keyhole effect was reduced, making the corridor appear wider. In reality, freeform manufacturing does so much more, allowing for the creation of customised, high-precision lenses by using computercontrolled machinery to sculpt the lens surface with extreme accuracy. The ability to change the curvature at every vision point on a lens allows for optimisation to reduce the base curve effect and reduce aberrations, such as oblique astigmatism, spherical aberration, and distortion. This makes progressive and digressive lenses much easier for patients to wear by reducing swim. The ability to move the aberration Minkwitz astigmatism around the lens, into areas less noticeable to the patient, allows for better use of the full corridor width, making intermediate and near areas appear wider.
As any lens design can now be produced on the back of a simple spherical base curve, digressive lens designs have expanded to give extended readers: lenses that provide an additional 20–30 cm of reading distance, desktop computer lenses that allow for ergonomical seating or standing positions, and so-called indoor progressive lenses that allow for clear vision from 40 cm out to up to 4 m. These designs give practitioners perfect solutions for any visual task and a clear route for multiple spectacle solutions. Gone are the days of making one design of lens perform for every visual task.
Freeform lens production would not, at first glance, appear to offer much to improve antifatigue type lenses as usually there are only two or three boost powers. However, now vision through these lenses can be much improved by taking into account compensations for eye rotation due to Listings Law for both distance and near, along with correction for effective near astigmatism. Depending on pupillary distance (PD), the act of converging to 40 cm in downwards gaze can alter the cylinder axis by as much as five degrees. Effective near astigmatism, caused by the angle of incident light, is greater for the low boost powers of antifatigue lenses. These compensations can make significant improvements to vision.
In addition to this, the advent of wavefront aberrometry, which produces a detailed map of both lower and higher order aberrations (HOAs), and the use of digital surfacing, allows the production of lenses that take into account the individual’s wavefront profile. This leads to sharper, clearer vision with better contrast and reduced glare. Vision for night driving can be significantly improved with compensations for HOAs.
THE RISE OF ARTIFICIAL INTELLIGENCE
The way a lens is calculated is the other major breakthrough that has occurred recently. Until 2018, and the launch of Rodenstock’s DNEye Pro, all spectacle lenses were calculated using a vertex sphere and the rotation of a standard reduced eye which, depending on the model, was emmetropic and had a length of 24 mm and a spherical cornea.
Using the measurements provided by the DNEye scanner 2 – pachymetry, topography, aberrometry, and pupil mapping – a model of the patient’s individual eye can be created and used to calculate each vision point on a lens. Using the old method of calculation, each lens design worked perfectly only for a patient who had the equivalent of a standard reduced eye; essentially only about 2% of the population. Lenses produced using the patient’s eye for calculation perform as they should for most patients, minimising swim and allowing the widest use of the available corridor.
Leading on from this, using artificial intelligence (AI) to analyse over half a million DNEye scans, an approximate eye model can be extrapolated from the patient’s scripts and PDs.
MEASUREMENTS AND FITTING
With all the optimisation and compensations allowed for with freeform lens production, it stands to reason that modern lenses need to be fitted accurately. Since the turn of the century, numerous measuring devices have been introduced to aid dispensers in the measuring of lenses. Initially, towers using a jig to show the position of a frame, or using a two-camera system and trigonometry were available. Later, tablets – again using jigs – were developed as smaller and more convenient measuring devices.
These devices cannot replace an experienced dispenser. They are simply tools to enhance accuracy and give repeatability of measurements. Mostly, they simply take a photograph of the patient wearing the frame and require detailed analysis of that picture.
The skill is in observing the patient’s normal posture and then ensuring their stance while the picture is being taken. Often, manufacturers are told that the instruments are not exact and require calibration, but it must be considered that if a patient who generally slouches, stands up straight for the picture it will affect the pantoscopic tilt of the frame. A difference of two degrees will produce a discrepancy of 1 mm on pupil height. Posture in the form of patient set up is vital. Another important aspect of measurement is the correct fitting of the frame before measurements are taken. Again, a skilled dispenser can make a significant difference to the patient’s final experience with their new spectacles.
THE FUTURE
While the past 40 years have seen significant breakthroughs in spectacle lens design and production, the future holds unlimited potential. Digital printing offers possibilities for both lens and frame production. The use of biometry in customising lenses for the individual eye could revolutionise the design and production of myopia control lenses to accurately control the amount of peripheral defocus. When we consider that most of the visual function takes place in the visual cortex, not the eye, current and future research will make for more interesting changes.
Nicola Peaper BSc (Hons) Ophthalmic Optics, Cert 4 TAE, qualified as an optometrist in the United Kingdom in 1985 and practised in private and corporate practice in there for 20 years. In 2001–02 she was employed as ophthalmic advisor to Kensington, Chelsea, and Westminster Health Authority.
After moving to Australia in 2005, she worked in fitting laboratories advising on procedures and quality. In roles as state and national training manager, she gained extensive experience in presenting the technology behind, and the prescribing and fitting of, ophthalmic lenses.
Nicola Peaper recently retired from her role as Professional Services Manager for Rodenstock Australia.
Reference
- Griffiths A in Sothman B. Making the mold and breaking the mold: The rise and fall and rise of Sola Optical, available at solahistory.com/chapter-4-02.html [accessed July 2024].
