Another type of contact lens that you should know about is scleral lenses; these lenses were first manufactured in 1888. A scleral lens is a large-diameter gas permeable contact lens. The lens rests on the white part of the eye, also known as the sclera, and vaults over the entirety of the corneal surface. There is a gap between the contact lens and the cornea that is filled with fluid. And the earliest models were made of glass and after the development of polymethyl methacrylate or PMMA, developers were able to create a new lens with improved permeability of oxygen and it was easier to reproduce. This lens can also function as prosthetics for corneal tissue due to corneal irregularities, due to ocular trauma, surgery, or diseases.