These are the lines one gets around the outward corner of their eyes when they squint, smile, etc. As one ages, these lines become wrinkles, and are visible even if the skin isn't being smooshed.

This is one of the first signs of your skin aging, along with lines around the mouth. This is because the skin around the eyes is thinner, and doesn't have the same glands as the rest of your face.

The only way to avoid these is prevention, after they appear they will only go away with very drastic measures like Botox.