may I add my partner is 46 a little young for cornea arcus senilis maybe? it doesnt look like chorlestorol pictures either
looked at the web pictures, looks nothing like any of them, it looks like a cloud has passed over part of the iris, almost to the centre, it doesnt have a defined edge isnt in a ring shape or spotted and no colour shows through, his eyes are dark brown but in this area it is white.
It most likely is a cornea arcus. Usually due to age like hair graying. in younger individuals can be due to high blood choleserol. See an eye MD find one at www.aao.org
Use Google IMAGES and serach corneal arcus senilis to see if this is what it looks like.
JCH III MD