Ultraviolet radiation (UVR) consists of an area of the electromagnetic spectrum between wavelengths 10 nm to 400 nm. It is divided into 4 bands: UVV, UVC, UVB, and UVA (See TABLE 1). For practical purposes, UVB and UVA are the most relevant because almost all of the lower wavelengths are blocked by the earth’s atmosphere.
| TABLE 1: Types of Ultraviolet Radiation |
| Type of UVR
| Wavelength range
| Penetration into biosphere |
| UVV |
100 nm to 190 nm |
No significant penetration into the biosphere |
| UVC |
190 nm to 280 nm |
Little penetration into the biosphere, with most radiation scattered and absorbed by atmospheric oxygen, nitrogen, and ozone |
| UVB |
280 nm to 315 nm |
Greater penetration into the biosphere, with the amount dependent upon ozone levels |
| UVA |
315 nm to 400 nm |
Greatest penetration into the biosphere, with only minimal dependence on ozone levels |
UVR poses what is possibly the most omnipresent potential threat to long-term ocular health and wellness. Most UVR emanates from the sun, although there are artificial sources of potential exposure such as welding arcs and tanning booths.
UVR exposure is a constant. Certain geographic locations, seasons, and times of the day tend to place an individual at heightened risk for solar UVR exposure, but it is important to remember that the potential threat posed by UVR is always present. Generally, the highest risk occurs in the late morning/early afternoon, between approximately 10 am and
2 pm, although UVR exposure occurs even in the early morning and at dusk.
UVR intensity is increased in certain geographic areas, for example, it is stronger at higher altitudes and in latitudes relatively close to the equator. Direct sunlight actually does not pose the greatest risk for UVR—snow has the highest UVR reflectance factor, followed by water and sand.
Even small doses of UVR can pose significant health risks, both on an immediate and a long-term basis, and the delicate tissues of the eye may be particularly susceptible to these risks.
In addition to ocular disease related to UVR exposure, UVR can adversely affect acuity through light-scattering effects in the cornea and lens, producing a decrease in low-contrast sensitivity acuity.