Taking a Farsighted Approach to Myopia

Alarmingly, around 90 per cent of university age individuals are developing myopia in some regions in Asia.¹ In the western world the incidence and progression of myopia is also increasing at pace.

Understandably, there is great interest in myopia prevention strategies.

There’s also plenty of interest in controlling myopia and slowing its progression. Most myopia control strategies centre on contact lenses and pharmaceutical control. Spectacle lenses, such as progressives, bifocals, occupational and digital designs, also have their place, reducing accommodative-convergence demand. Then there are optics specifically designed to slow the progression of myopia.

Dr. Saulius Varnas, Principal Scientist and a lens development and technology specialist with the Zeiss Vision Care Business Group says Zeiss offers a couple of products to control myopia progression in children and juveniles in Australia and New Zealand. “MyoVision is a specialty single vision product with peripheral vision management that has been shown to slow down progression of myopia by 30 per cent over 12 months, in randomly selected six to 12-year old children with parental myopia.² A Synchrony MC progressive lens aims to reduce accommodative lag during near vision. Clinical trials demonstrated
myopia progression retardation of 25 per cent over 18 months and 21 per cent over two years respectively.”^3,4

Past and Present

In years gone by, people living with myopia did not have a lot of choice in terms of spectacle lenses.
Those with high levels of myopia suffered from a myriad of issues associated with what were usually very thick, heavy and potentially dangerous crown glass spectacle lenses often referred to as ‘Coke bottle’ lenses.

There were functional and visual issues too. Although high refractive index spectacle lenses have been around for many years they were, in the early days, rather heavy and brittle. They also suffered from nasty internal reflections and poor Abbe numbers, with patients often complaining of coloured fringes from chromatic aberration.

The first decent high refractive index plastic spectacle lenses were developed in the mid–1990s. One of the breakthroughs at this time was the 1.6 refractive index Hoya EYAS lens material. We noted excellent adaptation and cosmetic results. Patients too were very positive.

Anti-reflection coatings were also hitting their straps. This allowed for decent coatings that almost eliminated the surface and internal reflections that were often referred to as ‘power rings’.

Today we are spoilt for choice with some superb materials and designs.

Today we are spoilt for choice with some superb materials and designs

Obtaining Best Results

Frame selection is a critical aspect in obtaining excellent results: The laws of physical optics mean that no matter how high the refractive index, a –15.00D spectacle lens is always going to have significant edge thickness. Simply put, the bigger the spectacle frame and lens diameter, the thicker the edge.

These days a plastic 1.74 index aspheric lens design – in a small eye size and shallow frame – can provide superb cosmetic and optical results. We can observe, for example, a –13.00D lens in an optimum frame that many would guess to be more like –8.00D.

There are arguments for and against aspheric designs but on the whole they are well tolerated. Nowadays, a patient will rarely complain about coloured fringes and ‘things swimming around’, when they collect their new glasses.

Sometimes a change in design throws them off balance and switching from an aspheric design back to a standard design will resolve the problems and vice versa.

Explain and Demonstrate Options

When consulting patients with myopia, it is important to take the time and trouble to explain the reasons for the recommended frame and lens. Use simulators and examples to show the difference in edge thickness from a low index to a high index material, as well as the enhanced cosmetic appearance of an antireflective multicoat or aspheric design.

Most plastic (resin) spectacle lenses have pretty good impact resistance, compared to the riskier glass lenses. Although a 1.8 or 1.9 index glass lens does have its place, safety hardening should be considered. There are also blended lenticular lens designs that can make a difference for extreme prescriptions.

A lens meter or other instrument that can measure UV and visible light transmission can be handy for patient demonstration purposes, although most plastic spectacle lenses have very high levels of UV absorption. The majority of people are very much aware of looking good and will happily spend a small fortune on items such as make-up, hair products, cosmetic procedures, clothes and shoes. Demonstrating the various spectacle options helps convince spectacle wearers of the cosmetic benefit and everyone wins.

Lens for Myopia

Hastings

The major concerns of moderate to high myopes are mostly related to cosmesis, clarity and restricted frame choices. Conventional lens corrections are disadvantaged by thicker and heavier lenses, increased oblique astigmatism and, for high index lenses, the greater dispersion caused by their lower Abbe number. This leads to loss of visual clarity and consumer annoyance.

Hasting Optical Supplies has sophisticated solutions to minimise these lens issues and provide patients with a choice of larger and more curved frames.

Using freeform production and digital ray path optimisation technology the oblique astigmatism of high minus lenses is dramatically reduced.

Lenticular lens processing enhances the cosmetic appearance by reducing edge thickness and weight. It also allows the use of a lower index material without greatly affecting the cosmesis. Two lenticularisation methods can be ordered: ‘smooth lenticular’ with a user-defined optical region, or ‘lenticular frame shape’.
By combining Hastings Optical Supplies’ digital ray path technology and lenticular lens processing, a thinner, lighter and more comfortable lens with enhanced visual clarity is achieved.

References
1. www.nature.com/news/the-myopia-boom-1.17120
2. Sankaridurg, P., Donovan, L., Varnas, S., Ho., A., Chen, X., Martinez, A., Fisher, S., Lin, Z., Smith III, E.L., Ge, J. & Holden, B.A. (2010). Spectacle Lenses Designed to Reduce Progression of Myopia: 12-Month Results, Optom. Vis. Sci., 87(9), pp. 631 – 641.
3. Hasebe, S., Ohtsuki, H., Nonaka, T., Nakatsuka, C., Miyata, M., Hamasaki, I., Kimura, S. (2008). Effect of progressive addition lenses on myopia progression in Japanese children: a prospective, randomized, double-masked, cross over trial. Invest. Ophthalmol. Vis. Sci., 49(7), 2781 – 2789.
4. Yang, Z., Lan, W., Ge, J., Liu, W., Chen, X., Chen, L., Yu, M. (2009). The effectiveness of progressive addition lenses on the progression of myopia in Chinese children. Ophthalmic Physiol. Opt., 29(1), 41 – 48.