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Safety Lenses 175

injuries. Radiation injuries involve damage to the eyes as a result of
absorption of harmful radiation. UV radiation can affect both the skin
and the eyes. Pingeculae, pterygium and band shaped keratopathies are
thought to be caused partially by long term chronic exposure to UV
radiation. Cataracts are also thought to be caused by absorption of UV
radiation. Visible light may also cause damage by thermal photocoagul-
ations. Retinal burns may occur when high intensities of light are focused
on the retina. Infrared radiation, when absorbed, leads to thermal effect
on the tissue.
These ocular hazards are associated not only with industrial occupations,
but also with sports, leisure activities are on the increase. In USA, the greatest
number of injuries results from base ball, ice hockey and racket sports.
Racket sports are responsible for many ocular injuries, and this is not
surprising, given the speed of the ball. A squash ball may reach speed of
224 km/hour, a tennis ball 192 km/hour and a shuttlecock 232 km/hour.
There is also the risk of the player being hit by the opponent’s racket. Many
severe ocular injuries occur to children at play and in the home and at
times such accidents become the major cause of blindness.
Many of such ocular hazards can be prevented by widespread use of
eye protectors in the form of safety glasses. Tinted lenses protect the eyes
from harmful radiations. It may also be necessary to protect the eyes against
the other ocular hazards, arising from dust, flying particles, industrial
environment, sports injuries etc. Legislation is now there to protect the
eyes both in the work environment and in certain sports, such as squash
and protection may need to be provided, whether the lenses include a
refractive correction or not, in the form of safety glasses.
Safety glasses provide protection against impact, chemical or molten
metal splashes, dust or radiations from welding arcs of lasers. It may take
the form of spectacles, goggles, visors, face shields or hoods. Good safety
glasses are made from polycarbonate and are shatter resistant. This does
not mean they are unbreakable or that they will last for ever. Their purpose
is to protect the wearer from injury from accidental projectiles and particles.
As the lenses become exposed to more and more bits and pieces of materials
over time, they will become pitted. The more pitted they become, the less
clear the wearer will be able to see things. More importantly, after a while,
the bombardment of particles will weaken the lens and they should be
replaced. Most safety glasses also provide a high level of UV protection
and therefore, can be used as sunglasses.