The last decade has seen major innovations in clear everyday lenses with the incorporation of evolving photoprotective technology. Essilor’s photoprotective research programme started about 10 years ago, delivering in 2011 the first anti-reflection coating with low UV reflection on the rear surface with Crizal UV.
Thanks to the collaborative research program between the Paris Vision Institute and Essilor, the Crizal Prevencia coating was released in 2013, the first clear lens to integrate an antireflective coating that blocks both UV and partially harmful blue-violet light while maintaining transmission of the essential blue-turquoise light.
This year brought Essilor’s latest technological advance, the Smart Blue Filter, a novel development using embedded blue-violet light protection, compatible with any anti-reflection coating. The Eye Protect System lens brings together the Smart Blue Filter and UV protection while ensuring minimal aesthetic compromise. For extra protection, the Smart Blue Filter lens has been combined with the Crizal Prevencia coating.
Refining the test system
The photoprotective effect of the Smart Blue Filter lens feature was compared between each narrow illumination band within the blue-violet range from 400 to 450nm to better differentiate the different spectral profiles.
To validate the photoprotective effect in real light conditions, a polychromatic light source (as opposed to the monochromatic light source used in the in vitro model) was incorporated.
Over an 18-month period, researchers at Essilor developed an innovative adjustable fibred white light illumination device which can generate programmable and variable spectra and irradiances within the visible range. This new device offers greater flexibility than the previous blue-green light device, delivering any specified part of the spectrum within the visible range. Thus, in addition to daylight spectra, it can also mimic warm-white or cold- white LED, fluorescent, and incandescent spectra, and even quasi-monochromatic light. The photoprotective potency of the Smart Blue Filter lens feature was measured in terms of the reduction in apoptotic cell death with the filter versus without.
UV protection: The E-SPF Index
UV is a constant source of potential eye damage irrespective of the weather conditions. Exposure occurs directly from the sun’s rays. However, more than 50% of UV radiation reaching the eye is indirect, coming from cloud scatter and reflection.1 Public awareness of UV eye hazards has been increasing since the widespread introduction of UV SPF campaigns to protect against skin cancer.
Most clear lenses provide a high level of UV protection by absorption. Crizal Forte UV coating offers additional UV protection on the back surface of the lens to limit UV reflection that might otherwise reach the eye.
The E-SPF (eye-SPF) index takes into account both UV transmission through the lens and UV reflection off the back surface of the coated lens, although it does not account for light coming around the lens or for variations with facial morphology, gaze direction and glasses shape. Essilor is currently offering an E-SPF of up to 35 on clear lenses.
Global protection
The Smart Blue Filter innovation was designed to distinguish harmful blue-violet light from essential blue-turquoise light, absorbing the former and transmitting the latter, using specific absorbers for blue-violet light, embedded inside the lens such that blue-violet light reaching both the front and the back surface of the lens is filtered (figure 1).
This new embedded innovation offers the key advantage of being compatible with all anti-reflection coatings. Building on the existing Crizal UV coating, Essilor combined the embedded Smart Blue Filter feature with E-SPF, offering a clear lens with both UV and blue-violet protection called Eye Protect System.
As such, the lens filters on average 20% of the blue-violet light between 400nm to 455nm, combined with UV protection (figure 2). Its blue light photoprotective effect on retinal cells (RPE) in vitro is equivalent to that offered by Crizal Prevencia coating giving a 25% (±5%) decrease in retinal cell death.
Figure 2: Effect of colour neutralisation on transmittance through lenses of 1.5-index CR39 plano (2mm centre thickness)
No aesthetic compromise
The absorber filtering partially blue-violet light attributes a natural yellow-orange colour to the lens which is not acceptable for a clear day to day lens. To counteract this, two neutralising molecules were added to the Smart Blue Filter. To assess the accuracy of transparency, a sensory analysis with trained judges was performed evaluating four parameters; lens colour (through the lens for the wearer), skin colour (through the lens for the observer), lens transparency (through the lens for the wearer and observer), and perception of a colour picture (through the lens for the wearer). All parameters consistently rated better for the neutralised lens than for the yellow-orange one.
Transmittance was almost identical between a yellow-orange lens and a neutralised lens (figure 2). In addition to the sensory analysis, a consumer test was performed to assess the acceptance of this new lens without explanations on the additional benefit brought. After one month of wear, 96% were satisfied by its aesthetic. This test shows that the new embedded technology is not noticeable by wearers.
Essilor Ultimate Protection
Combining the embedded Smart Blue Filter feature with the Crizal Prevencia anti-reflection coating gives a maximised protection; blue-violet and UV reflection off the front surface with Crizal Prevencia coating, partial blue-violet and UV filtration by the Eye Protect System lens itself, and minimisation of UV reflection off the back surface of the lens with Crizal Prevencia coating (figure 3). Combining these two solutions of blue-violet filtering offers a maximised protection for a clear lens, filtering on average 30% of blue-violet light (1.59 index lens) between 415nm and 455nm and reducing retinal cell apoptosis by 35%, approximately 10% more than with Crizal Prevencia coating alone.
Figure 3: The Eye Protect System lens combined with Crizal Prevencia coating ensures filtering of harmful UV and blue-violet light protection while ensuring transmittance of longer wavelength blue light
The Eye Protect System lens with Crizal Prevencia coating offers a transmittance profile filtering the greatest proportion of the harmful blue-violet light while allowing the beneficial blue-turquoise light through (figure 4) with comparable lens aesthetics to Crizal Prevencia coating alone.
Figure 4: Transmittance curves of a range of Essilor lenses
Coralie Barrau is a research engineer in optics and photonics, Amélie Kudla is R&D innovations programs co-ordinator and Mélanie Tessieres is an R&D optical engineer for Essilor.
References
1 Sliney DH. Geometrical assessment of ocular exposure to environmental UV radiation--implications for ophthalmic epidemiology. J Epidemiol.1999;9(6 Suppl):S22-32.