The structure is commonly referred to as the sclerotic ring; but, because the word sclerotic often implies pathology of the sclera (see "sclerosis", an unrelated medical condition[2]), recent authors have urged avoiding the use of this term, to avoid confusion and to increase the utility of character comparisons.
[1] Fossil scleral rings are known for a variety of extinct animals, including ichthyosaurs, pterosaurs, and non-avian dinosaurs,[4][5] but are often not preserved.
[2] Additionally, scleral rings may help the eye adjust to different viewing distances, also known as visual accommodation.
Fossil evidence shows that extinct marine crocodiles living in the Mesozoic had scleral rings, so the trait was lost over time.
[6] Scleral rings of varying lengths, curvatures, numbers of ossicles, and thickness are found in all birds.