The UV Spectrum
Ultraviolet radiation (UVR) occurs in the invisible light spectrum of 100 nm to 400 nm and is divided into three bands, UVA, UVB and UVC, based on biologic effects.1
TYPES OF UVR
In order to understand the damage UVR can have on the eye, it is helpful to relate the types of UVR to the different kinds of damage it can cause and to look at the effects of UVR on the cellular and the ocular levels.
- UVA is responsible for skin tanning and ageing
- UVA rays are between 315 nm and 400 nm in wavelength2
- 95% of solar UV energy reaching the equator is UVA2
- UVA has been shown to exacerbate the ocular damage caused by UVB3
- UVB damages DNA and causes tissue damage and sunburn
- UVB rays are between 280 nm and 315 nm in wavelength2
- UVB accounts for 5% of solar UV energy reaching the equator2
- UVB is much more biologically active than UVA4
- UVC is the most toxic waveband, but most of it is absorbed by the atmosphere
- UVC rays are between 100 nm and 280 nm in wavelength2
- UVC is germicidal
UV: SOURCES, RISKS AND HOW CONTACT LENSES CAN HELP
Download a patient version of this animation for use in your practice (92Mb, .wmv format)
Should we be advising our patients about the need for ocular protection?
Professor James Wolffsohn reviews the latest evidence to help us understand the need to raise awareness of UV exposure on the eye and advise options for protection. Download article
UV radiation and the eye
Karen Walsh reviews UV-induced ocular pathology, the challenges of providing adequate ocular protection and the role of UV-blocking soft contact lenses. Download article
1. Parrish JA, Anderson RR, Urbach F, et al. UV-A: Biological Effects of Ultraviolet Radiation with Emphasis on Human Responses to Longwave Ultraviolet. New York, NY: Plenum Press; 1978: chap 1.
2. Ultraviolet (UV) Radiation, Broad Spectrum and UVA, UVB, and UVC. Updated May 25, 2005. Accessed December 5, 2007.
3. Sheedy J, Edlich RF. Ultraviolet eye radiation: the problem and solutions. J Long Term Eff Med Implants. 2004;14(1):67–71.
4. Fishman GA. Ocular phototoxicity: guidelines for selecting sunglasses. Surv Ophthalmol.1986:31:119–24.
How does radiant UV energy damage cells and tissues?
Radiant UV energy is readily absorbed by nucleic acids, proteins, lipids and other molecules within cells.1Most of this energy dissipates, but the remainder can structurally alter molecules. In turn, a damaged molecule may react with other molecules within the cell.2 Some specific cellular consequences of UV exposure that have been documented include point mutations of DNA,3–4, protein denaturation and cell death.3,6,7
1. Molho-Pessach V, Lotem M. Ultraviolet radiation and cutaneous carcinogenesis. Curr Probl Dermatol. 2007;35:14–27.
2. Taylor HR. Ultraviolet radiation and the eye: an epidemiologic study. Tr Am Ophth Soc. 1989;87:802–53.
3. Rünger TM. How different wavelengths of the ultraviolet spectrum contribute to skin carcinogenesis: the role of cellular damage responses. J Invest Dermatol. 2007;127(9):2236-44.
4. Allan J. Ultraviolet radiation: how it affects life on earth. Published September 6, 2001. Accessed December 5, 2007.
5. Mutations: what they are, their causes and effects – an overview. Updated November 27, 2007. Accessed December 6, 2007.
6. Berneburg M, Gattermann N, Stege H, Grewe M, Vogelsang K, Ruzika T, et al. J. Chronically ultraviolet-exposed human skin shows a higher mutation frequency of mitochondrial DNA as compared to unexposed skin and the hematopoietic system. Photochem Photobiol. 1997;66(2):271-5.
7. Apoptosis. Published November 30, 2007.Accessed December 6, 2007.
UVR damage is cumulative and permanent. It can affect the cornea, lens, iris, retina and related epithelial and conjunctival tissues. Damage to four critical structures – the conjunctiva, cornea, lens and retina – is well documented.1
The conjunctiva is easily damaged by UVR. UVR activates a complex series of oxidative reactions and distinct pathways of cell death.2
Both the epithelium and the endothelium (which cannot regenerate) are vulnerable. Increased UVB exposure causes substantial damage to the corneal antioxidant protective mechanism, resulting in injury to the cornea and other parts of the eye.3
A significant amount of UVR is absorbed by corneal stroma. Thinning of this tissue due to keratoconus or refractive surgery allows more UVR to reach the lens. Because refractive surgery is a fairly new procedure, it will be many years before we know whether surgical thinning of the stroma increases the risk of earlier cataract development.4
Over time, the lens yellows and loses its transparency, primarily due to irreversible lens protein changes5caused by aging, heredity and UV exposure.6
The retina is generally protected from UVR by the filtering power of the lens. However, because more UVR is transmitted through younger, clearer lenses, ocular protection from UV exposure is even more critical for children
Research: the ocular surface reflects UVR onto the side of the nose
Australian researchers have found that the incidence of basal cell carcinoma was significantly higher on the side of the nose than other parts of the face exposed to direct sun exposure. By using a model that simulated light rays reflecting off the curved surface of the eye from a range of angles, the scientists discovered that the curved shape of the eye created a focussing effect, producing UV hot spots on the side of the nose. Lead investigator Dr. Benjame Birt concluded, "Good wrap-around sunglasses reduce the amount of UV radiation reaching the eyes from all angles".7
1. Sliney DH. How light reaches the eye and its components. Int J Toxicol. 2002;21(6):501–9.
2. Buron N, Micheau O, Cathelin E, Lafontaine PO, Creuzot-Garcher C, Solary E. Differential mechanisms of conjunctival cell death induction by ultraviolet irradiation and benzalkonium chloride. Inv Ophthalmol Vis Sci. 2006;47(10):4221–30.
3. Cejkova J, Stipek S, Crkovska J, Ardan T, Platenik J, Cejka C, Midelfart A. UV rays, the prooxidant/antioxidant imbalance in the cornea and oxidative eye damage. Physiol Res. 2004;53:1–10.
4. Cohen S. SOS: ultraviolet radiation and the eye. Rev Cornea Contact Lens. October 2007:28–33.
5. Taylor LM, Aquilina J, Jamie JF, Truscott RJ. UV filter instability: consequences for the human lens. Exp Eye Res. 2002;75(2):165–75.
6. Robman L, Taylor H. External factors in the development of the cataract. Eye. 2005;19(10):1074–82.
7. Birt B, Cowling I, Coyne S, Michael G. The effect of the eye's surface topography on the total irradiance of ultraviolet radiation on the inner canthus. J Photochem Photobiol B. 2007;87(2)27–36.