Good eye protection is essential for every water sports enthusiast. But what makes a good pair of sunglasses? They must not only reduce visible light, but also block harmful ultraviolet radiation. Reflections on the water intensify both effects. Sunglasses for use on a boat are therefore more specialised and more important than those for everyday use on land.
Ultraviolet radiation is more energetic and more damaging to the retina and skin than visible light and infrared light. UV light can cause sunburns, even in the eye. Radiation in the UV-C range has the most energy. For technicians: these are wavelengths between 180 and 280 nanometres. "UV-C radiation from the sun is completely filtered out worldwide. Without this filtering, there would be no life on earth," explains Cornelia Baldermann, an expert in UV protection at the Federal Office for Radiation Protection. According to the expert, the atmosphere also filters out the majority of UV-B radiation, i.e. wavelengths between 280 and 315 nanometres. Wavelengths of 315 to 400 nanometres correspond to UV-A radiation.
One detail: With thinner air at high altitudes, UV radiation increases, 15 per cent per thousand metres, so Himalayan aspirants receive significantly higher UV doses. The radiation on snow is also eight times as high as on a meadow. And it is still twice as high on water. Going snow-blind on the water? Yes, it is actually possible if there is enough radiation. The term "snow blind" is somewhat trivialising, as it is actually an eye injury, a sunburn on the cornea and conjunctiva. The irradiated cells die and the surrounding cells react with inflammation. Symptoms often only appear four to ten hours after sailing in the sun and last for twelve to 48 hours, sometimes longer. Berths and cabins then help. UV radiation in wave bands B and A is so strong that it can ban crew members from the deck and affect sailing plans.
Children and people up to around 30 years of age are particularly at risk, as around ten per cent of UV-A radiation affects the retina up to that age, and one to two per cent later on. "The number of hours of sunshine is increasing overall, and we are seeing very sunny years, which means that the amount of UV is increasing, but the UV intensity has also increased by several per cent in recent years," says Cornelia Baldermann, explaining the observations of the Federal Office.
Not every pair of sunglasses is suitable for days out on the water. It depends on the fit - and even more on the lenses. After all, the once notorious cornea-eaters are hardly in circulation today. There were actually such rugged sunglasses with lenses made of real glass. However, glass allows 60 per cent of UV-A rays to pass through, and the dilated pupils caused by the tint open the door to further damage. Various plastics are available today, but the names are confusing. Lenses for sports sunglasses are now predominantly made of polycarbonate. Less UV radiation penetrates the material. Alternatively, lenses made of acrylic glass are available, which are more transparent but softer and scratch more easily.
Then there are lenses made from polyallyl diglycol carbonate. No optician calls it that, but advertises glasses made of CR39, the brand name of a US manufacturer. In 1940, synthetic resin was traced in the States. 180 samples were researched, number 39 impressed with its favourable properties, and the USA initially used the new material in bomber searchlights. "CR39 only has low UV protection with a cut at 360 nanometres," says Florian Gisch, Managing Director of Wetzlich Optik, explaining the parameters of the glass options. Additional UV protection must therefore come from the colouring. He adds: "Polycarbonate, for example, already offers UV protection up to 380 nanometres as white glass."
Trivex, another lens option made from polyurethane, also has good UV protection already in the material, but has a lower refractive index than polycarbonate. It is therefore lighter, but for the same visual acuity, optical lenses have to be ground thicker, which sometimes cancels each other out. Finally, triacetate cellulose (TAC) is very light, clear and the lenses are said to be particularly easy to polarise, although they are less scratch-resistant. Lenses made from all these plastics are very robust and refract light well, but are not scratch-resistant.
The material is also sensitive to salt and does not like solvents, which are often contained in sun creams. Opticians recommend a microfibre cloth for the care of all glasses, which should be washed often and without fabric softener. They also recommend cold water with washing-up liquid and towelling with a cotton cloth. Damp glasses cleaning cloths or cleaning sprays? Better not, say the experts.
The lenses must therefore partly reduce and partly block radiation. 50 per cent of sunlight is visible, which is where tinting helps, while 44 per cent is infrared radiation, i.e. heat. "I don't know anyone who has gone blind from natural infrared radiation, but there is no question that heating the eye for a long time does not contribute to its longevity," and there are indeed coatings that shield against infrared radiation, says optician Florian Gisch.
The UV component at the other end of the light spectrum is only six per cent, but this high-energy part packs a punch. There is a European standard, Din EN Iso 12312, and since 1995, glasses or goggles have had to comply with this standard, which is then labelled with a CE mark. The standard requires a complete UV blocker, but only up to a wavelength of 380 nanometres. This applies to the UV-A range, but not the entire range. UV-B radiation is filtered by all standardised sunglasses, and UV-C radiation is already shielded by the atmosphere. But there is still a gap.
Cornelia Baldermann from the Federal Office recommends radiation protection up to 400 instead of just 380 nanometres, which marks the transition from ultraviolet radiation to visible light, because sunglasses manufactured according to the standard can filter out UV radiation down to just 370 nanometres due to measurement uncertainties. "We therefore recommend sunglasses labelled UV400," she says. These produced good results in random tests, but "both expensive and cheap glasses without UV400 labelling often only filtered out UV radiation up to 380 nanometres or even 370 nanometres in our non-standardised test".
The UV400 label is worth nothing. There is no definition, verification or at least a voluntary commitment. The Central Association of Opticians puts us in touch with the optician Katja Grimme, who sells sports glasses: "As short-wave radiation is considered harmful to the eye, protective lenses with UV400 are supposed to be safer," she says, "but this is questionable due to the marginal difference."
For the CE mark, manufacturers only provide one copy for testing. What's more, counterfeiting is easy. "We often see cheap imitations of branded glasses sold on markets outside the European Union," says Katja Grimme, "the workmanship, logos, material and models outside the collection allow us to draw conclusions about counterfeits, which usually have no UV protection." A tip on this: Some opticians have UV testers in the laboratory or on the counter that cover a spectrum of up to 400 nanometres; the reading must drop to zero per cent for good glasses.
At least the experts agree on tint and colour. There are five classes for sunglasses, class zero corresponds to tints of up to 20 per cent. Class one and two glasses are also only suitable for shadows and have tints between 20 and 82 per cent. Class three refers to tints between 82 and 92 per cent, while class four goes up to 97 per cent tint, i.e. glacier glasses. Class three and four fit on board. Brown and grey are well suited as tint colours.
A yellow filter blocks out blue colours but improves contrast. Water reflects, a vertical polarisation filter deletes the reflections for an additional charge. The disadvantage: LC displays on plotters or instruments are somewhat more difficult to read.
Sunlight also reaches the eye around the frame as scattered light. Curved lenses provide the best shielding. These frames curve around the head. If you don't like this Harley biker style at all, you can find frames for racing cyclists or glasses with wide temples. As an alternative: a peaked cap or wide-brimmed sun hat.
If you pay attention to the points described above when buying, you'll be travelling safely and well. Aspects such as fashion and personal taste will certainly play a major role in the purchasing decision. Fortunately, the choice is wide and the customer is not limited to suppliers from the water sports sector. Manufacturers from the cycling, mountaineering and skiing sectors in particular offer a wide range of good products that are also suitable for use on board; everyone should be able to find what they are looking for.
However, it is more difficult for 67 per cent of people over 16 and 91 per cent over 60 who wear glasses. If you want optical sunglasses, you have to choose the model and lenses, but first you have to consult an optician. Can they do anything with the following values? Firstly, the pupillary distance (PD), which is also necessary for all everyday glasses. Then the forward tilt (VN) of the frame is decisive and the corneal vertex distance (HSA), i.e. how obliquely do the lenses sit and how far are they straight ahead from the pupil?
The curved design is particularly suitable for water sports goggles as it reduces stray light, see above. This results in a different correction than for everyday glasses. The values for such frames are the frame lens angle (FSW) and the lens curve or base curve (BC), which can also be measured without the wearer. Opticians who are creative with these values are good because they are helpful. Unfortunately, the usual spectacle specialist is often not enough. The expert for ordinary varifocals is not necessarily familiar with optical sports glasses. "People actually come to us in Bielefeld from further afield," explains Jens Heymer (www.sport-brille.de) specialises in sports sunglasses, "but I also recommend a few colleagues across Germany who also provide very good advice."
A second option is to feel the optician's lens with specialised or trick questions from above. Such a search can be carried out, for example, on the website of www.sehen.de and tick the "Sports glasses" box. On site, it can help to ask whether existing sunglasses can be measured once. Measuring devices such as the "Opti-Scan" determine the UV light between 320 and 400 nanometres and also the tint.
If you don't like travelling or searching, you can fall back on a special service. R & F Sportbrillen GmbH in Berlin offers sunglasses from various brand manufacturers with optical correction especially for water sports enthusiasts, cyclists and hikers (www.die-sportbrillen-shop.de). Firstly, the measurement data of the everyday glasses must be entered into an enquiry form. "We use the data to check the feasibility," says the provider. Anyone who places an order is sent a pair of measuring glasses with a camera to their home and instructions on how to take the photos. "These images are the basis for calculating the glasses," reports Managing Director Frank Immervoll.
Around two to three weeks later, his company sends the glasses with a six-week "compatibility guarantee". If the incompatibility is not due to incorrect input values, customers can return the glasses or optical clip, but in more than 99 per cent of cases the glasses fit. Such customised optical sunglasses cost just under 300 to 900 euros.
There are several types of optical sunglasses. On the one hand, these are attachable lenses that are slid in front of everyday glasses. Very classic shapes with a metal clip can scratch the optical lenses, while modern models provide additional lateral shielding. For on-board use, prefabricated glasses with optical fields of vision are available, which can at least replace reading glasses with the same dioptre distribution in both eyes.
Another solution for spectacle wearers is photochromic lenses that darken themselves. These self-tinting lenses react to UV radiation within half a minute. Some lenses are said to darken up to 92 per cent. This turns everyday glasses into sunglasses. A residual tint remains in the dark, which you have to like. For one of the opticians we contacted, however, such glasses would be their first choice.
There are other options for spectacle wearers: system sunglasses have a holder for the optical insert or clip on the inside. If the prescription changes, all you need to do is fit a new clip. If the actual sunglasses have an interchangeable lens system, this will continue to work. But there are also disadvantages. The field of vision of the small clips is smaller, the ventilation between the clip and the glasses is not as good, and some people bump their eyelashes against the clip lens, which sits quite close to the pupil. The clip has to be removed for cleaning. However, the system is inexpensive and also works with high dioptres. Julbo, Swiss Eye, Bliz and Demon have such clips in their range.
For spectacle wearers, direct glazing is therefore often the first choice, but also the most expensive. Some manufacturers of sunglasses offer the lenses, while others remove the existing lenses and insert other optical lenses. Especially with curved lenses, which are not just cylindrical but spherical, optician experience is required for such a selection and fitting. "If he has any doubts, then he has no idea," we heard confidently from a sports optician. Also: "The opticians at the chain stores are often not trained to fit optical sports sunglasses".
A special case of direct glazing is tinted glass that is individually clipped into an otherwise glass-free frame. This means that the tint can also vary. Glued-in optical glasses, on the other hand, are doubled on the inside of the tinted glasses. Cleaning is easier with these two variants and ventilation is better. The combination of contact lenses with conventional sunglasses has proved very successful in many cases. The glasses then also help to block out the wind, which often disturbs contact lens wearers in particular. And there is a huge selection of commercially available sunglasses to choose from, which are naturally less expensive.
A good pair of glasses, according to an often-heard rule, should not be felt at all. In fact, they shouldn't pinch, but they shouldn't be particularly loose either. This applies to all sunglasses, optical and non-refractive. When looking through the lenses, nothing should be distorted; at best, the frame should be made of rubber-like plastic that springs back.
Lifelines are worthwhile for the often expensive and above all necessary pieces: either as a tight headband or loose around the neck. A clip, as is common with caps, can also be useful. Some neoprene straps are not only particularly soft, but also serve as a goggle life jacket. So in the event of a goggles-overboard manoeuvre, the trip could be saved and the on-board funds spared.
Optician Jens Heymer: In addition to protection from visible sunlight, protection from harmful radiation, draughts, dirt and the effect of the lens colour are important criteria. Good advice from a trained optician is also important.
Every fully polarised lens is at least 50 percent grey or darker. Often also dark brown or grey-green. These lenses are designed for use in sunshine, and they block out water reflections, which are uninformative and distracting. However, this blocking can also mean that the displays of navigation devices or mobile phones are no longer easy to read.
Acrylic glass is not used. Polycarbonate is a transparent plastic that is significantly more break-resistant than normal window glass. It is also quite inexpensive and impact-resistant. Plastics such as CR39 or Trivex are used for optical spectacle lenses. Trivex is a virtually unbreakable plastic that scores highly in terms of purity and durability.
Wind protection, UV protection, sun protection, comfortable fit and a safety device to prevent loss of the glasses. Optionally with polarisation.
Every pair of sunglasses legally sold in Germany bears the CE mark, which documents that they provide optimum protection against UV rays.