New research finds greater UV exposure to eyes

Fri 15th February 2008

New research conducted in Japan found that during spring, summer and autumn, Ultraviolet (UV) exposure to the eye during early morning and late afternoon was approximately double that of the mid-morning/early afternoon period that is most often thought of as peak sun exposure time.

Using a specially designed model to measure and record the amount of UV-B rays entering the eye from sunrise to sunset, researchers at Kanazawa Medical University concluded that eyes are at greater risk to UV exposure at times that many individuals may not be taking proper steps to protect their eyes. The findings from the study were presented at the 111th Annual Meeting of the Japanese Ophthalmological Society in Osaka  (April 19-22).

"While it has long been thought that the risk of UV exposure to the eyes is greatest during the mid-day hours, from 10:00 AM to 2:00 PM, this study suggests that from spring through fall, when the days get longer, the incidence of exposure is actually greatest earlier and later in the day," said lead researcher Professor and Chairman Hiroshi Sasaki, Department of Ophthalmology, Division of Sensory Organ Medicine, Kanazawa Medical University.

"This study further demonstrates the need for all day UV protection of your eyes," added Cristina Schnider, O.D., Director, Medical Affairs, Vistakon, Division of Johnson & Johnson Vision Care. "Over the long-term, the sun can cause irreversible harm to all structures of the eye and surrounding tissue that are left unprotected or under-protected. The most complete measure of UV protection can be achieved with a combination of UV-absorbing sunglasses, a wide brimmed hat, and UV-blocking contact lenses."

Research was conducted on the campus of Kanazawa Medical University in September and November 2006. After incorporating a tiny UV sensor into the ocular segment of a specially designed model, UV-B rays entering the eye were measured from sunrise to sunset. The visual line of the model was set at 15 degrees below the horizontal line (Normal line of sight when human walks) and its face followed the path of the sun from East to West, and was placed at the lower front side of the sun all the time.

The results were recorded, coupled with various conditions, such as solar altitude (position of the sun relative to the horizon) and the direction of the model's visual line (angle) or facial or head shape, in a relative manner.

On September 21, around the time of the Autumnal Equinox (one of two times a year when the sun crosses the equator, and the day and night are of approximately equal length), the two highest points in the UV exposure test to the eye were recorded around 9:00 AM and from 2:00 - 3:00 PM. UV exposure to the eye for four hours from 10:00 AM to 2:00 PM recorded nearly half of the highest UV exposure points in the morning and evening.

As the solar angle decreased (moving toward winter), peak UV exposure to the eyes moved back toward mid-day. On November 21, one of the highest points of exposure occurred around noon under the same conditions as the previous test.

UV protection is just as important during the winter, cautioned Dr. Schnider. According to the World Health Organization (WHO), while UV radiation is generally lower during winter months, snow reflection may double an individual's overall exposure. The WHO advises that fresh snow may reflect as much as 80 percent of UV rays, compared to other surfaces such as, grass, soil and water, which reflect less than 10% of UV radiation; dry beach sand (about 15%), and sea foam (about 25%).

Ultraviolet radiation reaches the eye not only from the sky above but also by reflection from surfaces such as water, sand, and pavement. While most sunglasses can help block UV rays that enter through the lenses, most frame styles do not prevent unfiltered rays from reaching the eyes from the sides, top, and/or bottom of the glasses. "Because of this, some sunglasses block as little as 50% of all UV radiation from reaching the eyes," explained Dr. Schnider. Similarly, hats with brims offer no protection from UV rays reflected up from surfaces such as pavement, sand, and water.

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