What causes the loss of iris pigment as you get older?

In most cases it is the beginning of cataracts. As the cataract forms, less and less of the iris is visible. Surgical correction is required, as the cataracts grow thicker, you loose your sight. But there are other reasons, and you should see an Ophthalmologist.

What causes the loss of iris pigment as you get older?
the same thing that cause loss of everything when you get older.

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