If you see a dark outline around your iris -- the colored part of your eye -- this is your limbal ring. It is darkest when we are at our healthiest and naturally fades with age and poor health.

Iris Freckles a Potential Biomarker for Chronic Sun Damage. Investigative Opthalmology & Visual Science, 2017; 58 (6): BIO174 DOI: 10.1167/iovs.17-21751 ...