Working to Prevent Age-Related Macular Degeneration — Part 2
BY LEO SEMES, OD, FAAO
In my last column on age-related macular degeneration (AMD) prevention, I cited the U.S. surgeon general's statement regarding a prescription for overall health. The discussion centered on lifestyle choices. Here I'll discuss another aspect of the report and AMD: guided preventive measures.
A Brief UV Review
We know that the full spectrum of sunlight does not normally reach the earth's surface. The highly energetic UV-C rays are absorbed by the earth's ozone layer, and except for specific gaps, do not represent a hazard at present. UV-B and UV-A along with the visible spectrum, however, have the potential to be absorbed by skin and eyes. The cornea and lens absorb most of the UV rays, which in acute situations can lead to corneal toxicity and premature cortical cataract formation. The biggest risk to the retina is from the visible spectrum. The most damaging portion is the shortwavelength end or blue light.
The mechanism of damage seems to be oxidation and consequent damage to the retinal pigment epithelium and photoreceptors. Clinical manifestations are drusen and pigmentary disruptions. These two observations form the basis for assessing and assigning risk for development of vision loss (Ferris et al, 2005).
Prevention and Treatment
Once we determine that a patient is at risk for AMD, we can recommend diet changes and dietary supplements. But what about preventive measures for those who are too young to show clinical changes or for those who may be at risk due to family history, occupational exposure, or other risks, for example?
This warrants recommending comprehensive sun protection. Consider recommending UV-radiation/ blue-light attenuating lenses. Looking at spectra from lenses will help determine adequate protection. A variety of lenses will meet criteria for UV-A and B protection and should be incorporated into all spectacle lenses, regardless of patient age. The fact that UV damage is cumulative over a lifetime and that most environmental UV exposure is encountered early in life supports this recommendation.
The same is true for blue-light exposure. Blue light is more likely to reach the retina, and this mechanism continues to emerge as the culprit in DNA damage that manifests itself as AMD.
While genetic determinants undoubtedly play a role, mitigating damage for those at risk represents a significant step forward in the battle against AMD.
When we encounter patients who have clinical manifestations of early AMD, we have a number of options. Dietary supplements and environmental UV and bluelight attenuation should be at the top of the list. In addition, AMD patients who require our low-vision services are often accompanied by a family member. We should take the opportunity to recommend protective strategies for these individuals, for example.
Other opportunities to minimize the impact of AMD include sun protection recommendations for those with significant occupational or recreational exposures. Remember that UV exposure increases by 5 percent for each 1,000 feet of altitude above sea level. So skiers, for example, and others playing or living and working at this altitude would fall into this category. The same is true for latitudes closer to the poles.
Taking the Lead on Prevention
Eyecare practitioners can establish themselves as prevention professionals with knowledgeable recommendations. We have the potential to make meaningful differences in patients' lives. CLS
For references, please visit www.clspectrum.com/references.asp and click on document #180.
Dr. Semes is a professor of optometry at the UAB School of Optometry.