As we age, the sun's rays become increasingly dazzling and painful to our eyes. When selecting sunglasses, it is good to know that different lens colors each have their own properties.
Sunlight is composed of rays of varying wavelengths, including, in ascending order, ultraviolet, blue, green, yellow, red and infrared. Ultraviolet and infrared light are invisible to the naked eye. Electromagnetic energy increases as wavelengths become shorter, and exposing the eyes to short wavelengths for long periods of time should be avoided.
In the Environment Ministry's "Health Care Manual for UV 2008," which introduces the latest scientific findings and related information on UV, the effects of aging and ultraviolet light are cited as risk factors for developing cataracts. When a cataract forms, the lens of the eye becomes clouded and scatters light, which gives the feeling of dazzling brightness and reduces visual acuity. If patients with mild, early-stage symptoms are included, 100 per cent of people aged 80 or older develop cataracts, some research data suggests.
In recent years, there has also been an increase in cases of age-related macular degeneration, whereby visual acuity declines as the central area of the retina ages. Experts indicate that ultraviolet rays and other short-wavelength lights are contributing factors.
Jun Kozaki, director of the Kozaki Eye Clinic in Osaka, said: "It is easier to halt the development of eye diseases if they are detected and treated at an early stage. People who feel that sunlight is glaringly bright due to light scattering should wear sunglasses to make themselves more comfortable."
When choosing the right sunglasses, Masami Kondo at Miki Optical Institute, which researches eyes and glasses in Okayama, said it is best to wear sunglasses that have ultraviolet protection.
"Additionally, since the way light passes through the lenses depends on their colour, people should select sunglasses with the colour that best suits them."
Yellow is the colour that best blocks out potentially harmful short-wavelength light and suppresses glare caused by light scattering, followed by brown. Although gray lenses are not as good at blocking short wavelengths as yellow and brown ones, they do block out all wavelengths of light in an almost uniform fashion.
Meanwhile, yellow lenses are not very effective at reducing the amount of light that enters the eyes. For this reason, many lenses are a mixture of yellow with brown or gray.
Although it may be true that the darker the colour, the more effective lenses will be at reducing glare, some experts point out that this can actually cause the pupils to dilate and admit more light.
"The rule of thumb is to get lenses that are not so dark that the pupils can barely be seen through them. People with sunglasses like this don't need to worry about their pupils dilating too much," Kondo said.
There is also a type of lens that has a gradient. An 88-year-old man from Amagasaki, Hyogo Prefecture, who had cataract surgery 11 years ago, uses this type.
"They are very convenient, as I just need to look through the transparent area at the bottom of the lenses when I want to see the true colour of something," he said.
Another recommendation is to select large sunglasses that fit snugly so that less light comes in from the gap between them and the face. In order to check how things look under natural light with sunglasses, it is suggested that customers ask the store if it is possible to try them on outside the building.
Protection against sunlight exposure is made even more effective by wearing a hat or using a parasol in addition to sunglasses.
■ Points to keep in mind when selecting sunglasses
(Based on suggestions from Masami Kondo at Miki Optical Institute )
・Select lenses with ultraviolet protection
・Lenses should be translucent enough so that the pupils can be seen through them
・Choose large lenses with minimal gaps between the sunglasses and the face
・Try them on under natural light on a sunny day
・Check your overall appearance in a full-length mirror
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