eye cap
/ˈʌɪ kap/noun
1Any of various types of part attached to the end of the eyepiece of an optical instrument; specifically (a) a tubular attachment which alters the image that the viewer sees, or which makes viewing more comfortable; (b) a protective cap for the eye lens.
2 Entomology. In some small moths: an expanded basal segment of the antenna which partly covers the eye.
3In embalming and funeral practice: a device inserted under the eyelids to maintain the shape of the eyeball and keep the eyelids closed.
4 Zoology. The (usually transparent) scale that covers the eye in snakes and certain other reptiles.
Origin
Early 19th century. From eye + cap.