Barbara Marquand is a staff writer at NerdWallet, a personal finance website. Email: bmarquand@nerdwallet.com. Twitter: @barbaramarquand.
The eye may change color due to alteration of genes in the cells of the iris. This is because of your DNA factors in the body. The gene alteration can cause the eye to change color from brown to green and vise verse. There is no any explanation to the cause of the genes behaving in these manner. Prolonged exposure to the sun might also be another cause that made my eyes to change the color.
For instance, there are normal age-related changes in the pupils (less light can enter the eye), the eyes' accommodation speed decreases (it takes longer for eyes to transition to different light levels), and color perception weakens (yellowing of the lens makes it difficult to distinguish greens from blues).