Ophthalmic Calipers and surgical eye calipers are used to measure the muscles of the eye, joints, and small bones. Features include straight or curved tips and titanium versions. There are straight, ruler-style calipers such as the Braunstein and the square Stahl, in addition spring-secured spreadable calipers such as Castroviejo, Goniometric, and Pearce, and internal measuring calipers such as the Osher.