There is no way to tell for sure but the most common cause would be a corneal arcus. This is an aging change in the peripheral retina. If your age is 42 it can be associated with high blood levels of cholesterol.
You need to see an Eye MD ophthalmologist for a definitive diagnosis. you should have your personal physician do a "fasting lipid profile" if you have not had that test in the last 2 years.
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