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.1 Most 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 changes5 caused 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.
UV-related eye conditions
UV exposure has been implicated as a risk factor or cause in the pathogenesis of a large number of ocular conditions.1-4 These ocular conditions include pinguecula, pterygium, UV keratoconjunctivitis, cataract, macular degeneration, squamous cell carcinoma, ocular melanoma and climatic droplet keratopathy. Read more about some of the most common UV-related eye conditions:
UV exposure appears to be the most significant factor in the development of pterygium.8-11 There is a higher incidence in people who live near the equator and is seen from 20s and 30s in high environments or activities (eg surfers, sailors, fishermen). It is related to UV exposure in youth and dry, windy climates.12 Vision can be affected.
- The conjunctival stroma degenerates and is replaced by thick fibres. The corneal stroma also can be affected. In the case shown here, it appears the pterygium is just beginning to encroach on the cornea of the left eye
- The pterygium is typically a raised, wing-shaped patch of fibrous, fibrovascular or vascular tissue. It is also commonly nasal in location
- Patients are often asymptomatic, but may come to you because they are concerned about appearance
- Pterygium is difficult to treat; surgery is not always successful
Acute overexposure to the sun can result in photokeratitis (UV keratoconjunctivitis).13
UV keratoconjunctivitis progresses as follows:
Cataract2,14,15 is the leading cause of blindness in the world. In many societies, cataract removal is one of the most commonly performed surgical procedures. It begins in 40s-50s and symptoms include blurred vision, haloes and glare with night driving.
Cataract development is very complex
- Age and heredity are the most important risk factors for the development of all types of cataracts
- UV exposure is considered a major risk factor for cataract development and has been linked to early onset of cortical cataract.14 Although the correlation between UV and cortical cataract has experimentally been well established, the exact role of UV exposure in the natural development of the condition is not well understood
- Other risk factors include smoking, diet, medication and general health
Ways in which UV exposure can affect the lens and potentially induce cataract: some postulated mechanisms
- Changes to photosensitive amino acids in lens proteins
- Covalent binding of UV filter compounds to lens proteins
- Formation of reactive toxic oxidants
- Direct damage of DNA within corneal epithelium
1. Coroneo M. Sun, eye, the ophthalmohelioses and the contact lens. Eye Health Advisor, a magazine of Johnson & Johnson Vision Care, January 2006.
2. Young RW. The family of sunlight-related eye diseases. Optom Vis Sci. 1994;71(2):125–44.
3. Taylor HR, West S, Munoz B, Rosenthal FS, Bressler SB, Bressler NM. The long-term effects of visible light on the eye. Arch Ophthalmol. 1992;110(1):99–104.
4. Wittenberg S. Solar radiation and the eye: a review of knowledge relevant to eye care. Am J Optom Physiol Opt. 1986;63(8):676–89.
5. Perkins ES. The association between pinguecula, sunlight and cataract. Ophthalmic Res. 1985;17(6):325–30.
6. Lica L. Pinguecula and pterygium. Gale Encyclopedia of Medicine website, accessed via BNET Research Center Web site. Published 1999. Accessed December 7, 2007.
7. Ooi J-L et al. Ultraviolet fluorescence photography to detect early sun damage in the eyes of school-aged children. Amer J Ophthalmol 2006; 14(2): 294-298.
8. Saw SM, Tan D. Pterygium: prevalence, demography and risk factors. Ophthalmic Epidemiol. 1999;6(3):219–28.
9. Ang LP, Chua JL, Tan DT. Current concepts and techniques in pterygium treatment. Curr Opin Ophthalmol. 2007;18(4):308–13.
10. Mackenzie FD, Hirst LW, Battistutta D, Green A. Risk analysis in the development of pterygia. Ophthalmology. 1992;99(7):1056–61.
11. Nolan TM, DiGirolamo N, Sachdev NH, Hampartzoumian T, Coroneo MT, Wakefield D. The role of ultraviolet irradiation and heparin-binding epidermal growth factor-like growth factor in the pathogenesis of pterygium. Am J Pathol. 2003;162:567–74.
12. McCarty et al. Epidemiology of pterygium in Victoria, Australia. Brit J Ophthalmol 2000; 84(3): 289-292.
13. Bergmanson JP. Corneal damage in photokeratitis—why is it so painful? Optom Vis Sci. 1990;67(6):407–13.
14. McCarty CA, Nanjan MB, Taylor HR. Attributable risk estimates for cataract to prioritise medical and public health action. Invest Ophthalmol Vis Sci. 2000;41(12):3720-5.
15. Ellwein LB, Urato CJ. Use of eye care and associated charges among the Medicare population. Arch Ophthalmol. 2002;120(6):804-11.
16. Bialek-Szymanska A, Misiuk-Hojlo M, Witkowska D. Risk factor evaluation in age-related macular degeneration. Klin Oczna. 2007;109(4–6):127–30.
17. Loeffler KU, Sastry SM, McLean IW. Is age-related macular degeneration associated with pinguecula or scleral plaque formation? Curr Eye Res. 2001;23(1):33–7.
18. Cruickshanks KJ, Klein R, Klein BE, Nondahl DM. Sunlight and the 5-year incidence of early age-related maculopathy: the Beaver Dam Eye Study. Arch Ophthalmol. 2001;119(2):246–50.
19. Taylor HR, Munoz B, West S, Bressler NM, Bressler NM, Bressler SB, Rosenthal FS. Visible light and risk of age-related macular degeneration. Trans Am Ophthalmol Soc. 1990;88:163–73; discussion 173–8.
20. Chalam KV, Khetpal V, Rusovici R et al. A review: role of ultraviolet radiation in age-related macular degeneration. Eye & Contact Lens 2011; 37(4): 225-232.
21. Wagner R S. Why children must wear sunglasses. Contemp Pediatr, 1995, 12: 27-31.