2024-06-05
The Mountains Will Damage Your Eyes If You Let Them
Mountain climbing is one of the few recreational activities where forgetting your sunglasses can cause a genuine medical emergency. At altitude, UV radiation intensifies dramatically — roughly 10 to 12 percent stronger for every 1,000 metres of elevation gain. Add snow and ice reflecting up to 80 percent of UV light back at your face, and your eyes are being bombarded from above and below simultaneously.
Snow blindness (photokeratitis) is a real and painful condition. It is essentially a sunburn on your cornea. Symptoms include intense pain, tearing, swelling, and temporary vision loss — usually hitting 6 to 12 hours after exposure. At high altitude with no shelter, that can turn a climb into a survival situation. Even below the snow blindness threshold, cumulative UV exposure at altitude accelerates cataract formation and can damage the retina over time.
The sunglasses you wear around town are not built for this. Mountain climbing demands specific eye protection designed for extreme UV, intense glare, and harsh conditions.
UV at Altitude: The Numbers
Understanding why altitude changes the equation helps you take it seriously.
- Sea level: Baseline UV index. The atmosphere filters a significant portion of UV-B radiation.
- 2,000m (Lake Louise area): UV is roughly 20 to 25 percent stronger than at sea level.
- 3,000m (Columbia Icefield): UV is 35 to 40 percent stronger. Snow reflection can effectively double exposure.
- 4,000m+ (high alpine): UV is 50+ percent stronger. With snow reflection, effective UV exposure can be 3 to 4 times what you experience at sea level.
Most people significantly underestimate UV exposure in the mountains because temperature and UV intensity are not correlated. A cold, overcast day at 3,000m can deliver more UV to your eyes than a hot beach day at sea level. Clouds scatter UV but do not block it effectively — up to 80 percent of UV penetrates cloud cover.
Lens Category: What the Numbers Mean
Sunglass lenses are rated by visible light transmission (VLT) — the percentage of light they let through. For climbing, this is critical.
| Category | VLT | Use |
|---|---|---|
| Cat 0 | 80-100% | Clear or very light tint. Indoor use, overcast valleys. Not for climbing. |
| Cat 1 | 43-80% | Light tint. Overcast conditions at lower elevations. Not enough for above treeline. |
| Cat 2 | 18-43% | Medium tint. General outdoor use. Adequate for lower elevation scrambles without snow. |
| Cat 3 | 8-18% | Dark tint. Standard for most mountain climbing. Good for bright sun and moderate snow. |
| Cat 4 | 3-8% | Very dark. Glacier travel, high alpine, heavy snow. Too dark for driving or low light. |
For general mountain climbing in the Canadian Rockies, Category 3 is the minimum. For glacier travel, scrambles with significant snow exposure, or any climb above 3,000m, Category 4 is strongly recommended. Some climbers carry both — Cat 3 for approaches through forest and Cat 4 for above treeline.
Polarization on Mountains: Yes or No?
Polarized lenses eliminate horizontal glare from flat reflective surfaces. On a glacier or snowfield, the glare reduction is transformative — snow that would otherwise be a blinding white sheet becomes readable terrain with visible texture, shadows, and contours.
However, polarized lenses can reduce your ability to see ice on rock. Thin ice sheets reflect light directionally, and polarization can make them less visible. This matters on mixed terrain, alpine rock routes, and any approach with potential for verglas (thin ice on rock).
The practical recommendation: polarized for snow-dominant terrain (glaciers, snowfields, ski approaches). Non-polarized for mixed rock and ice where reading ice conditions on rock is critical. If you only carry one pair, polarized Cat 3 or 4 covers the majority of climbing situations well.
Frame Features for Climbing
Side Shields and Wraparound Coverage
At altitude, UV and reflected light enter from every angle — including the sides and below. Standard sunglasses leave significant gaps at the temples where light floods in, causing squinting and peripheral UV exposure. Climbing sunglasses need either built-in side shields (leather or rubber panels that block peripheral light) or a deep wraparound curve that achieves the same effect.
Removable side shields are ideal because they let you configure for conditions: shields on for glacier travel and snowfields, shields off for lower-elevation approaches where peripheral vision matters more.
Ventilation and Anti-Fog
Climbing is hard work, and you will sweat even in cold temperatures. Lenses fog when warm, humid air from your face hits the cooler lens surface. Frames with ventilation gaps at the top or between the lens and frame allow airflow that prevents fogging. Anti-fog coatings on the inner lens surface provide additional protection.
Fogged lenses at a critical moment — a crevasse crossing, an exposed scramble, a route-finding decision — are genuinely dangerous. Prioritize ventilation in your frame choice.
Retention and Security
Dropping your sunglasses on a glacier is not an inconvenience — it is a hazard. A retainer strap is mandatory for mountain climbing. Choose a frame with strap-compatible temple tips (holes or textured ends that grip the strap). Some climbing-specific frames have integrated retainer attachment points.
The frame itself should grip securely over a balaclava, buff, or beanie without shifting. Test the fit with your typical headwear — a frame that fits perfectly on bare skin may not grip at all over a merino buff.
Helmet Compatibility
If you climb with a helmet, your sunglasses need to fit comfortably underneath it. Thick temples or wide frames can create pressure points under a helmet brim. Low-profile temples and a frame that sits close to your face work best. Try your sunglasses on with your helmet before committing.
Durability
Mountain environments are harsh on gear. Temperature swings from -20C to +30C, rock abrasion, pack compression, and UV exposure all degrade materials. Polycarbonate or NXT (Trivex) lenses resist impact and temperature shock better than glass. Nylon or grilamid frames flex without breaking in cold temperatures, where acetate and cheap plastics become brittle.
Lens Tint for Mountain Conditions
- Brown or copper: The best all-round mountain tint. Enhances contrast on snow and rock, making terrain features more readable. Improves depth perception on flat snow surfaces.
- Grey: True colour representation. Good for bright conditions where you want accurate colour without enhancement. Some climbers prefer grey for route-finding on mixed terrain.
- Rose or vermillion: Excellent contrast in flat light and overcast conditions. Makes shadows and terrain features visible on days when everything looks uniformly white.
- Photochromic: Adapts to changing light automatically. Useful for long days with varying conditions — forest approaches to alpine ridges. Most photochromic lenses darken to Cat 3 but not Cat 4, so they may not be dark enough for glacier travel.
Prescription Options for Climbers
If you need vision correction, you have the same three options as other sports, but the stakes are higher in the mountains.
- Prescription climbing sunglasses: The most reliable option. Your exact prescription in a climbing-specific frame with Category 3 or 4 lenses and side shields. No risk of losing a contact lens in cold, dry, dusty alpine conditions.
- Contact lenses + non-prescription climbing sunglasses: Works well for many climbers. Daily disposable contacts eliminate the hygiene concerns of reusable lenses in multi-day mountain environments. Carry a backup pair of glasses in your pack in case a lens tears or dries out.
- Prescription inserts: An inner frame with your prescription behind the main climbing lens. Adds slight bulk and can fog more easily, but lets you use any climbing-specific frame.
Common Mistakes Climbers Make
- Wearing fashion sunglasses at altitude. Standard sunglasses are typically Category 2 — far too light for above treeline. They also lack side protection.
- Forgetting sunglasses on overcast days. UV penetrates clouds. Snow blindness can occur on cloudy days, especially at altitude. Always carry your sunglasses on any mountain day.
- Storing sunglasses on top of your head. On a glacier or snowfield, the minutes between taking them off "just for a second" and putting them back can deliver a surprising UV dose. Use the retainer strap and wear them consistently.
- Not having a backup. If your only pair of sunglasses breaks or is lost on day one of a multi-day trip, you have a serious problem. Carry a cheap pair of Category 3 sunglasses as a backup, or at minimum, bring duct tape and cardboard to improvise emergency snow goggles with narrow slits.
Protecting Your Long-Term Vision
Occasional UV overexposure may only cause temporary discomfort, but cumulative exposure over years of mountain climbing contributes to early cataract formation and macular degeneration. Treating your climbing sunglasses as essential safety equipment — not an optional comfort item — protects both your immediate safety and your long-term eye health.
If you are a regular mountain climber and it has been a while since your last eye test, come in and let us check your eyes. We can also help you choose the right lens category, tint, and frame for your specific climbing objectives — whether that is weekend scrambles in Kananaskis or glacier routes in the Columbia Icefield.