How to Choose Sunglasses That Truly Protect Your Eyes

Sunglasses are often treated as a fashion accessory, but their most important job is medical: protecting your eyes from ultraviolet (UV) radiation and from glare that can strain your eyes and reduce safety. Long-term UV exposure is associated with cataract, pterygium and pinguecula, skin cancers of the eyelids and, in high doses, painful burns of the cornea. Choosing the right pair is easier than many people think once you know what to look for on the label.

This guide explains what UV400 really means, the difference between darkness and protection, when polarised lenses help, how lens colours and filter categories work, and why the shape of the frame matters. It also covers sunglasses for children and the question everyone asks: are expensive sunglasses better than cheap ones?

Why UV protection matters

Sunlight contains visible light, infrared and ultraviolet radiation. Most UVC is absorbed by the atmosphere, but UVA and UVB reach the ground. The cornea and lens absorb most UV before it reaches the retina, which is exactly why these structures can be damaged by cumulative exposure.

• Short term: intense exposure, especially from snow, water or sunbeds, can cause photokeratitis, a sunburn of the cornea that causes severe pain, watering and light sensitivity a few hours later. Read more in our article on snow blindness and UV damage.
• Long term: according to the WHO, UV exposure is a risk factor for cataract, and it is linked to pterygium, pinguecula and cancers of the eyelid skin and the surface of the eye.

UV levels are highest around midday, in summer, at high altitude, near the equator and when light is reflected from snow, sand or water. Clouds reduce UV less than people expect, so protection is useful even on overcast days.

Understanding UV400

UV400 means the lenses block radiation with wavelengths up to 400 nanometres, which covers all UVA and UVB. Labels such as 100% UV protection or UVA/UVB 100% mean essentially the same thing. In Europe, look for the CE mark and compliance with the standard EN ISO 12312-1; in the US, sunglasses must meet ANSI Z80.3 requirements. In Australia and New Zealand, AS/NZS 1067 applies.

Filter categories 0 to 4

Filter categories, defined in the international standard, describe how much visible light the lens lets through. They say nothing about UV protection, which must be stated separately.

For most people in everyday summer conditions, category 2 or 3 lenses are a good choice. Category 4 lenses are reserved for extreme glare and are unsafe for driving because they block too much light. No tinted lens, including yellow so-called night lenses, should be worn for driving after dark, a point we cover in our article on night driving.

Polarised lenses: what they do and do not do

Light reflected from flat surfaces such as water, wet roads, snow or a car bonnet becomes partly polarised, mostly in the horizontal direction. This produces intense glare. Polarised lenses contain a filter that blocks horizontally polarised light, cutting this glare dramatically.

Benefits:

• Much less glare from water, making them popular for fishing, sailing and beach use.
• More comfortable driving in bright, wet conditions.
• Improved contrast and reduced squinting.

Limitations:

• Polarisation does not provide UV protection by itself; check for UV400 separately (most quality polarised lenses have it).
• They can make it hard to read some LCD screens, such as car displays, phones or aircraft instruments, which may appear dark or patchy at certain angles.
• Some skiers prefer non-polarised lenses because polarisation can make icy patches harder to see.

Lens colours

Lens colour affects comfort and contrast, not UV protection. Common options include:

• Grey: reduces brightness evenly with minimal colour distortion; a good all-round and driving choice.
• Brown and amber: increase contrast and depth perception, useful in variable light, for golf and on the road.
• Green: a balance of contrast and natural colour perception.
• Yellow and orange: increase contrast in low light and haze, but transmit a lot of light; not suitable for bright sun or for night driving.
• Mirrored coatings: reflect extra light, useful in very bright conditions such as snow and water.
• Gradient lenses: darker at the top and lighter at the bottom, convenient for driving and reading the dashboard.

If you have a colour vision deficiency, strongly tinted lenses may make it harder to distinguish traffic lights; grey lenses are usually the safest choice.

Frame shape and coverage

A lot of UV reaches the eye from the sides, above and below the lenses, and from reflections off the back of the lens. Coverage matters as much as lens quality.

• Wraparound designs or frames with wide temples reduce light entering from the sides.
• Larger lenses protect the delicate skin around the eyes, where skin cancers are common.
• A close fit to the face, without pressing on eyelashes, limits stray light.
• An anti-reflective coating on the back surface reduces UV reflected into the eye.
• A wide-brimmed hat can reduce UV reaching the eyes considerably and works well combined with sunglasses.

For sport, choose impact-resistant lenses such as polycarbonate or Trivex. Our guides to sunglasses and safety and sports eyewear go into more detail.

Prescription and photochromic options

If you wear glasses, you can choose prescription sunglasses, clip-ons, fit-over sunglasses, or photochromic lenses that darken in UV light. Photochromic lenses are convenient but have limitations: they darken less behind car windscreens, which block much of the UV that activates them, and they take time to lighten when you go indoors. Ask your optician about the best option for your lifestyle. Most modern clear spectacle lenses, especially polycarbonate and high-index, already block much or all UV.

Sunglasses for children

Children spend more time outdoors than most adults, and their eyes transmit more UV to the inner structures, because the natural lens is clearer in childhood. Sun protection in childhood is therefore important. At the same time, time outdoors is very good for children's eyes and may reduce the risk of myopia, so the aim is protection, not avoidance; see our article on outdoor time and myopia.

• Choose genuine sunglasses with UV400 or 100% UV labelling, not toy sunglasses without proper filters.
• Use impact-resistant lenses and flexible, durable frames.
• Pick a comfortable fit, perhaps with a strap for small children.
• Combine with a wide-brimmed hat and shade, especially in the middle of the day.
• Babies under six months should be kept out of direct sunlight.

Cheap vs expensive sunglasses

Price is not a reliable guide to UV protection. Inexpensive sunglasses from reputable retailers that meet recognised standards can provide excellent UV protection. What higher prices may buy:

• Better optical quality, with less distortion.
• More durable lenses and frames, scratch-resistant coatings and better hinges.
• High-quality polarisation and anti-reflective coatings.
• Lighter materials and better fit.
• Brand name and design.

The real risk lies in unlabelled sunglasses from unknown sources, where neither the UV filter nor the optical quality can be trusted. If you are unsure, many opticians can test the UV transmission of your sunglasses with a simple device.

Situations that need extra protection

Some environments raise UV exposure far above everyday levels, and ordinary fashion sunglasses may not be enough:

• Snow and mountains: fresh snow reflects a large share of UV, and UV intensity increases with altitude. Use category 3 or 4 wraparound lenses or goggles, and never ski or hike above the snow line without them.
• Water sports and beaches: water and sand reflect UV and glare. Polarised category 3 lenses with a retaining strap are practical.
• Outdoor work: farmers, builders, lifeguards and other outdoor workers accumulate high lifetime doses. Employers should provide suitable protective eyewear; see our guide to eye care by profession.
• After eye surgery or with certain medicines: after cataract surgery or with photosensitising medicines, your eyes may be more sensitive to light. Ask your doctor whether extra protection is advisable.
• Sunbeds and welding: these require specific certified protective goggles; ordinary sunglasses are not adequate.

When to see a doctor

Sunglasses protect the eyes, but they do not fix existing problems. See an eye care professional if you notice:

• Severe eye pain, redness, watering and light sensitivity a few hours after time in snow, on water or under a sunbed, which can signal photokeratitis.
• Persistent sensitivity to light even in moderate brightness, which can be a sign of eye inflammation or other conditions.
• A growth on the white of the eye that is enlarging or creeping onto the cornea.
• A changing spot, lump or non-healing sore on the eyelid.
• Gradual blurring, glare or fading of colours, which may indicate cataract.