New Page 1
When a Contact Lens Is The Healthier Choice
Learn about recent advances in ultraviolet radiation research and clinical
By Jan P.G. Bergmanson, OD, PhD; James E. Walsh, MSc, PhD; Laura Vrazel Koehler,
BS; Judy Harmey, PhD
Contact lens practitioners should not be shy about stressing the advantages of
the products we prescribe. The contact lens has a number of beneficial
attributes, and too often, we fail to point out these attributes to our
As an example, recent research at the Texas Eye Research and Technology Center (TERTC),
part of the University of Houston College of Optometry, has provided excellent
evidence for the ultraviolet (UV) radiation protection offered by a contact lens
when the lens material is formulated with a UV radiation blocker. What�s more,
research has provided evidence that a thinner cornea, one that has undergone
laser refractive surgery, for example, is a less effective UV filter.
In this article, we will discuss new scientific data on UV radiation and its
First, let�s review why UV protection has become necessary to maintain ocular
health and why it is an especially important consideration for eyecare
Over the years, chemicals released by man, especially chlorofluorocarbons, have
led to thinning of the ozone layer, a natural UV radiation filter. As the ozone
thins, a greater proportion of UVA and UVB radiation can penetrate it. When a
hole develops in the ozone layer, highly toxic UVC radiation has free access to
the earth�s surface. What takes man only a short time to harm in our environment
will take nature many years to fully recover. Scientists have projected a half
century will pass before this occurs, if it ever does.1
There is little doubt UV radiation is one of our most serious and farreaching
health challenges. Today, skin cancer is the most common cancer in the southern
United States.2,3 At the University of Houston College of Optometry,
we assessed ambient UV radiation intensities on the roof of our facility during
two consecutive summers. Our findings revealed that radiation levels were
unhealthy nine days out of 10.4
This man-made environmental change has the potential to increase the incidence
of all UV-related eye diseases unless we become more vigilant in our preventive
care. In rural regions with high UV radiation intensities where, as a result,
the lifetime UV radiation dose is high, pterygia and cataracts are the most
common ophthalmic diseases.5 A careful review of the literature shows
that the only scientifically established risk factor associated with pterygium
formation is UV radiation.
The combined epidemiology of UV-related ocular conditions is quite astounding
when you consider the prevalence of pterygia, which may affect more than 20% of
the population in some places on earth, with cataract statistics not far behind.5
Since this environmental health threat will be around for a very long time, we
should consider changing our prescribing habits.
Inadequate Natural Response
When considering this toxic environment, we must examine human behavior and
society�s awareness of the need to wear ocular UV-radiation protection. When the
eye is exposed to the sun�s direct rays, the natural protection response is to
squint. However, when we�re not directly facing the sun or when there is light
cloud cover, the squint mechanism is reduced. Most people are unaware that up to
40% of ambient UV radiation is contained in the diffuse solar component. In
addition, a laterally incident direct solar beam can be focused onto the nasal
limbus without stimulating the squint mechanism. Not surprisingly, the nasal
limbus is a common site of UV-related ocular diseases, such as pterygium and
Although helpful, UV-filtering sunglasses should not be our sole response to
this ocular hazard because certain styles reduce the natural squint mechanism
while allowing laterally focused UV radiation onto the nasal limbus. A
UV-blocking contact lens will more efficiently reduce UV radiation and will do
so at all times if worn all day, as is the case with most successful contact
lens wearers. Unfortunately, refractive surgery patients, while no longer
requiring contact lenses, may have a reduced natural UV radiation filter, a
Ocular Protection Front and Back
The degree of protection offered by UV-blocking eyewear is not just a function
of their design or the fact that they are placed over the eye. The spectral
nature of the UV blocker they employ is also important. Solar UV radiation can
be subdivided into three distinct wavebands, each with its own unique
� UVC (100-280 nm) is the most toxic waveband, but it is filtered by the ozone
in the earth�s atmosphere, so if the ozone layer is not excessively damaged, UVC
filtering does not have to be considered in eyewear design.
� UVB (280-315 nm) is present at toxic levels on the earth�s surface, and it is
vital that this waveband is fully eliminated by eyewear UV blockers.
� UVA (315-400 nm) used to be considered safe for tanning salons. So safe, in
fact, that it wasn�t considered in the development of skin protection and
tanning lotions. This is no longer true. A good UV-blocking eyewear filter
should eliminate all UVA radiation and possibly some of the blue light region,
which is also thought to have a toxic contribution, especially to retinal
The principal measure of
protection is the UV-visible transmission spectrum and related protection factor
(see Figures 1, 2 and 3). The ideal transmission spectrum has its cutoff
wavelength as close to the visible blue region as possible. The protection
factor is essentially the inverse of the transmission summed up in the waveband
of interest. It is similar to those calculated for skin-related sunblock, but
the requirement is to maximize the value because it is undesirable to have any
ocular UV radiation exposure. The eye cannot see UV radiation so, consequently,
this radiation is useless to vision.
Just as people are aware of the relative protection factors of UV-blocking
sunscreens, they also should be aware of the blocking efficacy of their eyewear,
particularly when they live in tropical or subtropical zones. With most
diseases, protection is the best form of cure, and this is particularly true for
certain UV-related ocular conditions, such as pterygium, for which surgical
excision is the primary treatment and recurrence and complication rates are
In addition to anterior segment protection from UV radiation, in which the
cornea provides very limited natural protection, posterior segment protection
can be enhanced. One option is contact lenses with a UV-cutoff wavelength closer
to the visible blue than the crystalline lens, which is the primary UV-blocking
ocular component. The crystalline lens itself also needs protection to prevent
cataract formation, which is considered a more serious condition than those that
occur on the ocular surface, such as pterygia. The relative importance of
various UV-related ocular conditions is not an issue, however, if efficient
blocking is provided.
The conjunctiva is as easily harmed by UV radiation as the cornea,7
and in UV keratitis, the sandin-the-eyes symptomology results from conjunctival
trauma. As we mentioned previously, the most well-established UV-related
conjunctival disease is the pterygium, for which the only scientifically known
risk factor is UV radiation. This anomaly becomes more prevalent among people
who live closer to the equator. In the southern United States, it may affect
more than 10% of the population, 8 and in some high altitude areas of
central Mexico, more than 20% will have pterygia.5 This high
incidence makes it by far the most common ophthalmic disease.
In most people, a pterygium is a cosmetic problem that can affect quality of
life. However, it can grow over the limbus and into the cornea, affecting
vision, first by inducing astigmatism, ultimately covering the visual axis, and
causing blindness. Surgery to remove a pterygium is not an easy procedure.
Complications and recurrence rates are unacceptably high.
Pterygia manifest most often on the nasal side of the limbus along the
horizontal meridian. The current theory on the etiology of the pterygium
suggests that temporally and tangentially incident rays are focused by the
cornea on the opposite side at the limbus. It has been calculated that this
corneal focusing ability can concentrate light by a factor of 20. Coroneo and
colleagues9 were first to propose this optical effect; and
researchers at the TERTC have demonstrated this phenomenon in vivo.10
The effect of UV radiation focused in this manner is to harm vital stem cells in
this region. The irradiated stem cells will mutate in the p53 gene, which
initiates a cascade of events leading to pterygium growth. The goal of our
research is to map the series of changes from the mutation among epithelial
cells leading to the growth of mature pterygium, which shares many
characteristics of a precancerous growth. Once we�ve achieved a more complete
understanding of pterygium formation, we will be better equipped to search for
ways to stop its advancement and eventually develop a nonsurgical method of
treatment. Currently, prevention remains our best strategy.
The UV-blocking soft contact lens is uniquely able to protect the limbal and
conjunctival stem cells by covering the regions populated by these cells. Thus,
people who wear UV-blocking contact lenses all day are protected from sunup to
sundown, while nonlens wearers typically do not wear sunglasses all day. What�s
more, most sunglasses will not protect wearers from the tangentially incident
rays, although wraparound sunglasses would offer some protection against
peripherally incident radiation. Spectacles have the same limitations as
Although the literature suggests a connection with UV radiation, pingueculae
have not been studied extensively and specifically for a UV radiation origin.
Interestingly, pingueculae show the same predilection for a nasal presentation
UV-related corneal complications are well-documented. The association between
snowblindness and photokeratitis/UV keratitis was uncovered by the Swedish
ophthalmologist E.J. Widmark more than 100 years ago.
UV keratitis is an acute response to an abovethreshold dose, which leads to
epithelial cell death but spares the nerve fibers.11 The survival of
the nerve fibers leads to the significant pain associated with this condition.
Cell death may be observed clinically as an area of distinct staining within the
palpebral fissure. Erythema of the eyelids and face may be present as well, and
a broad-spectrum, topical, prophylactic antibiotic should be prescribed.
Irrigation and patching of the eye also may be indicated, but if the patient
wears non-UV-blocking contact lenses, patching is contraindicated.
Chronic exposure of the cornea to UV radiation leads to climatic droplet
degeneration, which characteristically manifests within the palpebral aperture
and affects people who spend considerable time outdoors. This condition may also
be seen in the conjunctiva and may occur together with pterygium and pinguecula.
Histopathologically, spheroids are located in the stroma and also involve the
epithelium. Their content is proteinacious, but the precise composition is not
Literature has shown that the endothelium, which cannot regenerate, is
vulnerable to UV radiation. Laboratory experiments have demonstrated the
toxicity of UV radiation to the endothelium, and clinical observations have
established polymegethism and corneal edema as part of the endothelial response
to UV radiation.12-16
Recent research at the TERTC demonstrated that significant corneal UV radiation
absorption takes place within the stroma. Previously, it was thought that most,
if not all, corneal UV radiation absorption occurs in the epithelium.17
This notion probably stems from the fact that in photokeratitis, or
snowblindness, there is a clinically obvious loss of epithelial cells, and there
is full recovery with no obvious permanent loss of transparency. Since the
corneal stroma is an important UV radiation absorber, it follows that thinning
of this tissue will have a negative impact on the cornea�s ability to keep such
radiation out of the eye. Conditions that lead to stromal thinning include
keratoconus and pellucid marginal degeneration. In these cases, it may be
beneficial to prescribe a UV radiation filter, preferably formulated in the
matrix of a contact lens.
Perhaps more important, considering the number of patients affected, are
individuals who have had LASIK, PRK or PTK. These patients have thinner stromas
because the laser removes stromal tissue. These corneas will allow more and
shorter UV radiation wavelengths through to the crystalline lens, thus
increasing the risk for early cataract development. However, it will take years
before we have the clinical data on the incidence of cataracts for patients who
had excimer laser surgery. Some may argue that the burden of proof on this issue
lies with the laser manufacturers and possibly the surgeons performing these
procedures. We have not proven that excimer laser patients will develop
cataracts at an earlier age. This is, however, a realistic concern, and we think
it is prudent to advise our refractive surgery and PTK patients about the
potential increased risk. We should also advise them about UV radiation
Research into the risks of refractive surgery presents an outstanding
opportunity for contact lens practitioners to promote some of the virtues of
contact lenses. These devices actually protect the eye from UV radiation and
potentially prevent early cataracts and other UV-related diseases. In contrast,
excimer laser surgery renders a patient more vulnerable to complications caused
The crystalline lens is the principal ocular UV radiation filter, and
above-threshold UV radiation causes this tissue to lose its transparency, a
condition we all know as cataract. If we live long enough, we all will get
cataracts. It follows that the primary risk factor for cataract is age, but
several other risk factors are worth mentioning. These include UV radiation,
diabetes, certain medications, smoking and being female.18,19,20
It makes good sense to reduce the burden on the crystalline lens by minimizing
exposure to the factors we can control, including UV radiation. The cortical
cataract is the type most associated with UV radiation.21 Delaying cataract
surgery is not only a personal decision but also a public health issue of
It has been projected that the ozone will deplete by as much as another 20% over
the next 10 or 20 years, which would lead to an increase of cortical cataracts
by 1.3% to 6.9%. This increase amounts to an additional 167,000 to 830,000
cases, at an estimated cost to society of $563 million to $2.8 billion.22
Add to this public health challenge the potential for early cataracts to occur
in excimer laser patients, and we have a huge expense to cover in the
The retina and the vitreous chamber are predominantly protected from UV
radiation by the blocking power of the crystalline lens, which cuts off the high
UVA beyond the cutoff wavelength of any currently available contact lens.
However, because UV transmission through the crystalline lens is higher in the
younger eye and because this population tends to expose itself to more UV
radiation, it may be prudent to provide additional protection beyond that
afforded by the crystalline lens. The requirements for a UVblocking contact lens
that could achieve this would include a cutoff wavelength as close to or even
into the visible blue region. This kind of prophylactic lens would provide
nearly complete protection from the cornea to the retina.
The retina is easily harmed by UV radiation but, as mentioned, the crystalline
lens normally provides protection. However, in the aphakic eye, this protection
must be provided by other means. Typically, the implanted intraocular lens will
offer protection, but in cases where the patient has not been given one, we must
ensure that the retina is not exposed to UV radiation without adequate
protection. A UV-blocking contact lens is the ideal solution for these patients.
Thwart the Threat
In our opinion, we are underselling the contact lens as a UV radiation filter.
The most recent UVblocking contact lenses provide as good or better UV radiation
protection than spectacle lenses. In the successful wearer, the lenses are on
the eye all day and cover the vital limbal and conjunctival stem cells, which
are essential to corneal health. Our research has shown that even in some of the
most UV radiation-intense climates, the UV-blocking contact lens reduces
exposure to safe levels.5
UV radiation causes cataract and is a threat to corneal and conjunctival health.
Unfortunately, current literature and scientific and continuing education
meetings are a poor reflection of this fact. Instead, it seems there is a
preoccupation with grade 1 and 2 corneal staining and ocular redness, and
matters relating to comfort. These are important performance measures for
contact lenses, but they are hardly serious ocular health concerns. The industry
may wish to advertise any advantages products have, but in clinical practice, we
must not lose sight of the bigger picture. Stem cell damage, cataracts, pterygia
and climatic droplet keratopathy are serious ocular health considerations that
should not be ignored or overshadowed by lesser concerns.
1. Madronich S, McKenzie RL, Bjorn LO, Caldwell MM. Changes in biologically
active ultraviolet radiation reaching the Earth�s surface. J Photochem and
Photobiol B. 1998;46: 5-19.
2. Scotto J, Fears TR, Fraumeni JF. Incidence of nonmelanoma skin cancer in the
United States. NCI NIH Publ. No. 83-2433, 1983.
3. Scotto J. Risk Factors: Solar radiation, in Harras A. (ed): Cancer Rates and
Risks, (ed. 4). NCI NIH Publ. No. 96-691. May 1996.
4. Walsh JE, Bergmanson JPG, Saldana G, Gaume A. Can UV radiation-blocking soft
contact lenses attenuate UV radiation to safe levels during summer months in the
southern United States? Eye Contact Lens. 2003;29:S174-S179.
5. Horner DG, Long A, Roseland J, et al. Pterygia, cataract, and age-related
macular degeneration in a Hispanic population. Optom & Vis Sci. 2006;83(Supp).
6. Walsh JE, Koehler LV, Flemming DP, Bergmanson JPG. Novel method for
determining hydrogel and silicone contact lens transmission curves and their
spatially specific ultraviolet radiation protection factor. Accepted for
publication in Eye & Contact Lens, August 2006.
7. Cullen AP, Perera SC: Sunlight and human conjunctival action spectrum.
Ultraviolet radiation hazards, SPIE Proceedings. 1994;2134:24-30.
8. Taylor HR. A Historic perspective of pterygium. In Tayor HR, ed. Pterygium.
Kugler Publications. The Hague, The Netherlands. 2000; 3-13.
9. Coroneo MT, Muller-Stolzenburg NW, Ho A. Peripheral light focusing by the
anterior eye and the ophthalmohelioses. Ophthalmic Surg. 1991;22:705-711.
10. Walsh JE, Bergmanson JPG, Wallace D, et al. Quantification of the
ultraviolet radiation (UVR) field in the human eye in vivo using novel
instrumentationand the potential benefits of UVR blocking hydrogel contact
lenses. Br J Ophthalmol. 2001;85;1080-1085.
11. Bergmanson JPG. Corneal damage in photokeratitis: why is it so painful?
Optom Vis Sci. 1990;67:407-413.
12. Ringvold A, Davanger M, Olsen EG. Changes of the cornea endothelium after
ultraviolet radiation. Acta Ophthalmol.1982;60:41-53.
13. Karai I, Matsumura S, Takise S, et al. Morphological change in the corneal
endothelium due to ultraviolet radiation in welders. Br J Ophthalmol.
14. Pitts DG, Bergmanson JPG, Chu LW. Ultrastructural analysis of corneal
exposure to UV radiation. Acta Ophthalmol.1987;65:263-273.
15. Good GW, Schoessler JP. Chronic solar radiation exposure and endothelial
polymegethism. Curr Eye Res. 1988;7:157-162.
16. Clarke SM, Doughty MJ, Cullen AP. Acute effects of ultraviolet-B irradiation
on the corneal surface of the pigmented rabbit studied by quantitative scanning
electron microscopy. Acta Ophthalmol.1990;68:639-650.
17. Kinsey E. Spectral transmission of the eye to ultraviolet radiations. Arch
18. Mukesh BN, Le A, Dimitrov PN, et al. Development of cataract and associated
risk factors: the Visual Impairment Project. Arch Ophthalmol. 2006;124:79-85.
19. West SK, Duncan DD, Munoz B, et al. Sunlight exposure and risk of lens
opacities in a population-based study: The Salisbury Eye Evaluation Project.
20. Carlsson B, Sjostrand J. Increased incidence of cataract extractions in
women over 70 years of age. A population based study. Acta Ophthalmol Scand.
21. Taylor HR, West SK, Rosenthal FS, et al. Effect of ultraviolet radiation on
cataract formation. New Engl J Med. 1988;319:1429-1433.
22. West SK, Longstreth JD, Munoz BE, et al. Model of risk of cortical cataract
in the US population with exposure to increased ultraviolet radiation due to
stratospheric ozone depletion. Am J Epidemiol. 2005;162:1080-1088.
Contact Lens Spectrum, Issue: May 2007