Choosing Sunglasses – More Than Meets the Eye

Choosing Sunglasses – More Than Meets the Eye


A Primer on UV Light

The sun can have serious consequences for your eye health. Approximately 10% of sunlight consists of ultraviolet light (UV), an invisible type of radiation. Ultraviolet light is a type of electromagnetic radiation, as are radio waves, infrared light, X-rays and gamma-rays. UV light falls between x-rays and visible light on the electromagnetic radiation spectrum. It has the power to break chemical bonds and can produce free radicals. These processes are harmful to living tissue, including those found in the eye.

Only 1% of all UV light from the atmosphere reaches the retina, the eye’s photographic film. Most UV light is absorbed and filtered at the level of the cornea and the internal crystalline lens. This absorption can damage the eye, leading to eye diseases that can jeopardize your vision. They include: photokeratitis, cancers of the eyelids, growths on the conjuctiva and cornea called pinguecula and pterygium, cataracts and macular degeneration.

The Risks of UV Light

UV light exposure is greatest between the hours of 10 a.m. and 2 p.m. However, due to the angle of the sun and the phenomenon of light reflection, UV light poses the greatest danger to the eye between 8 a.m. and 10 a.m., and 2 p.m. and 4 p.m. Even when it’s cloudy, UV light is still present. The effects of UV light on the eye are cumulative over time, which means reducing exposure throughout life is the best way to safeguard your vision. In fact, 80% of our lifetime UV exposure is reached by the age of 18. You are never too young to start protecting your eyes.

Photokeratitis and cataracts are two of the most common ocular conditions caused by prolonged UV exposure. Photokeratitis, or ‘snow blindness’, is akin to a sun burn. The cornea becomes irritated after intense sunlight exposure. This is most common while skiing or at the  beach, where individuals are exposed to high amounts of UV reflected off the snow, water or sand surfaces while not wearing sunglasses. Symptoms of photokeratitis can be seen usually 24 hours after the initial UV exposure and include blurred vision, light sensitivity and watery, painful eyes.

UV radiation can cause the proteins in the crystalline lens to be altered and lead to cataracts. This causes the normally clear lens and vision to become cloudy. Surgery is required to remove the cloudy lens when the vision becomes reduced to the point that a person has problems seeing clearly (even with the best possible prescription glasses), or is very sensitive to glare, such as that produced when exposed to bright lights (e.g. headlights).

Macular degeneration is the most common cause of vision loss among adults over the age of 50. The main cause of this is UV light exposure. The retina becomes damaged over time, and leads to mostly gradual vision loss, although at times it can be sudden. There is currently no known cure for the disease.

Solar maculopathy is another serious eye disease caused by exposure to UV light. Solar maculopathy is not reversible and results in a burn to the retina, that part of the eye’s photographic film. As there are no pain receptors in the retina, individuals are unaware of significant exposure until the damage has been done.

Cancer of the Eyelids

Basal cell carcinoma is one of the most common types of skin cancer and is often found on the eyelid margins. Sebaceous cell carcinoma, although less common, can be a highly malignant form of cancer also affecting the eyelid region.  Loss of eyelashes, frequent bleeds in lesions on the lids, and malformation of the lid margins are common signs of these types of cancers when they affect the eye lids. Those prone to these types of cancer often have a history of chronic sun exposure, such as having an outdoor profession (e.g. brick layer).

The risk of all UV related eye diseases can be greatly diminished by wearing appropriate sunglasses and, of course, never staring directly at the sun.

Choosing the Best Sunglasses

Sunglasses are necessary for preventing eye health problems caused by ultraviolet light. By ensuring your sunglasses block UV rays and wearing these sunglasses during all daylight hours, you reduce your risk for eye irritation, disease and potentially sight-threatening eye damage. There are many options available when choosing sunglasses so it’s important to pick the right sunglasses that offer both eye protection and visual performance.

First, when looking for sunglasses, make sure they block out 100% of UVA and UVB rays.
When choosing a sunglass lens tint, you want the tint to be dark enough so that even on the brightest of days you never have to squint while wearing your sunglasses.

Photochromic or Transitions lenses adapt their tint intensity depending on the brightness conditions. They get darker in sunny conditions and lighter in shade on overcast days.
Polarized lenses have a filter that blocks out all the light reflected by horizontal surfaces, such as the pavement and snow-covered areas. This reflected light not only interferes with vision by producing glare, but is a major source of eyestrain.  Polarized lenses have the ability to sharpen your vision on sunny days, and even allow you to see through car windshields ahead of you so you can better respond to changing traffic conditions. Polarized lenses at the beach allow you to see right through water, because they block the sunlight that is reflected from the top layer. Lenses can be both polarized and photochromic to give you the best of both types of lenses.

While wearing sunglasses, it still may be possible for UV light to reach the eyes and surrounding area from around the sunglasses or by reflecting off the back surface of the lens. This is why it’s so important to consider the fit of your sunglass frames. An anti-reflective coating on the back lens surface can be beneficial when the sunglasses do not wrap around your face or do not adequately block light from the sides.

If you are going to be wearing sunglasses they should rest comfortably on the bridge of your nose. They should line up with or above the brow and sit near the cheek, without resting on it otherwise lens fogging is likely to occur. Make sure your eyelashes don’t rub against the back of the lens while blinking, as this can be a major irritation and contribute to the lenses getting dirty quickly. Sunglasses with a good fit will have the added benefit of shielding the ocular tissues from wind, dust, and allergens.

Wearing sunglasses can help ensure healthy eyes in the long term, thereby safeguarding your vision. Don’t delay any longer! Contact the eye care office of Dr. Sciberras for your eye health and frame consultation today; or read more about tips to buying the best-suited sunglasses for you.

Watch each of these videos to learn more about a) UV lenses   b) polarized lenses   c) tinted lenses