Eye Care Blog

More familiar to us are X-rays, harmful to our tissues in large doses. They can cause cataract and retinal damage. In practice X-rays used for diagnostic purposes are of low dosage, and their effects, both as regards the patient and the practitioner, are controlled. In high intensity they can be used in narrow beams to burn away tissue. (Laser is an example of concentrated light rays.) If such beams are directed on the eye, immediate and irreparable damage would be done. The eye is designed to cope with normal light, i.e. that part of the light (electro-magnetic radiation) between the infra-red and ultra-violet parts of the spectrum. The spectrum extends considerably further in each direction, and the eye can only absorb small low-dosage radiations from these outer areas. In outer space such radiations abound, but the earth’s atmosphere acts as a screen protecting us from harmful rays.

Ultra-violet light is manufactured by the sun, but it can also be produced artificially by passing high-voltage electrical discharges through inert gases (hence ‘UV tubes’). In high doses ultra-violet light can cause severe tissue damage. In low doses, however, the human skin absorbs the rays by producing vitamin D. (This is how the skin `tans’.) The cornea can react violently to an overdosage, with symptoms typical of ordinary heat burns. It should be remembered that most glass spectacles absorb the harmful rays, but plastic spectacle lenses, unless specially made, do not. Again, the plastic of contact lenses does not absorb ultra-violet light, and so it is particularly important that all contact-lens wearers use sunglasses in strong sunlight.

Infra-red light is at the end of the visible light spectrum. It is the name for heat rays emitted by very hot burning elements — for example, from furnaces and from objects that have been heated by a blow-lamp. Infra-red is mostly absorbed by the tissues of the eye, but if the dosage is high enough damage may be caused. Exposure to infra-red light over a long period of time can also affect the crystalline lens, causing cataract. Indeed some researchers firmly believe that infra-red and ultra-violet light is the chief cause of cataract wherever it occurs.

Both infra-red and ultra-violet rays are used for artificial `sun-bathing’. In recent years sun parlours have enjoyed considerable commercial success, so it is important that clients of such establishments should be made aware of some very real risks they take. Of the two, infra-red is the less harmful, the lesser of two evils one might almost say. It is used to heat the body and — providing the eyes are not over-exposed, either in terms of time-period or proximity to the heat source — lasting damage is unlikely to be incurred. But over-response, especially in individuals with sensitive skins, can produce burns to the surface of the eye. These are usually minor, and any discomfort quickly recedes. Infra-red light does not significantly tan the skin, and, although pleasant enough to lie in, is most often used for therapeutic or semi-therapeutic purposes (e.g. for the alleviation of lumbago).

Ultra-violet light is another matter entirely. As has already been said, it produces a skin reaction that encourages the production of vitamin D in the surface tissues of the human body, and this leads to the tanned effect. There is a narrow range within which it is considered safe to use such rays. Outside that range the skin and deeper tissues can be burned, and this applies to the eyes as well. Ultra-violet light comes in two sorts, UVA and UVB. It is said, with some justification, that the second is less harmful than the first. But while this may be true, it is technically very difficult to produce a pure separation of the two kinds of ultra-violet light (which are in close proximity in the spectrum), and so a `UVB machine’ may also be inflicting a significant dosage of UVA. In general, UVB is likely to cause only surface damage to the eye, while UVA can cause internal damage. Such burns have a delayed pain response.

There are also other aspects of ultra-violet light usage, such as the possible incitement of skin cancer, and which are still subject to intense medical research and debate. However, as far as the eyes are concerned, it is firmly recommended that, to avoid photo-chemical injury, efficient eye-goggles be used at all times during sunlamp treatment of whatever kind. Manufacturers are not yet in a position to say categorically whether their instruments are harm-proof, and there are unfortunately a few unscrupulous proprietors of sun parlours who will tell their clients that their equipment is safe without this necessarily being the case. It should also be remembered that not all sunglasses are efficient at screening out harmful short-wave rays, and it would again perhaps be prudent for the artificial sunbather to check whether the goggles provided really can do what is required of them. On the principle of better safe than sorry it should perhaps be suggested that there is no such thing as a safe sunlamp without the use of optically sound protection.

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