Iris (Definition) The iris is a structure within the eye that helps reduce the amount of light that reaches the retina. The iris is known as the colored part of the eye, and can be blue, brown, or any color or combination of colors in between. The iris is the portion of the eye that responds to light stimulation. ...Read more.
Scientists also speculate that caffeine may provide a mood-boosting effect that helps ease pain. Regardless of the mechanism by which it works, the data does indicate that caffeine does indeed make pain medications more effective and help ease pain.
The effects of caffeine are complex. I recall reading some studies that found that caffeine consumption associated with tea or coffee drinking was associated with lower rates of depression. But it is also true that heavy caffeine use can be tied to anxiety and insomnia, which could be connected to depression.