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The scleral ring or sclerotic ring is a hardened ring of plates, often derived from bone, that is found in the eyes of many animals in several groups of vertebrates. Some species of mammals, amphibians, and crocodilians lack scleral rings. [1] The ring is in the fibrous outer layer of the eye, called the sclera.
A circle of bony plates, the sclerotic ring, surrounds the eye and holds it rigid, but an improvement over the reptilian eye, also found in mammals, is that the lens is pushed further forward, increasing the size of the image on the retina. [4] Fields of view for a pigeon and an owl
The sclera's blood vessels are mainly on the surface. Along with the vessels of the conjunctiva (which is a thin layer covering the sclera), those in the episclera render the inflamed eye bright red. [6] In many vertebrates, the sclera is reinforced with plates of cartilage or bone, together forming a circular structure called the sclerotic ring.
The skull of a normal bird usually weighs about 1% of the bird's total body weight. The eye occupies a considerable amount of the skull and is surrounded by a sclerotic eye-ring, a ring of tiny bones. This characteristic is also seen in their reptile cousins.
The diameter of the eye socket was 2.8 cm (1.1 in), while the outer diameter of the sclerotic ring was 2.3 cm (0.91 in), and its inner diameter 1.5 cm (0.59 in). The ring consisted of 15 ossicles (small bones also termed plates) which overlapped each other with no gaps, and the rims of the ring were regularly rounded.
Anhanguera had bony rings in their eye sockets, called sclerotic rings. These disks may have provided support to the pterosaur's eyes. Sclerotic rings are found in some extant species of vertebrates. [7] For example, modern day birds have sclerotic rings. [7]
Protoceratops skull with large sclerotic rings. Based on the size of its sclerotic ring, Protoceratops had an unusually large eye among protoceratopsids. In birds, a medium-sized sclerotic ring indicates that the animal is a predator, a large sclerotic ring indicates that it is nocturnal, and the largest ring size indicates it is a nocturnal ...
The skull of SAM-PK-5867. Some specimens of Euparkeria preserve bony rings in the eye sockets called sclerotic rings, which in life would have supported the eye.The sclerotic ring of Euparkeria is most similar to those of modern birds and reptiles that are nocturnal, suggesting that Euparkeria had a lifestyle adapted to low-light conditions.