Ambient ultraviolet (UV) radiation is
ubiquitous. We're all exposed to this form of radiant energy in one
form or another. UV exposures for the most part occur via solar
radiation. While we all enjoy the cosmetic and
psychological benefits of a suntan, we as eyecare practitioners need
to always be mindful of the harmful effects of UV radiation.
Potential for Damage
radiation is broken down by wavelength. UVC is classified as
encompassing 100nm to 280nm, UVB encompasses 280nm to 315nm and UVA
encompasses 315nm to 380nm (although some consider the upper extent
to be 400nm).
Electromagnetic radiation is generally considered damaging if it
contains enough energy to ionize molecules. Shorter wavelength
radiation has more energy than longer wavelength radiation does.
Thus, UV radiation has more energy than visible light and infrared
radiation do. Molecular changes can occur with as little as 3.1eV,
which is associated with 400nm radiation (although the retina is
sensitive to 380nm).
typically focus too much on UVC because the atmosphere filters it.
Most of our focus should remain on UVA and UVB, which have the most
potential for tissue-related damage. Tissue damage from UV radiation
is generally associated with photochemical processes leading to
damage that the system may repair or to damage that causes a
permanent defect or mutation.
have significant concerns for our patients regarding ocular tissue
damage caused by UV radiation. Generally, of all UV radiation to
which the eye is exposed, the cornea absorbs approximately half,
while the crystalline lens absorbs the other half.
important to note that UV radiation really doesn't reach the retina
(in phakic individuals), so our concern focuses on the anterior
segment and crystalline lens. Anterior segment pathologies
associated with UV radiation include photokeratitis, pterygium and
conjunctival squamous cell carcinoma. Cataracts are a major concern;
in particular, direct epidemiological and basic links exist showing
UVB's etiological role in cataractogenesis.
clinically assess our patients' exposure levels, including both
recreational and occupational exposures. The biggest preventive
strategies include patient education about risks and damage. Other
general recommendations include the use of appropriate clothing and
brimmed caps, proper spectacle protection (both in clear and tinted
materials) and even contact lenses.
Contact Lenses and UV Rays
spectacle lenses, there are no ANSI guidelines associated with
UV-blocking contact lenses, although the FDA does allow for UV
blocking labeling. In this regard, a Class 2 contact lens absorbs 70
percent of UVA and 95 percent of UVB (the same as the ANSI standard
for a sunglass lens). A Class 1 contact lens absorbs 90 percent of
UVA and 99 percent of UVB.
manufacturers incorporate UV-absorbing characteristics into their
polymers, and to my knowledge the first hydrogel associated with
this novel technology was the Precision UV lens (now CIBA Vision).
Today, Class 2 materials are manufactured by Vistakon, CooperVision,
CIBA Vision, Dosco and Sauflon. Vistakon manufactures Class 1
lenses are an attractive means of complete internal ocular
protection given the coverage by the lens of the entire cornea and
entrance pupil of the eye. This once again highlights the tremendous
benefits contact lenses afford our patients.