The dangers of excessive ultraviolet radiation (UVR) exposure are now well known to many of the population, but evidence of UV damage is often seen, so why is this? If we look at skin, for example, it is the widely held desire of many individuals to obtain a sun tan, despite the fact that this is evidence of damage to the skin. A particular problem here is that ‘dosages’ are difficult to control and monitor when exposed to the sun, and the harmful effects are subject to time delay. In the case of the eye, skiers may suffer from temporary ‘snow blindness’ due to UVR.
The effects of UVR are very much dependant on time and wavelength. Thus very short wavelengths (eg. Excimer lasers, circa 190 nm) are used for shaping the cornea in photo refractive surgery, and this can be carried out in a matter of seconds. However long wavelength UVR in the range of 370 nm has a long term effect over a period of years and can affect the crystalline lens of the eye.
So how is UVR classified? It is common to describe three bands:
UVA 315 to 380 nm
UVB 280 to 315 nm
UVC 100 to 280 nm
Note that the precise band boundaries vary with different authorities, so that UVA, for example, is described by the CIE as going up to 400 nm. Indeed protection from wavelengths up to 400 nm has now become an important marketing issue for ophthalmic lens manufacturers, despite the fact that standards for ophthalmic lenses and sunglasses only cover radiation transmittance in the 280 to 380 nm range. UVR les than 280 nm (UVC) is not considered in the standards, as this range is first of all filtered out by the earth’s ozone layer, and secondly is not transmitted by any of the commonly used ophthalmic lens materials.
UVC can be produced not only by the sun, but also by some artificial light sources, for example arc lamps. There is anecdotal evidence that in the early days of the cinema industry, unshielded arc lamps caused actors to have watery red and painful eyes, as a result of exposure to UVC. This hazard was removed by simply placing a clear glass cover over the arc lamp.
Thus the longer the UVR wavelength, the further into the eye it will penetrate, and in general the longer the effects take to be noticed. Studies have shown that individuals working outdoors for many years can be more predisposed to developing cataract , and there is even some evidence of a tendency to macular degeneration. The World Health Organisation has estimated that 20% of the cases of worldwide blindness due to cataract are caused by exposure to sunlight. As aphakic eyes have no crystalline lens to absorb the UVR, it is now common practice for intraocular implant lenses to contain a UVR blocking filter to protect the retina.
It is not only inside the eye that problems can occur. Long term exposure to sunlight can give rise to conjunctival defects such as pinguecula and pterygium. The latter can grow across the cornea in extreme cases.
It should be remembered that besides the effect of sunlight, there are many sources of UVR in everyday use, particularly in the workplace. It is self-evident that in these cases adequate shielding and protection should be given to the workers involved, for example in electric arc welding. Specialist UVR emitting lamps are also now commonly used in medicine and industry, often for curing adhesives.
Standards for eye protection from UVR exist not only for sunglasses but also for prescription spectacles . Although the potential dangers of UVR exposure have been known for a very long time, it is only relatively recently that standards have become developed. The first sunglass standard was produced in the UK in 1956 , and since then others have been developed, significantly by CEN in Europe , ANSI in the USA , and also in Australasia . Sunglasses are now major items of international trade so it is appropriate that an international standard (ISO) for these items is in an advanced stage of development.
Exposure to UVR is essential for the skin to produce vitamin D, and a recent study  has proposed minimum standards for exposure to sunlight. But excessive exposure can cause degeneration of the skin cells, blood vessels and fibrous tissue leading to premature ageing, and in some case, skin cancer. It is particularly important to educate young people in this regard. One device that can be useful is a simple wrist monitor (Transitions Optical) which darkens depending on the level of UVR intensity (Fig.1)
Fig. 1: Wrist band for detecting UVR intensity. Compare the central colour with the surrounding key values (Transitions Optical).
One area of skin that is often forgotten in relation to protection from UVR is that around the eye. It can often be assumed that sunglasses will protect this area, but unless of the close-fitting wraparound variety this is not always true.
The dangers of UVR have been known for a long time. A 1911 ophthalmic lens catalogue from Groos Ltd of London advertised a protective lens (‘Antactin’) noting that ‘prolonged exposure to ultraviolet light is exceedingly harmful’. Despite this, it is still necessary to educate the population of the dangers of UVR and provide improved protection from the harmful effects.