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HomemilensesGT2 3D Asiana: Innovation Based on Face Structure

GT2 3D Asiana: Innovation Based on Face Structure

Face shape is an important factor when it comes to designing progressive lenses. The underlying bone structure of the head and face is markedly different between Caucasian and Asian populations.

People with an Asian ancestry are the fastest growing ethnic group in Australia and New Zealand and the populations of which are heavily concentrated in the 20 to 44 years age group so the ratio of presbyopes is high1.

In the Australian Census 2006, 1,696,568 Australian residents declared they were of Asian ancestry – about 6.7 per cent of all responses. In Sydney (16.88 per cent) and Melbourne (16.18 per cent) the figure was much higher2.

In the 2006 New Zealand Census 9.2 per cent of people declared that they were of Asian ancestry3.

The structure and shape of the human face is an important factor when it comes to designing progressive lenses. The underlying bone structure of the head and face (craniometry) is distinctly different between Caucasian and Asian populations.

The cheek structure of the Asian face has a flatter profile while the bridge of the nose is less pronounced. The combination of these two factors has a substantial impact on the final position of wear of spectacles, particularly pantoscopic tilt and the bow angle. Subsequently, these factors need to be incorporated into progressive lens design to ensure best visual performance.

To meet the challenge of fitting people with an Asian shaped face with the right lenses Carl Zeiss Vision has made the GT2 3D Asiana available to the Australia and New Zealand market.

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Position of Wear

During 2007, Carl Zeiss Vision conducted position of wear studies in Shanghai, China. In this study, over 400 existing presbyopes were measured for all parameters relating to frame and lens position. These parameters were then compared to 250,000 measurements that had been gathered in Europe over a period of some ten years. The key differentiating factors were pantoscopic tilt and bow angle. These findings led the Carl Zeiss Vision lens design research team to develop an enhanced progressive lens design specifically for the position of wear for Asian facial structures, resulting in GT2 3D Asiana by Zeiss.

The position of wear is of critical importance to delivering correct power in distance and near, and ensuring good binocular vision. This becomes particularly relevant with higher prescriptions and prescriptions with oblique cylinder. Coincidently, many Asian spectacle lens wearers do have high prescriptions.

Lens alignment in progressive lenses relies on accurate specification of the ‘Positionof- Wear’ parameters. Position of wear is vitally important in progressive lenses as pantoscopic tilt introduces oblique astigmatism, which results in an increase in sphere power and unwanted cylinder power. These unwanted power changes can reduce the optical performance of a progressive lens, particularly through the central viewing zones.

The position of wear of the fitted lens needs to be modeled upon the most accurate data in order to apply the necessary optical corrections across the lens surface during the optical optimisation process. By using the most accurate position of wear parameters, wearers can therefore enjoy the best optical performance possible.

Based on the above information, the position of wear values for the new GT2 3D Asiana design is calculated to optimise for the average position of wear found amongst Asian spectacle wearers (Table 1). GT2 3D Asiana is based on these unique position of wear values inherent to the Asian facial structure. As with the European version, GT2 3D Asiana Progressive Lens is designed with particular emphasis on binocularity in order to deliver a more natural viewing experience.

‘Binocular’ Vision

Binocular vision with stereopsis, or the ability to perceive three-dimensional depth from two distinct retinal images, represents a highly evolved and incredibly sophisticated utilisation of sensory input in humans. Good binocular vision can significantly enhance our visual capabilities and performance compared to monocular vision by providing us with better spatial localisation and depth perception; improved visual acuity and contrast sensitivity; faster detection and recognition of objects; and a wider field of view4.

This enhanced visual performance also contributes to improved reaction time5, which is critical for tasks such as driving. Nevertheless, binocular vision performance is often taken for granted, although maximum visual comfort and performance can only be realised when the two eyes work together in perfect unison.

With the application of technologies such as horizontal symmetry (DE Patent 3016935), the binocular vision performance of Zeiss Progressive Lenses is maximized compared to conventional progressive lenses. Horizontal symmetry balances the optics of each lens design to either side of the progressive eye path in order to minimise differences in power, prism, and magnification between corresponding points across the right and left lenses.

Visual performance is fully optimised for every prescription due to the real-time fabrication of every GT2 3D Asiana. In fact, the binocular field of clear vision of GT2 3D Asiana is up to twice as wide compared to conventional progressive lenses.

Moreover, the average binocular difference in power between the right and left lenses of GT2 3D Asiana is up to 60 per cent lower compared to conventional progressive lenses.

Smaller Frames

Many of today’s presbyopes are choosing smaller, more fashionable frame styles that often compromise near vision utility with traditional progressive lens designs. In fact, according to industry estimates, small frame styles with vertical (or ‘B’) dimensions of 30 mm or less represent over 65 per cent of the frame styles introduced in recent years. Although the global geometry of the new GT2 3D has been carefully defined based upon ongoing vision research and an extensive database of fitting parameters from years of customised progressive lens production, many wearers will inevitably choose frame styles that necessitate a short corridor length and high near zone in order to attain sufficient near vision utility.

Fortunately, in order to meet the requirements of small frame performance while still delivering many of the optical benefits of this new progressive lens design to wearers, a ‘short-corridor’ version of GT2 3D Asiana is also available. With a corridor length that is approximately 3mm shorter, GT2 3D Asiana Short offers up to 75 per cent more near vision utility in small frame styles than the standard GT2 3D Asiana Lens design. Consequently, progressive lens wearers can enjoy the most important visual benefits of the new GT2 3D Asiana Lens design across a broad range of frame styles, down to a minimum fitting height of only 14mm.

For further information on GT2 3D Asiana contact Carl Zeiss Vision Customer Service on: (AUS) 1800 882 041 or (NZ) 0508 765 271 or your local Carl Zeiss Vision Territory Manager.


Mark Thyssen, Dip. Opt. Christiaan Huygens School of Precision Mechanics, Rotterdam, Netherlands. has practiced as Ophthalmic Optician and Optical Dispenser in Europe and Australia. He is currently employed as Director – Product Management, Carl Zeiss Vision Asia Pacific and has been employed by Carl Zeiss Vision (and previously SOLA Optical) for the past 20 years. He has held various positions in the optical industry over the past 30 years, from Sales Representative, Lens Detailer, Technical Marketing and Marketing and Sales management.

References:

  1. Australian Bureau of Statistics 1997, Migration Australia, 1999, cat. no. 3412.0, ABS, Canberra
  2. Australian Bureau of Statistics 2006 Census, based on the number of people who declared Asian ancestry
  3. Statistics New Zealand 2006 Census
  4. Jones, R. and Lee, D. “Why two eyes are better than one: the two views of binocular vision.” Journal of Experimental Psychology: Human Perception and Performance, 1981; Vol. 7, No. 1, pp 30-40.
  5. Justo, M., Bermudez, M., Perez, R., and Gonzalez, F. “Binocular interaction and performance of visual tasks.” Ophthalmic & Physiological Optics, 2004; Vol. 24, No. 2, pp 82-90.