Limbal ring

[1] It is a dark-colored manifestation of the corneal limbus resulting from optical properties of the region.

[2] The appearance and visibility of the limbal ring can be negatively affected by a variety of medical conditions concerning the peripheral cornea.

[3] It has been suggested that limbal ring thickness may correlate with health or youthfulness and may contribute to facial attractiveness.

[1] Both health and youth are positively correlated with a prominent limbal ring.

[6] Furthermore, limbal rings appear to be most noticeable "for individuals relatively free from chronic health issues".