Is it normal for the outer rim of my irises to develop a grayish color?

The grayish color you see in the outer rim of your iris is actually in the cornea, the clear window of your eye, in front of the brown iris. Medically, it is called arcus senilis (in Latin) or gerontoxon (in Greek.) These whitish or grayish rings are common in old and even middle-aged human eyes. They are more obvious in brown eyes than in blue eyes. The ring is caused by cholesterol compounds that form in the peripheral cornea. However, the presence of such a ring is not an indicator of elevated blood cholesterol, and the ring causes no impairment of vision. No treatment is necessary or available.