Sun and vision
Remember your eyes
Sunglasses offer important sun protection.
By Dr. Paul Rafuse
We all know about sunscreen and other protective measures to keep our skin safe, but what about our eyes? Sunglasses keep our eyes safe from the sun and can protect us from many eye issues.
There are many reasons to wear sunglasses outside, on both bright days and those with cloud cover. Ultraviolet (UV) light easily penetrates clouds, particularly in the summer during midday or at altitude. Given our cumulative exposure to UV radiation over our lifetime, even low levels of UV radiation have the potential to affect almost all structures of the eye and its surrounding tissues.
Your eyelids have some of the thinnest and most delicate skin on your body. They are subject to the same risk of cancer as any other sun-exposed skin surface: basal cell, squamous cell and melanoma. The lower eyelid is particularly prone to basal cell carcinoma. Pre-cancerous actinic keratoses, which can progress to squamous cell malignancies, have a preference for the corners of the eyelids.
The cornea, the clear dome-shaped window of the eye, can get enough of a “sunburn” that dry eye symptoms can be generated or greatly aggravated. An extreme example of this is the snow blindness suffered by skiers who forget their sunglasses or goggles. The shorter UVB wavelengths are responsible for the formation of pingueculae, small fleshy nodules at the junction of the cornea and sclera (white of the eye) at the three and nine o’clock positions. Pingueculae can grow across the cornea as a pterygium, which can be cosmetically unacceptable and lead to visual distortion.
Clouding of the natural lens (nuclear sclerotic cataract) is a normal effect of aging, but cortical cataracts are associated with exposure to UV light without proper eye protection. These typically occur at a much younger age (to people in their 40s and 50s) rather than the usual age group of those in their 70s or 80s who develop nuclear sclerotic cataracts. The damage probably starts in childhood.
The number one cause of blindness in Canada is age-related macular degeneration, which is caused by a number of genetic and environmental factors. One of the alleged modifiable risk factors is UVA and, perhaps, blue light. The evidence isn’t conclusive, but these wavelengths can be filtered to a large extent with sunglasses.
Good general-purpose sunglasses don’t have to be expensive. However, they should filter 60 to 92 per cent of visible light and UVA rays, and 95 to 99 per cent of UVB rays. They should be dark enough to be comfortable in bright light, but not so dark to reduce your vision.
Winter enthusiasts, such as alpine skiers, often carry a selection of tints for various lighting conditions. Photochromic lenses, which darken with increasing light intensity, may be adequate for moderate conditions, but may not get dark enough for very bright light. Polarized lenses are particularly useful for reflected light from the road, water or snow. The colour of the lens should be grey or a brownish green.
Sunglasses should be large enough to cover all the light-sensitive structures of the eye. Large wrap-around styles, or sport goggles, are the best choices for those who work or play outdoors, and a broad-brimmed hat is a good idea too. Don’t forget your children – since much eye damage begins at a young age, children should protect their eyes from the sun by wearing sunglasses as soon as they venture outside.
Dr. Paul Rafuse is the President of the Canadian Ophthalmological Society and an Associate Professor in the Department of Ophthalmology and Visual Sciences, Dalhousie University, Halifax, Nova Scotia. He is a past President of the Canadian Glaucoma Society and chaired the Expert Committee authoring the Canadian Ophthalmological Society’s Clinical Practice Guidelines for the Management of Glaucoma in the Adult Eye.
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