Article

CONTACT LENS DESIGN & MATERIALS

ULTRAVIOLET-PROTECTIVE CONTACT LENSES

It should be our top priority to reduce the amount of ultraviolet (UV) energy to which our patients are exposed, because UV energy can cause significant eye damage (Chandler, 2011). UV energy may induce acute ocular irritation or solar keratopathy, or it could produce cumulative damage that can result in cortical cataracts, pinguecula, climatic droplet keratopathy, macular degeneration, or even cancer (Chandler, 2011; Rahmani et al, 2014; Artigas et al, 2016).

UV damage directly (e.g., apoptosis activation) or indirectly (e.g., free-radical generation) causes pathology by inducing protein cross-linking, altering enzyme activity, damaging cell membranes, or causing genetic mutations (Chandler, 2011). Because the significance of ocular UV damage is underappreciated by patients (Chandler 2011), I would like use this article to highlight some key facts associated with UV energy and how contact lenses (CL) can be used to protect against UV damage.

Ultraviolet Radiation

UV energy affecting the eye primarily emerges from the sun, though some artificial light sources, such as xenon lights, can also produce harmful UV energy (Artigas et al, 2016). The UV energy region of the electromagnetic spectrum can be further broken down into UV-C (200nm to 290nm), UV-B (290nm to 320nm), and UV-A (320nm to 400nm) radiation (Chandler, 2011). The Earth’s atmosphere blocks most of the most harmful (UV-B and UV-C) rays, but some UV-B and most UV-A rays reach the Earth’s surface (Chandler, 2011).

Under normal conditions, the eyebrows and eyelids naturally shield the eye from all but ~5% of ambient UV rays (Chandler, 2011). Of the rays that do reach the eye, the majority of the UV-A rays are absorbed by the crystalline lens, while the majority of the UV-B rays are absorbed by the the cornea and conjunctiva (Osuagwu et al, 2014).

UV-Protecting Contact Lenses

Ocular protection from UV rays should start with UV-blocking sunglasses and hats. If a patient is a CL wearer, UV-protective CLs could provide additional protection (Chandler, 2011). The U.S. Food and Drug Administration (FDA) classifies UV-protecting CLs as Class 1, which are required to block 90% of UV-A and 99% of UV-B rays, or Class 2, which are required to block 70% of UV-A and 95% of UV-B rays (Chandler, 2011). This is in contrast to non-UV-protective CLs, which have been estimated to block about 10% of UV-A and 30% of UV-B rays (Chandler, 2011).

UV-protecting CLs derive their protective properties from UV-absorbing monomers from within the lens matrix (Lira et al, 2009). A CL’s ability to block UV rays can be positively or negatively affected by biofilms that develop during lens wear (Lira et al, 2009); this ability may also increase with greater intensity of colored lens tints (Lira et al, 2009).

Conclusion

Startlingly, less than half of adults wear protective eyewear while spending extended time in the sun, so we need to make a better effort to educate our patients that they should be wearing large hats and/or sunglasses while venturing outside, no matter the time of year (Chandler, 2011). Unfortunately, these measures may still not be enough to protect our patients’ eyes from UV exposure, because UV rays can still make it past these preventative measures. Furthermore, these measures may actually prevent the body’s natural protective reflexes against the sun such as squinting and pupil constriction (Chandler, 2011).

UV-blocking CLs have scientifically demonstrated an ability to reduce corneal and crystalline lens damage (Artigas et al, 2016); therefore, when prescribing CLs to high-risk patients—such as children who spend a lot of time outdoors—I urge you to consider prescribing CLs that have UV-blocking capabilities (Chandler, 2011). CLS

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