Dark lenses without a UV filter are more dangerous than no glasses at all: behind them the pupil dilates and lets in more UV than without glasses. So the first thing to look at is not color or brand, but the label.
What UV400 Means
UV400 means the lens blocks all rays up to 400 nanometers — i.e. 100% of UVA and UVB. This is the maximum eye protection that exists. "100% UV protection" and "UV 100%" are synonyms for UV400.
What Sun Does to Eyes
- Photokeratitis — corneal burn ("snow blindness"): snow, water and mountains multiply UV;
- Cataracts — WHO data: up to 20% of cases are caused by UV;
- Pterygium — tissue growth on the cornea ("surfer's eye");
- Macular degeneration — retinal aging, leading cause of blindness in seniors.
Sunglasses Labels: How to Read
| Label | Meaning |
|---|---|
| UV400 / 100% UV | full protection — what you need |
| Category 0–1 | light lenses: cloudy, indoors |
| Category 2–3 | city and bright sun — daily optimum |
| Category 4 | mountains, glaciers, sea; illegal to drive with |
| Polarized | removes glare but does NOT guarantee UV protection — look for UV400 separately |
Category is the tint, UV400 is protection. You need both: category 2–3 + UV400.
When Sunglasses Are Mandatory
- at UV index 3 and above;
- near water, snow and sand — reflection adds up to 80–90% UV;
- in mountains: +10–12% UV per 1000 m of altitude;
- driving: windshield blocks UVB but lets UVA through.
Selection Checklist
- UV400 marking on the label or frame;
- lens covers the eye on the side — bigger frames are better;
- for kids — unbreakable polycarbonate, also with UV400;
- buy where they can test UV transmission with a tester (available at opticians).
Bottom Line
Sunglasses are the second most important protection after SPF: eyelid skin is the thinnest and ages first (see article on photoaging). Choose category 2–3 with UV400 and check the UV index: below 2–3 glasses are just for brightness comfort.