Re: What triggers dark spots on the eye iris?

Hi Susanne,

Most people's eye color does not really change as you get older but can 
appear to change color because of various changes occurring in the iris or 
corneal physiology.  But in some conditions like Fuch's heterochromic 
iridocyclitis, one iris is a different color than the other and is often 
associated with glaucoma and iritis in the lighter iris.  Iris nevi are 
similar to freckles found on your skin but do not grow or change color and 
completely benign.  On the other hand, tumors of the iris are usually dark 
masses that can definitely change the color of your iris.  Another 
condition not found on the iris known as arcus senilis, can change the 
appearance of iris color to a lighter shade.  This is common in people 
over the age of 40 and is caused by lipid deposits in the cornea that 
appear as a hazy white ring around the iris.  
     I hope this helps!  

Kenton L. McWilliams, O.D.

taken from: The Wills Eye Manual, 2nd edition
            R. Douglas Cullom, Jr., M.D. and Benjamin Chang, M.D.