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I've had my Tifosi sport glasses with photochromic lenses for about 4 years. Lately, when I rode them in 10 am morning sun, my eyebrow and eye started to feel terrible pain, that passed once I removed my sunglasses. A friend of mine, that works in a bike shop said that polycarbonate lenses have a life span of about 3 years. I've bought a new pair of glasses, but now I'm trying to decide what to do with the old pair. So the question, do polycarbonate lenses really degrade with wear, time and when wiping them?

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    In your narrative, it’s unclear why you felt pain. Do you think the photochromic layer of the lens wore through and you got sunburn of the retina (which can happen). Or did the lens physically break and poke you in the eye? – RoboKaren Oct 13 '17 at 13:32
  • Pardon for a long story :-) The lenses are physically OK, but it felt to me like they stopped to have the desired optical characteristic (reducing the sunlight), so I was forced to frown which lead to pain. – J-unior Oct 13 '17 at 14:30
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    Some lazy Googling suggests 3 years for photo-chromatic lenses. Are they at all discoloured when clear? – alex Oct 13 '17 at 15:11
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    As an aside, I tend to destroy the frames long before the lenses. Sunscreen and sweat rotted the rubber on a pair, sweat corroded the magnesium on another... – alex Oct 13 '17 at 15:13
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    Polycarbonate is though and doesn't break, but it scratches easily. You can't wipe the lenses with everything that comes at hand. – Cristian Ciupitu Oct 15 '17 at 0:49
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Sunglasses have two enemies: dirt and UV rays.

The polycarbonate itself is fairly tough and can last over ten years. It’s likely to get scratched up before the UV starts to cause it to yellow or ‘craze.’ The coatings are more delicate. The anti reflective coatings are easily scratched especially if you use your sweat and dirt soaked jersey to 'clean' them.

The photochromic layer itself is activated by UV light but is also damaged by it. Generally, one can expect photochromic lenses to last 1-3 years depending on use. Keeping the sunglasses in a case (and away from UV rays) when not using them helps protect them.

  • One can partially "re-awaken" self-darkening lenses by leaving them in the freezer overnight. Or the refrigerator overnight works okay too. – Criggie Oct 18 '17 at 9:25

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