Sunlight exposure may be linked to AMD
Study shows late AMD patients have more facial wrinkling than control patients without AMD.
Lifetime exposure to sunlight, as measured by facial wrinkle length, appears to be associated with the development of age-related macular degeneration, according to the findings of a study.
“Chronic inflammation is an important factor [in AMD],” Taiji Sakamoto, MD, told Ocular Surgery News in an e-mail interview. “If mild but chronic damage is caused in the macula by sunlight exposure, it can induce chronic inflammation.”
“Additionally, UV irradiation (sunlight exposure) initiates photochemical generation of reactive oxygen species,” Dr. Sakamoto said. “It increases matrix metalloproteinases and collagen degradation, which is the important process of angiogenesis.”
“If this phenomenon occurs repeatedly, it would affect the eye in a cumulative way,” he said. “Therefore, we have to take lifetime sunlight exposure as a possible cause of AMD more seriously.”
Dr. Sakamoto and colleagues evaluated the association between AMD and sunlight exposure in 148 Japanese men with AMD and 67 Japanese male controls. The AMD patients were grouped according to disease stage: 75 had early AMD and 73 had late AMD.
All patients were 50 years of age or older. The controls averaged 63.1 years of age, while the early and late AMD groups averaged 68.7 years and 72.7 years, respectively. The authors noted that both AMD groups were significantly older than the control group.
Patients presented at either Kagoshima University Hospital or Kagoshima Kouseiren Hospital Health Care Center between May 2005 and February 2006. All had lived in Kagoshima throughout their lives, according to the study.
Measuring sunlight exposure
“Recently, there have been several reports of population-based studies showing sunlight exposure is not a risk factor for AMD,” Dr. Sakamoto said. “Furthermore, there is a trend to say that genetics is the solely major factor for AMD.”
The researchers noted that earlier studies evaluating sunlight exposure used questionnaires, thus relying on participant response.
“There was no objective method to measure the lifetime sun exposure,” Dr. Sakamoto said.
The authors wanted to use a more objective measure to show that there is a connection between sunlight exposure and AMD. They chose to analyze facial wrinkling and hyperpigmentation using the Beauty Imaging System (Procter & Gamble).
“This machine can quantify the length of facial wrinkles and the total size of hyperpigmentation spot of the area of interest automatically,” Dr. Sakamoto said.
“In dermatology, it has been widely accepted that lifetime sun exposure is strongly correlated to facial wrinkles and skin pigmentation,” he said. Additionally, the investigators had conducted earlier studies comparing facial wrinkles and skin pigmentation among Japanese populations living in different areas of the country.
“We found a significant correlation between these factors and where subjects lived,” Dr. Sakamoto said. “These results indicated that facial wrinkles and skin pigmentation could be biomarkers of lifetime sunlight exposure.”
The investigators measured facial wrinkling in a predetermined region of the patients’ upper cheeks. Fine lines longer than 5 mm and wider than 0.16 mm were quantified. In terms of hyperpigmentation, the investigators observed spots on the left and right sides of participants’ faces and used the average of the two spot counts for comparison.
After assessing facial wrinkle length and hyperpigmentation, the authors also evaluated the tone of each participant’s skin on the upper inner arm using the CR-13 color reader (Minolta), according to the study.
Patients with late AMD had more facial wrinkles than controls (P = .047); however, early AMD patients did not have significantly more facial wrinkles than controls, the authors found.
In contrast, late AMD patients had less areas of hyperpigmentation than controls (P = .035), and there was no difference in hyperpigmentation between early AMD patients and controls, according to the study.
“Late [AMD] cases had a significantly less hyperpigmentated spot area fraction, despite the fact that our previous report concluded that hyperpigmentation was also increased by lifetime sun exposure,” Dr. Sakamoto said. This may suggest that the skin of patients with AMD reacts differently to sunlight exposure than that of patients without AMD, regardless of the actual amount of exposure.
“It may be that sunlight/UV irradiation induces changes in skin pigmentation, but the biological pathway differs from that of wrinkle formation,” the authors said in the study.
Overall, AMD patients had “darker, redder and more yellow skin” than controls, but there was no significant difference in skin tones between AMD patients and controls, they said.
“It is too early to make a final conclusion” regarding the connection between sunlight exposure and AMD, Dr. Sakamoto said. However, he noted that sunlight exposure is still an important consideration in evaluating the potential external causes of AMD.
“Although this is a pilot study, it should be remembered that there might be environmental factors which affect AMD progression,” he said. “Sunlight exposure is still one of the candidates. Even though it is not proven to be the one conclusively, people should not be exposed to sunlight needlessly.”
Therefore, for those who inevitably spend large amounts of time in the sun, Dr. Sakamoto recommended sunglasses.
“Supplementation with antioxidants might be beneficial, especially for those who are habitually exposed to sunlight (eg, farmers or fishermen) because sunlight exposure would induce free radicals in the eye,” he said.
For more information:
- Taiji Sakamoto, MD, can be reached at the Department of Ophthalmology, Kagoshima University Graduate School of Medical and Dental Sciences, 8-35-1 Sakuragaoka, Kagoshima 890-8520, Japan; e-mail: firstname.lastname@example.org.
- Hirakawa M, Tanaka M, Tanaka Y. Age-related maculopathy and sunlight exposure evaluated by objective measurement. Br J Ophthalmol. 2008;92:630-634.
- Jessica Loughery is an OSN Correspondent who is based in Philadelphia.