Re: What would cause a male to have one eye of two differnt colors.

S. Williams,

     I am not aware of the terminology of "flex" or "sans flex". In answer 
to your question, you can have an iris of an eye with two different 
colors.  Some situations where this might occur, a person has a naevus 
(mole) on the iris that is a different color than the rest of the iris, 
ie: blue colored iris with a brown naevus.  Anytime a new naevus is 
noticed, you should get it checked out because of possibility of iris 
tumor or melanoma.  Some people with very light colored eyes have a ring 
of darker pigment around the pupillary ruff (inner area surrounding the 
pupil) that is noticed under biomicroscopy.  It is usually a benign 
phenomena.  A condition called Fuch's heterchromic iridocyclitis occurs in 
some people in which one iris may be brown and the other green.  It is 
usually associated with other conditions.  The color of one's iris is  
determined gentically except in the later two situations, and brown is 
dominant over green or blue.  Just like the color of human skin, eye color 
also is determined by how much pigment is in the cells that make up the 
iris epithelium.  I hope this answers your question.

K. McWilliams, O.D.