True scleral ring (eye ring bone)

The scleral ring is a bony ring in the eye of birds, some reptiles (e.g. iguanas), extinct dinosaurs, pterosaurs and ichthyosaurs. It consists of 14–15 overlapping or fused bony plates embedded in the sclera at the junction with the cornea.

This ring lies behind the iris and in front of the lens, without contact with other bones. Since the iris is attached to the scleral ring, its central hole determines the maximum pupil size. The scleral ring supports the eyeball and serves as an attachment point for the accommodation apparatus.

The shape of the scleral ring varies: in Galliformes it is flat, while in owls it is tubular, which improves their vision in the dark. Such differences provide valuable clues for the reconstruction of extinct species.

Specifications:
contains about 55 scleral ring (eye ring bone)