WE ARE LIVING BETTER AND FOR LONGER

We gain an extra three months life expectancy every year [1], around 6 hours per day.... one in every two little girls born today in France will reach the age of one hundred. Progress in the health field [2], although unequally distributed throughout the regions of the world, means overall that we are living better and for longer. But what about ocular health?

ls the human eye prepared for working in good health for over 100 years?

THE PREVENTION OF EYE DISEASES IS A MAJOR PUBLIC HEAL CHALLENGE

With the increase in life expectancy, some eye diseases and afflictions such as cataract or age-related macular degeneration (AMD) are unquestionably rapidly on the increase. Today the number of people affected by cataract is estimated at 250 million worldwide, with 100 million suffering from AMD, and these figures are set to double over the next 30 years Fig. 1 Within this context, the importance of preventing eye diseases becomes clear and the main objective is to minimise the risk of diseases occurring by taking direct action on the causes. (Fig. 1)

Fig. 1: An extrapolation of the prevalence of cataract and AMD (known epidemiological studies carried out in developed countries) in world population (UN World Population Prospects, 2013-2050). This projection does not take into account any progress that may be made in the health field, prevention or therapy, or genetic, environmental or other differences between the various regions. (Source: Simplified Extrapolation model, Essilor International, DMS, EL, Jan. 2013).

UV AND HARMFUL BLUE LIGHT ARE INVOLVED, AMONGST OTHER CAUSES, IN THE APPEARANCE OF CATARACT AND AMD

Age, tobacco smoking, diet and environmental factors such as prolonged exposure to ultraviolet rays are extensively noted in scientific literature as being risk factors in the occurrence of senile cataract.

ln addition to UV, visible light cana Iso have a cumulative impact on ocular health and particularly play a part in the development of AMD. ln fact, in addition to age, genetic factors or tobacco smoking, several epidemiological studies, including the "Beaver Dam Eye Study" and the "Chesapeake Bay Study" conclude th at the risk of AMD is greater in case of cumulative exposure to visible blue light [3].

And yet, within blue light, which is in wavelengths of between 380 and 500 nanometres (nm), it is important to distinguish the BAD blue from the GOOD blue [4]. The combined work of the Essilor International and the Vision lnstitute recently resulted in definition of the precise spectrum of retinal phototoxicity [5] and concluded that it is Blue-violet light, which is the closest to UV and centred at 435nm, which is the most harmful for the retina. This ,bad blue" can be of solar or artificial origin. Several independent studies undertaken by health agencies are now looking at the risks linked to new sources of artificial light, such as electroluminescent diodes or LED [6], because the latter have an emission peak situated in the „bad blue“ range (Fig. 2).

Fig. 2: Emission spectrums of various light sources.

On the other hand, Blue-Turquoise light, at wavelengths of between 465 and 495 nanometres (nm) is known as the „good blue“ because it acts on many non-visual functions that are essential for the body to function well [7].

Research programmes aimed at discovering new solutions to prevent or treat AMD must take account of this distinction between good and bad blue and attack harmful rays in a selective manner.

SELECTIVE PHOTO-PROTECTION USING INTERFERENTIAL FILTERS 

Various products offer protection against Blue-Violet light, such as therapeutic filters and sun lenses. Although the protection level is high, their colour can be an obstacle to permanent everyday wear (distortion of colours, appearance, vision in low indoor light) and also they necessarily cut out both bad and good blue light, making no selection between the two.

In order to offer selective photo-protection and a high degree of visual comfort for everyday wear, the use of interferential filter technology would seem to be the ideal solution for a clear lens. It cuts out the Blue-Violet light that is harmful for the retina, whilst maintaining optimal transmission of the Blue-Turquoise light in the neighbouring spectral band.

Twenty years of expertise in anti-reflective treatments and two years of research have enabled Essilor to achieve the design of the Crizal^® Prevencia^® lens, an interferential filter that reflects light in order to:

1. Filter out harmful rays, the Blue-Violet that contributes to AMD as well as uV rays which play a part in the appearance of cataract

The various anti-reflective coatings on both sides of the Crizal^® Prevencia^® lens filter out harmful light selectively:

- 20% of Blue-Violet light, [400-450 nm], is cut out thanks to optimised reflection of these wavelengths on the front side. The residual colour of the reflection proves its efficiency in the Blue-Violet range.

- On the back side, the interferential layers have been created to minimise the reflection of UV rays into the eye. This unique combination today offers the most complete eye protection available in a clear lens.

2. Allow beneficial blue light to pass through Crizal^® Prevencia^® transmits 96% of Blue-Turquoise light, [465-495 nm], thus preserving visual functions as well as some non-visual functions such as:

• stimulation of the pupil reflex, the retina‘s natural protection against over-exposure to light, centred at 480 nm,

• synchronisation of the biological clock (waking/sleep cycles, hormonal cycles, memory, cognitive performance, etc.) centred on a 30 nm bandwidth, [465-495 nm].

3. Whilst guaranteeing excellent lens transparency Crizal^® Prevencia^® ensures optimal vision clarity with overall visual transmission of 98%. This lens also retains the benefits offered by former generations of the Crizal range: the most efficient dirt-resistance on the market as well as excellent resistance to scratching, dust and water. (Fig.3)

Fig. 3: Illustration of the protection offered by the Crizal Prevencia lens on both the front and back (Plano Lens, 2 mm centre thickness, material Ormil, refraction index 1.6).

CRIZAL^® PREVENCIA^®, EFFICIENCY PROVEN IN VITRO

Essilor and the Vision Institute carried out an experiment on the retinal pigmentary epithelium (RPE) cells involved in the macular degeneration process, in order to model the protection offered by the Crizal^® Prevencia^® lens.

These retinal cells were photosensitized and exposed for 18 hours to narrow 10 nm bands of illumination in the blue light spectrum range between 400 nm and 500 nm, in the physiological conditions of sunlight on the retina. Photobiological work showed an average reduction in cell mortality by apoptosis of 25% compared to the naked eye in the spectrum range [400 nm, 450 nm]. Figure 4 shows the comparative levels of apoptosis between the naked eye (grey) and Crizal^® Prevencia^® (purple) for each of the bands of blue illumination. This level of protection would therefore mean a reduction in the long term in the cumulative risk linked to harmful blue light and therefore the onset of AMD.

Fig. 4: Comparative results between Crizal Prevencia and the naked eye of RPE cell death by apoptosis, exposed for 18 hours in vitro to normalised sunlight for a 40 year old human eye.

The combination of the UV barrier provided by the material and the anti-reflective coatings on the back side of the lens offered 25 times more protection against UV rays, compared to the naked eye (E-SPF 25).

CRIZAL^® PREVENCIA^®, THE EVERYDAY PREVENTION SOLUTION

The new Crizal^® Prevencia^® lens therefore reduces the damaging, cumulative effects of harmful lights (Blue-Violet and UV).

This preventive lens is for everyone, and specifically for more particularly vulnerable populations such as children and adults aged over 45.

- Before the age of 10, the eye's extreme transparency allows bands of harmful light to penetrate more deeply. The retinal cells are therefore more highly exposed to UV rays and Blue-Violet light.

- After the age of 45, the eye's defence system weakens and the sensitivity of retinal cells increases. This means that the risk of eye disease increases.

Crizal^® Prevencia^® can also be combined with a photochromic technology used to obtain optimal protection for outdoor activities whi lst offering the desired transparency for indoor wear.

• When the lens is clear protection against Blue-Violet light is reinforced thanks to additional absorption by the photochromic pigments.

• When activated the photochromic lens is tinted and protection is then at its maximum, at over 80% whatever the material used.

Crizal^® Prevencia^® is the ideal preventive solution against the dangers of harmful light, which are still relatively unknown amongst the general public. The role of vision professionals and Essilor is therefore key in creating awareness and recommending this product.