From the day they are born, every person has a certain amount of tension in their muscles, known as muscle tone, which is also present when the body is at rest. The natural movement of the muscles causes them to move to a greater or lesser degree, briefly forming wrinkles. The skin is capable of compensating for this pattern of tension and release for a very long time. However, with increasing age and decreasing skin elasticity, there comes a point at which these expression-related lines no longer disappear. They become deeper and are visible as eye wrinkles even when the facial muscles are relaxed.