Indirect gonioscopes use mirrored surfaces to allow biomicroscopic examination of the anterior chamber angle. There are two main types: Goldmann and Zeiss. Goldmann lenses use solution (1% methylcellulose, celluvisc) to create a continuous optical interface between the eye and the lens. Goldmann types have one to four mirrors, which determine the degree of rotation necessary to examine the entire angle. Zeiss lenses don't need fluid because the contact surface is smaller and flatter. Four mirrors provide a 360 degree view with little rotation of the lens.