Environmental Engineering Reference
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only be obtained from animal studies and the cataract is generally anterior sub-capsular,
produced by intense exposures delivered over a period of days. 20, 26-27 . Human cortical
cataract has been linked to chronic, life-long UV-B radiation exposure. 4,5,9,12 These
suggest that it is primarily UV-B radiation in sunlight, and not UV-A, that is most
injurious to the lens, biochemical studies suggest that UV-A radiation may also
contribute to accelerated ageing of the lens. 28
One area of UV cataract research is of note when considering lens exposure
geometry of both the crystalline lens and the LAL. Since the only direct pathway of
UVR to the inferior germinative area of the lens is from the extreme temporal direction,
it has been speculated that side exposure is particularly hazardous. 29-30
7. Ophthalmoheliosis--The Coroneo Effect
For any greatly delayed health effect, such as pterygium, droplet keratopathies,
cataract or retinal degeneration, it is critical to determine the actual dose distribution at
critical locations. A factor of great practical importance is the actual UVR that reaches
the germinative layers of any tissue structure. In the case of the lens, the germinative
layer where lens fiber cell nuclei are located is of great importance. The DNA in these
cells is normally well shielded by the parasol effect of the irises. However, Coroneo 28
has suggested that focusing of very peripheral rays by the temporal edge of the cornea--
those which do not even reach the retina, can enter the pupil and reach the equatorial
region as shown in Figure 2.
Figure 2. Coroneo Effect. Oblique rays striking the peripheral cornea can be refracted into the pupil
and irradiate the sensitive germinative equatorial region of the human lens. It is this region where cell
nuclei with DNA reside.
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