The sphere of the eye has the lowest internal stress energy of geometric structure and even if a vitrectomy has been performed removing all the fluid the eye maintains most of it's original shape
The uterus keeps the trachea from collapsing in a fetal pig.
Its cytoplasm.
The eyeball is filled with a gel-like substance called vitreous humor that helps maintain its shape and structure. Additionally, the pressure inside the eye, known as intraocular pressure, also plays a role in preventing the eyeball from collapsing. The external layers of the eye, including the sclera (white part) and cornea, provide further support to keep the eyeball intact.
cytoplasm
hydrostatic
The sclerotic coat is a tough, white layer that surrounds the eyeball. Its function is to provide structural support and protection to the eye, maintaining its shape and preventing it from collapsing.
Dynamic equilibrium.
The trachea has a series of cartilage rings that prevent it from collapsing.
gravity maybe?
Like a camera has a case, the eye is surrounded by tissues and are filled with fluid called "humours" to keep it from collapsing.
Ragetti in Pirates of the Caribbean, curse of the black pearl.
conjunctiva