A biomicroscopy contact glass features one fixed and one adjustable mirror. Mirror adjustments are made by turning an easily accessible knurled ring enveloping the lens housing. The main advantages are nonreversed fundus and anterior chamber imagery, and a meridional direction of scan. A built-in scale permits approximate indications of positions. The design minimizes microscope manipulations.
Friséen L. An Adjustable Biomicroscopy Contact Glass With Erect Imagery. Arch Ophthalmol. 1972;87(2):202-205. doi:10.1001/archopht.1972.01000020204017