Sunglasses at Altitude — The Eye Protection That Prevents Snow Blindness
At 4,000m, UV exposure is roughly double sea level — and snow reflects up to 80% of it back at your eyes. Regular fashion sunglasses aren't enough: they let UV in around the edges and through insufficient lenses. The result is snow blindness (photokeratitis) — a painful UV burn on your corneas that hits 6–12 hours after exposure and temporarily blinds you. Proper sunglasses aren't a fashion choice on trek; they're medical equipment.
Why Altitude UV Is Different
- Thinner atmosphere = less UV filtering — every 1,000m adds roughly 10–15% more UV; at 4,000m you're getting ~50% more UV than sea level
- Snow reflection — fresh snow reflects ~80% of UV; you're getting hit from above AND below
- Cloudy days still burn — UV penetrates cloud cover; overcast doesn't mean safe
- Snow blindness is the consequence — photokeratitis is a corneal sunburn; painful, temporarily blinding, entirely preventable
What to Look For — Lens Categories
- Category 3 lenses — minimum for trekking; blocks ~80–90% visible light; the standard for most conditions
- Category 4 lenses — for snow/glacier; blocks ~95%; TOO dark for driving but correct for high-altitude snow travel
- Category 0–2 — insufficient for altitude; fashion sunglasses don't protect
- UV400 rating — blocks 100% UVA/UVB; non-negotiable regardless of category
- Polarized — reduces glare off snow/water; helpful but doesn't substitute for UV protection
Frame Design — What Matters
- Wraparound or side-shielded — the most important feature; UV enters around frame edges; wraparound or side shields block it
- Close fit — gap between frame and face lets UV in; closer to the face = better protection
- Category 4 glacier glasses — classic mountaineering style with leather/plastic side shields; the traditional and effective solution
- Lightweight — you wear them 8+ hours daily; heavy frames cause headaches and get left in the bag
- Retainer strap — glasses fall off; a retainer keeps them on your face, not lost in a stream
Nepal-Specific Advice
- Buy quality in Kathmandu — Thamel shops sell fake Julbo/Ray-Ban alongside decent house brands; inspect UV400 rating claims skeptically; bring from home if you have good ones
- Spare pair — losing your only sunglasses at 5,000m is a medical problem, not an inconvenience; pack a backup
- Contact lens wearers — sunglasses over contacts; the UV protection is even more critical for contact lens users
- Children — kids' eyes are more UV-sensitive; proper children's sunglasses matter more, not less
Snow Blindness — The Delayed Consequence
- The 6-12 hour delay — photokeratitis symptoms arrive hours after exposure; you feel fine during the damaging exposure; the burn appears that evening
- The symptoms — painful gritty eyes, light sensitivity, tearing, the feeling of sand in the eyes; temporarily blinding
- The mechanism — UV burns the cornea surface; the same way UV burns skin; the cornea is more sensitive
- The prevention is simple — the correct sunglasses worn consistently; the consequence is severe enough to justify the equipment
- Cloudy days still burn — UV penetrates cloud cover; overcast does not mean safe; the protection is needed regardless of visible sun
The Frame Fit — More Than Lens Darkness
- Wraparound is the critical feature — UV enters around frame edges; the wraparound or side-shield design blocks it; flat-fronted sunglasses fail at altitude regardless of lens darkness
- Close to the face — the gap between frame and face is where UV gets in; closer fit equals better protection
- Weight for the 8-hour day — you wear them constantly; heavy frames cause headaches and get left in the bag; lightness is compliance
- Retainer strap — glasses fall off on scrambles and stream crossings; the retainer keeps them on your face, not lost in a river
- Category 4 only where needed — the darker glacier-glass lenses are for snow/glacier specifically; Category 3 wraparound for standard trekking; the too-dark lens is its own problem
Common Questions
The UV Problem at Altitude
UV radiation increases ~10–12% per 1,000m of altitude — at 5,000m, the UV exposure is roughly double sea level. Combined with snow reflection (80% of UV reflects back), the eyes receive intense UV exposure that causes snow blindness (photokeratitis) — essentially a sunburned cornea. Sunglasses at altitude are medical equipment, not fashion.
Category 4 for Glacier
For snow/glacier travel, category 4 lenses (darkest, blocks 92%+ of visible light) with side protection are required — standard category 3 sunglasses are insufficient for the reflective environment. For non-glacier trekking, category 3 is adequate. The sunglasses left at home or inadequate for the conditions produce the snow blindness that is the trek-ender.
The UV Category
For altitude trekking: Category 3 or 4 lenses (the UV protection level), full coverage (the wraparound or the side-shielded design that prevents peripheral UV entry), and the polarization that reduces glare from snow/ice. The fashion sunglasses that are not rated for altitude UV provide inadequate protection for the mountain environment.
The Glacier Requirement
For glacier travel or high-altitude snowfields — Category 4 (the darkest lenses) and the coverage that prevents the snow blindness. The snow reflects ~80% of UV; the uncovered peripheral exposure produces the corneal burn (snow blindness) that is the temporary blindness the trekking without proper eyewear risks. The sunglasses that are inadequate produce the injury that the right lenses prevent.
The Frame Coverage
The peripheral UV entry — the sunglasses that do not cover the sides allow the UV to enter around the edges. For the altitude exposure, the wraparound design or the side shields are the complete coverage that the front-only lens does not provide. The glacier glasses' side shields are the specific design for the snow protection.
Category 4 Warning
Category 4 lenses are very dark — too dark for driving or the general walking; they are specifically for the high-altitude snow/glacier environments. For the Kathmandu valley or the lower trekking, the Category 3 is appropriate; Category 4 is for the mountaineering or the high-altitude snow exposure.
The Category 4 Requirement
For the glacier and the snow travel: the Category 4 sunglasses (the darkest category — blocks 92-98% of the visible light) are required for the high-altitude snow travel. The standard Category 3 sunglasses are insufficient for the glacier; the Category 4 that blocks more.
The Side Protection
The wrap-around or the side shields — the peripheral light that enters from the sides is the UV exposure that damages the eye. For the high-altitude snow, the glasses that provide the side coverage.
The Fit and Coverage
Sunglasses fit — the coverage that protects the periphery (the side shields or the wrap-around), the fit that is comfortable for the extended wear, and the lens quality (the optical distortion that is minimal).
The Backup Pair
The backup sunglasses — the spare pair that is carried (the loss or the breakage that would leave the eyes unprotected at altitude). For the trek, the backup that is packed.
The Frame Fit
Sunglasses frame fit — the secure fit that doesn't slide on the nose (the sweating that loosens), the wrap that covers the peripheral, and the temple length that is comfortable.
The Backup
Sunglasses backup — the pair that is carried in case of the loss or the damage. For the critical eye protection, the backup that is essential.
The Fit
Sunglasses fit — the wraparound (the side that is also protected), the temple that is snug (the not so tight that produces the headache), and the lens that covers the field.
The Backup
Sunglasses backup — the spare pair that is carried (the loss or the breakage that is common). For the trek, the backup that is essential.
The Cost
Sunglasses cost — the quality Cat 4 ~$80-200 (the glacier that is rated) vs the budget that may not protect. For the high altitude, the proper that is essential.
The Fake Risk
Kathmandu fake sunglasses — the dark but the no UV (the harmful that worsens). For the purchase, the verified UV that is checked.
The Fake Risk
Sunglasses counterfeit — the Kathmandu ~$5-15 fake (the UV-uncoated that harms more than protects). For the purchase, the genuine that is verified.
The Glacier Need
Glacier glasses — the Category 4 ~$50-150 (the high- altitude that prevents the snow blindness). For the pass, the dark that is required.
The Genuine
Sunglasses genuine — the ~$30-120 (the UV-rated that is required). For the glacier, the real that is the safe.
The Cat-4
Glacier glasses — the ~$20-80 (the category-4 that is needed). For the high-snow, the rated that is the protection.
Why are special sunglasses needed for trekking?
UV exposure roughly doubles every 1,000m of altitude gain; snow reflects 80% of it back at your eyes. Regular fashion sunglasses let UV in around the edges and have insufficient lenses. The consequence is snow blindness (photokeratitis) — a painful corneal burn that temporarily blinds you. Proper sunglasses are medical equipment at altitude, not fashion.
What lens category do I need for trekking?
Category 3 minimum for trekking (blocks ~80-90% visible light); Category 4 for snow/glacier (blocks ~95%, too dark for driving but correct for high-altitude snow). UV400 rating is non-negotiable regardless of category. Polarized helps with glare but does not substitute for UV protection.
What is snow blindness and how do I avoid it?
Photokeratitis — a corneal sunburn from UV exposure that hits 6-12 hours after the exposure and temporarily blinds you. Painful, frightening, entirely preventable with proper sunglasses. The delayed onset means you feel fine during exposure; the burn arrives that evening.
Do I need glacier glasses or are regular sunglasses enough?
Wraparound or side-shielded — the critical feature is blocking UV around the frame edges; regular fashion sunglasses let UV in around the sides. Glacier glasses (Category 4, leather/plastic side shields) are the traditional and effective solution for snow travel. Category 3 wraparound is adequate for most trekking.
Should I buy sunglasses in Kathmandu or bring them?
Bring quality from home if you have them — Thamel shops sell fake Julbo/Ray-Ban alongside decent house brands; the UV400 claims on cheap lenses are unreliable. If buying in Kathmandu, inspect claims skeptically and spend more for the legitimate brand. A spare pair is essential — losing your only sunglasses at 5,000m is a medical problem.
