Rumor has it sunglasses are good for your eyes, and sunglasses are bad for your eyes. We spoke with ophthalmologist Tongalp Tezel, MD, to separate fact from fiction when it comes to protecting your eyes from the sun.
Ultraviolet radiation
The sun is a source of ultraviolet (UV) radiation. When you're outside in the sun you're exposed to two types of UV rays: UVA and UVB.
UVA and UVB can penetrate and change your skin and eye cell structure-causing burns and injuries-putting you at risk of skin cancer and eye diseases that can lead to permanent vision loss.
The harmful effects of UVA and UVB to the eyes include:
Cataracts
A cataract is a cloudiness of the lens in the eye. The lens bends incoming light rays and focuses them onto the retina. Human lenses must be clear to transmit the light without any scattering and loss. Lenses gradually get cloudy after age 30, and by your 60s and 70s, cloudiness decreases the amount of light penetrance into the eye and scatters the incoming light. For this reason, people with cataracts have dim and fuzzy vision. Aging is the most common cause of cataracts, but UVB accelerates cataract formation. In people who are exposed to UVB over a long period of time, lens opacities usually develop in the parts exposed directly to sunlight. It is estimated that cataract formation can be reduced by roughly 5% with appropriate UV protection.
Age-related macular degeneration
Exposure to high levels of sunlight may increase the risk of age-related macular degeneration, an eye disease that may lead to loss of central vision, by almost three-fold.
Cancers
Eyelid tumors such as basal cell carcinoma and squamous cell carcinoma, as well as intraocular tumors such as uveal melanoma, are associated with greater UV exposure.
Cornea and conjunctiva damage
Basically, sunburn of the cells on the front of the eye, and it's painful. In many cases of photokeratitis (damage to the cornea) and photoconjunctivitis (damage to the thin layer of tissue covering the eye), these eye injuries usually heal on their own if you completely avoid sun for a week. And you can decrease the risk of sun-related damage to your eye with appropriate sunglasses.
Are sunglasses good for your eyes?
Sunglasses are good for your health if the lenses block UV and the sunglasses are worn correctly (with the frame's nose bridge touching your face).
Eyes filter out most, but not all, UV rays. Anything that limits UV exposure to the eye alleviates risk. Sunglasses protect your eyes and also can protect the skin around the eyes.
Can wearing sunglasses damage your eyes?
Sunglasses are bad for your eyes if they are used the wrong way or do not block UV.
Eyes adapt to ambient light, and pupils dilate when light is dim or you're wearing dark sunglasses. That creates a bigger area for UV to access the eye. If the lenses are simply colored and do not block UV, you're opened up to eye damage.
What are the best sunglasses for your eyes?
The ones you wear properly, fitted to your face. If you create space between the frames and eyes by pulling your glasses forward, for example, and don't cover all of your eyes, you're completely at the mercy of the sun's UV rays.
- Expensive glasses do not guarantee better UV protection.
- Bigger frames can offer more coverage, but people wearing bigger frames often slide the glasses down the nose since they feel their eyes are covered too much. That's not good.
- Small sunglasses are a public health hazard. John Lennon size is small.
- Wrapped shapes are best. About 20% of UV enters the eye from reflective light that comes in from the side: Wraparound designs or side shields are recommended, especially with darker shades.
- Antireflective coatings can increase UV exposure by causing back reflection of the UV rays into the eye.
- There's no such thing as sunglasses that are too dark. However, dark lenses can be harmful if they do not offer good UV protection or if UV rays reach the eye from the sides.
Not all lenses claiming to absorb 100% of UV can indeed block all UV wavelengths. In the United States, manufacturers are allowed to claim 100% UV protection for lenses that absorb ultraviolet rays with wavelengths up to 380nm even though the range of ultraviolet rays extends up to 400nm.
Be sure that your sunglasses can block all UV rays up to 400 nm. This becomes an important issue for retina protection in kids since their lenses are more transparent to UV compared to adults.
Do contact lenses provide UV protection?
Ultraviolet-absorbing soft contact lenses cannot provide full protection against the detrimental effects of UV to the eye. But they can complement the protection supplied by UV-blocking glasses, especially in blocking the entry of reflected UV rays into the eye, if the contacts are well-fitted and of sufficient diameter.
Polarized sunglasses
UV protection and polarization are not the same. Polarization can alleviate glare. Glare is a reflection from surfaces, like water or roads. Polarized lens filter light by only allowing in certain wave lines, decreasing the scattering that causes glare. It's something you might need in addition to UV protection, not a replacement.
References
Tongalp Tezel, MD, is head of the retina service in the Department of Ophthalmology at Columbia University Vagelos College of Physicians and Surgeons. He is an internationally known clinician-scientist and a leader in the management of vitreoretinal diseases.
