PHOTOBIOLOGY of the HUMAN LENS
The primary function of the human lens is to focus light undistorted onto the retina. While the transmission properties of most of the components of the eye are stable, the transmission properties of the lens change throughout life, as seen in Figure 1.
Figure 1. The changes in the human lens throughout life. Pictured are at birth, 40 years and 80 years.
Exposure to the intense light of the sun can pose a particular hazard to the lens of the eye, and lead to the formation of a cataract [a clouding of the lens], which impairs vision. Both UVA and UVB exposure [Andley et al. 2004; Roberts 2001; Balasubramanian 2000] are major risk factors for the induction of a cataract, especially in those above 70 years old, because with age the eye’s ability to protect itself against light damage is compromised. Exposure to UV radiation from the reflection off of water, sand, or snow is particularly damaging to the lens of the eye [Sliney 2005; Merriam 1996; Coroneo 1990]. In addition to UV radiation alone, there are many dyes, drugs and herbal medication that in the presence of both visible light and UV radiation can induce a cataract [Roberts 2002]. This phototoxic reaction causes a very early cataract [about 40 years old].
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