Environmental Engineering Reference
In-Depth Information
Figure 1.
The human eye
2. Effects from environmental exposure
Human exposure to sunlight, particularly the UVB component, is believed to be
associated with a variety of eye disorders, including damage to the cornea, lens and
retina
4
. Photokeratitis (snowblindness) is clearly related to UVR exposure, whereas,
cataracts (opacities of the lens) are the most frequently cited delayed consequence. Certain
keratopathies (corneal degenerations) and pterygium (a fleshy growth on the conjunctiva)
also are believed to result from excessive UVB exposures. Cataracts are a major cause of
blindness in both developed and developing countries. However, the relative importance
of different wavelengths in cataractogenesis, as well as the dose response curve, remain
uncertain
4,9
.
The geographical variation in the incidence of age-related ocular changes such as
presbyopia and cataracts and diseases such as pterygium and droplet keratopathies have led
to theories pointing to sunlight, UVR exposure and ambient temperature as potential
etiological factors
5,9,10
. Some epidemiological evidence also points to an association of
age-related macular degeneration (AMD) to sunlight (particularly blue-light) exposure
11
.
The actual distribution of sunlight exposure of different tissues within the anterior segment
of the eye is more difficult to assess than one would expect. Of greatest importance are the
geometrical factors that influence the selective UVR exposure to different segments of the
lens, cornea and retina. Studies show that sunlight exposure to local areas of the cornea,
lens and retina varies greatly in different environments. Perhaps for this reason, the
epidemiological studies of the potential role of environmental UVR in the development of
ocular diseases such as cataract, pterygium, droplet keratopathies and age-related macular
degeneration have produced surprisingly inconsistent findings
7-9,12
. All of these ocular
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