Wearing sunglasses physically protects the eye area, thus reducing the effects of sun damage on your eyes. But how can eye damage cause wrinkles?
The sun directly damages the eyes through UV exposure. UV rays strike the eye, accelerating the rate of cataract formation and worsening macular degeneration. It's your body's natural defense mechanism to squint the eyes to reduce the impact of UV exposure. In turn, constantly squinting from bright light can cause crows feet and other wrinkling around the eye area. Over time, the lines get deeper and the amounts of fine lines and wrinkles increase. Also, squinting to better focus your eyes can increase eye wrinkles over time - be sure to get your vision checked regularly.
How do you prevent squinting? It's an uncontrollable reflex, so you should wear sunglasses with UV protection and wear a hat. Most importantly, choose lenses with UVA/UVB protection. The FDA recommends selecting sunglasses with 99-100% UVA/UVB protection - the sticker on the lens will tell you what the coverage is. You can also select larger or wrap-around-glasses for more physical protection from the sun's rays on your skin, but this won't help much with squinting your eyes. People with lighter eyes or bigger pupils are more sensitive to light and may be prone to more squinting, so choosing a polarized lens that reduces glare may be a good choice.