Prevencia lenses are photochromic
Blue blockers in contact lenses - more than a niche in the future?
There is certainly no undisputed answer to the core question of this article from the point of view of the optical industry, opticians, ophthalmologists and ophthalmologists. But "they" have been around for a long time and there is increasing interest when it comes to the subject of blue light protection and optical visual aids.
As a manufacturer of a very large variety of high-quality, soft and dimensionally stable individual products, based on our own material research and polymer production for all contact lens materials, this question has been a topic at Wöhlk for many years and has already been researched with different goals. Against this background, some aspects are conveyed from an optical and material-chemical perspective and the medical biochemical effects are deliberately hardly touched, especially since the state of knowledge is high but not entirely clear.
1) Visual aids with blue blocker
For modern visual aids (glasses, IOL and contact / scleral lenses) the protection or filtering of spectral “blue light” is a kind of “descendant” of the ubiquitous UV protection, which is standard for glasses and for the various lens products on / in the eye is also very common. The contact lens manufacturers sometimes offer very good or good UV protection (UV-A and UV-B). However, there are still many well-known materials and products that do not have a UV absorber. If there is no information on the product, you should therefore inquire if necessary. In contrast to the known risks of unfiltered UV radiation on the eye there is no equivalent concern for the wavelengths of violet and blue light. Nevertheless, there is uncertainty about the “healthy dose” and the risks of long-term increasing exposure to blue light (photostress), e.g. due to the increase in the daily use of artificial blue light sources (LEDs, monitors, smartphones).
In the literature, the wavelength range from 380 to 500 nm is often referred to as the blue light range. It is by no means the aim for IOLs or contact lenses to filter out this entire area of light if necessary and to reduce it as much as possible to protect the eyes, as is certainly justified with sunglasses. Rather, it is about the preservation of very relevant radiation, especially in the range of 480nm (blue-green). This area is sensitive for the synchronization of the internal biological clock and for the control of the pupil contraction. In contrast, the very high-energy wavelengths of the blue-violet range from 380 to approx. 450 nm with increased exposure are a possible cause of age-related macular degeneration (AMD) after cataract operations[2;6]. From a global perspective, many people are increasingly exposed to the risk of phototoxic eye disease. Numbers of around 3.2 billion are given[1;4]where the risk groups are children and adults over 45 years of age.
Fig. 1) Color spectrum of visible light
Since the current state of research shows a connection between exposure to blue-violet light and, in particular, accelerated AMD, although there is still no definitive evidence, there is slowly growing interest in products with more or less blue blocker components. The topic is gaining more publicity due to the increasing marketing of glasses with blue filters, but has also been available in selected lens products for many years.
2) Material concepts for filtering blue light in IOLs and contact lenses
The IOL products initiated research studies well before the contact lenses for the reasons mentioned (AMD protection after cataract) and are in an intensive discussion about the meaning and benefits of these lenses with blue light filters[2;3;6]. There is a clear increase in the variety of “yellow” IOLs, which are now available either as permanently yellow-colored lenses, or on the basis of a photochromic dye, which then colors the lens yellowish with a very short time delay (10s) when exposed to light and achieves blue light protection, and becomes colorless again within 30s in low light and darkness[5;10]. The required dyes in the materials are insoluble as raw material additives during production and are therefore permanently integrated in the polymer network. In the case of the photochromic IOL, an approx. 50% blue light protection is indicated.
For almost 10 years there have also been yellow blue filter lenses in the field of modern contact lenses, but these have been developed for reasons of improving visual acuity and better contrast vision. In this product niche there are the so-called sports lenses (Fig. 2), which are available in three color variants, in a large parametric selection, as modern replacement lenses made by Wöhlk.
Fig. 2) Sport Contrast for indoor and outdoor use
In order to achieve the unavoidable yellow color of a blue light filter lens that is a little less noticeable on the eye, the lenses are lavishly tinted without coloring the edges. The lenses were primarily developed for customers with sporting ambitions, but also very clearly absorb the high-energy violet-blue light (Fig. 3) and can therefore also be recommended for customers with an increased need for AMD prevention. It should be noted that these lenses absorb most of the violet light (> 50%).
Fig. 3) Light spectrum contact lens Wöhlk SPORT Contrast yellow
If the yellow tint of the lenses is an unacceptable color for cosmetic reasons, no good or very good blue light protection can currently be offered as a contact lens. Products that should remain almost unchanged in color, i.e. either completely colorless or only contain a very slight mostly green or bluish handling tint, cannot achieve good (≥50%) protection against blue light for physical reasons. In contrast to UV protection, where the UV absorber content of the contact lens cannot be “seen”, a very light-colored contact or IO lens is an indication of a very low level of protection against blue light. The color depth of the lenses and the resulting light protection are of course also dependent on the lens thickness, since the light transmission follows the Lambert-Beer law. High plus lenses will therefore have measurably more protection against blue light than minus lenses. Usually, comparative tests are also carried out for UV protection and other material properties on weak minus lenses (e.g. -3.00dpt).
The first lens products are already coming onto the market with reference to UV and blue light protection. These lenses are very light yellow in color, presumably in order not to expect the customer to have a noticeably yellow lens on their eyes. The blue light protection provided by these lenses is correspondingly low (<20%).
In the area of medical contact lenses (Fig. 4), which are manufactured and colored in many variants at Wöhlk, these cosmetic aspects have no priority, so that these very dark brown or sometimes black products as edge filters and glare protection always also include UV and ensure full protection against blue light (custom-made).
Fig. 4) SP contact lens RP / SP contact lens
The cosmetic colored lenses for changing the personal eye color have also been an option for many interested parties for decades. Here, more color depth is also an indirect effect that leads to blue light protection. In the case of Wöhlk colored lenses of the Weflex color type, this results in approx. 10 to 60% protection against blue light, depending on the color and depth of color chosen.
2.1) Structure of a blue blocker
As a material additive, blue light protection is best achieved by adding a suitable amount of a derivative of the 4-phenylazophenol type (Fig. 5).
Fig. 5) PAP (4-phenylazophenol)
A permanent, chemically stable integration into the polymer network of the contact lens can only be achieved through a polymerizable modification as an acrylate monomer (Fig. 6).
Fig. 6) chemical structure of a blue blocker (2-propenoic acid, 2-methyl-, 4 - ((1E) -phenylazo) phenyl ester)
This copolymerization of a blue blocker is then stable over the long term and has no handling restrictions. On the one hand, the chemical structure of a phenylazophenol has the desired absorption properties, but in addition to a yellow coloration of the material, with increasing weight percentage it also causes changes in the mechanical lens properties (hardness, modulus, etc.). The patent literature describes numerous possibilities and also modifications of the structures shown on the subject[11,12,13].
In order not to have too strong influences or other unwanted side effects on the material, it makes sense to polymerize with relatively small amounts of a blue blocker or not to change the material in such a way, but to color lens products in a very defined way. A more complex subsequent covalent integration of very small amounts of dyes into the material network (Fig. 2, 3, 4) can also achieve a high level of protection against blue light if required.
In contrast to UV protection, there is currently no strong need for contact lenses to introduce blue blockers into the material. Efficient filtering is only achieved with clearly colored, mostly yellow lenses and thus less attractive lens colors. The chemical integration has been achieved for years using high-quality raw materials or special dyes, both for hydrogels and for dimensionally stable RGPs, and is available, among other things, in the modern sports lenses mentioned. These products have the special advantage that they are not colored in the lens edge area and are therefore significantly less “noticeable” to the eye. The question of the benefit, which is still being discussed, could certainly change in the future if there is more and more exposure (photostress) from violet-blue light. At present, these are still niche products, which is to be assessed very differently in the case of IOL products, and which are more motivated by the numerous study results to offer opportunities for more AMD protection.
Roland Fromme; Head of materials research
Wöhlk Contactlinsen GmbH
Contact for Austrian contact lens fitters
Wöhlk-Contact-Linsen Vertriebs GmbH
Telephone +43 (3682) 23065
Fax +43 (3682) 23045
Email: [email protected]
- Bütikofer K .: Harmful blue light and UV protection. Swiss Opticians 2014 (3), 19
- Heiting G .: Blue Light: It's Both Bad And Good For You. AAV Media, LLC www.allaboutvision.com (CVS / blue-light.htm 2017
- Mester U. Prof. Dr .: Does the blue light filter in the IOL make sense? Ophthalmic News 2016
- Bargetzi Y. Crizal Prevencia UV: Essilor introduces preventive lenses with selective protection against harmful blue light and dangerous UV radiation
- MATRIX aurium; http://www.aivimed.de/patienten/katarakt-3/matrix-aurium/
- Augustin C .: Blue Filter Intraocular Lenses, An Update; Concept Ophthalmologie 02/2015 (19-21)
- More than standard: Augenlicht 4/2013 (14/15)
- Hedrich M .: Good night everyone! Blue light keeps us awake, Global CONTACT 1-16 (26-29)
- Loperfido F., Marchese A .: Clinical Evidence and Benefits of Filtering Harmful Light, Points de Vue - International Review of Ophthalmic Optics 07/2016 (1-5)
- Avalos G .: Two-Year Clinical Experience With a Photochromic IOL, Cataract & Refractive Surgery Today Europe 07/08 2008 (22/23)
- EP 2247976 B1: Ophthalmic Lens Having a Yellow Dye Light Blocking Component
- US 8,047,650 B2: Ophthalmic devices having a highly selective violet light transmissive filter and related methods
- US 2006 / 0241263A1: Novel reactive yellow dyes useful for ocular devices
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