Thank you for the insight. One update -- that link now seems to be something else. Google returns this link when you search the term Corneal Arcus. (Dropped the leading A).
http://classes.kumc.edu/som/aamc/icm851/images/photoimages/page54_80.htm
If the circle is on the cornea then it's a arcus of the cornea. If you have not had your blood fats (Lipids=cholesterol, triglycerides) checked you should have a "fasting blood lipid" test drawn and discuss it with your physician. The grey material is cholesterol being deposited in one of the layers of the cornea. It never threatens sight but it can be a sign of high blood fats.
After 60 its considered a normal part of aging like the hair turning gray.
Paste this link in your internet brower to see A CORNEAL ARCUS:
http://content.revolutionhealth.com/contentimages/images-image_popup-ans7_arcus_senilis.jpg
jch iii md