日光暴露、近視予防に効果

・日光に含まれる紫外線には白内障のリスクを上げる。

・紫外線で皮膚癌が増える。

・紫外線でVitaminDの合成が促進される。

・日光が眼軸長の延長を抑制する。

適度な日光を浴びることは必要ですが、過度の紫外線は弊害があります。

眼軸長を延長させないような日光の成分を透過させ、紫外線を大幅にカットするサングラス等が開発されることが望ましいのかも知れません。

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台湾とデンマークで学童対象に調査

2013年5月10日 米国学会短信

　米国眼科学会（AAO）は5月1日、屋外活動や日照時間が小児の近視に好影響を及ぼすと示した2件の研究を紹介した。Ophthalmology 5月号に掲載している。

　台湾で行われた1件の研究では、ある小学校の児童333人を休み時間に屋外で過ごさせ（1日当たり80分間）、近隣の小学校の児童を対照群とし、休み時間に屋外で過ごす義務を課さなかった。研究開始時と1年後に視力を検査して両群を比較したところ、屋外で過ごした児童では近視または視力低下が有意に減少した。

　またデンマークで行われた別の研究では、近視の学童235人を季節ごとに7群に分け、それぞれの季節区分の始めと終わりに眼軸長（眼軸長が延長すると近視が悪化）と視力を測定した。デンマークでは季節ごとの日照時間の差が大きい（夏18時間、冬7時間）が、日照時間が最短の時期での眼軸長の延長は平均0.19 mmだったのに対し、最長の時期では平均0.12 mmだった。

　それぞれの研究を行った研究者はこれらの結果から、学童の近視予防には学校単位での取り組みが望ましいとし、児童が屋外で過ごすよう指導する、あるいは必要に応じて昼光スペクトル灯などを使用することを保護者や教育関係者に勧めている。

Evidence Mounts That Outdoor Recess Time Can Reduce the Risk of Nearsightedness in Children

05/01/2013 08:30:00 AM

Two studies provide new data on impact of daylight exposure on eye development

SAN FRANCISCO—Two new studies add to the growing evidence that spending time outdoors may help prevent or minimize nearsightedness in children. A study conducted in Taiwan, which is the first to use an educational policy as a public vision health intervention, finds that when children are required to spend recess time outdoors, their risk of nearsightedness is reduced. A separate study in Danish children is the first to show a direct correlation between seasonal fluctuations in daylight, eye growth and the rate of nearsightedness progression. The research was published in the May issue of Ophthalmology, the journal of the American Academy of Ophthalmology.

Nearsightedness in childhood is correctable, but is also linked to development of severe forms of this eye disorder in adulthood, which increases risks for potentially blinding diseases such as glaucoma and retinal detachment.Research on nearsightedness, also called myopia, is intensifying as the condition nears epidemic status in Asia and other regions, primarily in developed countries. In the United States nearsightedness has increased by more than 65 percent since 1970[i]. Though myopia is often inherited, researchers are now assessing environmental factors to help explain why myopia rates are rising so rapidly in some populations[ii].

In one of the new studies, an elementary school in Taiwan required its 333 students to spend recess outdoors for a year from 2009-10 so that researchers could learn whether this would reduce myopia rates. A similar school nearby served as the control group and did not require outdoor recess. The children in the intervention school, many of whom had formerly spent recess indoors, now spent a total of 80 minutes per day outdoors.

Students at both schools received eye exams at the study outset and one year later. The results showed that significantly fewer children became nearsighted or shifted toward nearsightedness in the school that required outdoor recess, compared with the control school. The researchers recommend that elementary schools in Asia and other regions add frequent recess breaks and other outdoor activities to their daily schedules to help protect children's eye development and vision.

"Because children spend a lot of time in school, a school-based intervention is a direct and practical way to tackle the increasing prevalence of myopia," said the leader of the study, Pei-Chang Wu, M.D., Ph.D., of Kaohsiung Chang Gung Memorial Hospital in Kaohsiung, Taiwan.

A separate study on the impact of daylight exposure on eye development analyzed data collected in a 2005 clinical trial that included 235 Danish school children with myopia. The participants were divided into seven groups, each of which represented a different seasonal interval. Because daylight hours fluctuate markedly with the seasons in Denmark, from seven hours in winter to nearly 18 in summer, access to daylight was distinct for each group. Axial eye length — the distance from the front to the back of the eye — and vision were tested in each group of children at the beginning and end of their seasonal interval. Axial length is an important measurement because elongation of the eye indicates that the person's myopia is worsening. In the children with access to the fewest hours of daylight, eye growth averaged 0.19 mm; in those with access to the most daylight, eye growth was just 0.12 mm.

"Our results indicate that exposure to daylight helps protect children from myopia," said the leader of the study, Dongmei Cui, M.D., Ph.D., of Sun Yat-sen University, China. "This means that parents and others who manage children's time should encourage them to spend time outdoors daily. When that's impractical due to weather or other factors, use of daylight-spectrum indoor lights should be considered as a way to minimize myopia."

Note to media: Contact Media Relations to request full texts of the studies and arrange interviews with experts

[i] Increased Prevalence of Myopia in the United States between 1971-1972 and 1999-2004. Arch Ophthalmol 2009;127(12):1632-1639

[ii] High heritability of myopia does not preclude rapid changes in prevalence.Clin Experiment Ophthalmol 2002;30:168 –72.

About the American Academy of Ophthalmology

The American Academy of Ophthalmology — headquartered in San Francisco — is the world's largest association of eye physicians and surgeons — Eye M.D.s — with more than 32,000 members worldwide. Eye health care is provided by the three "O's" – ophthalmologists, optometrists, and opticians. It is the ophthalmologist, or Eye M.D., who can treat it all: eye diseases, infections and injuries, and perform eye surgery. The Academy's EyeSmart® public education program works to educate the public about the importance of eye health and to empower them to preserve their healthy vision, by providing the most trusted and medically accurate information about eye diseases, conditions and injuries. Visit www.geteyesmart.org to learn more.

About Ophthalmology

Ophthalmology, the official journal of the American Academy of Ophthalmology, publishes original, peer-reviewed reports of research in ophthalmology, including basic science investigations and clinical studies. Topics include new diagnostic and surgical techniques, treatment methods, instrument updates, the latest drug findings, results of clinical trials, and research findings.Ophthalmology also publishes major reviews of specific topics by acknowledged authorities.