Two formulas are presented which permit rapid determination of accommodative and convergence demands in a Brewster stereoscope. The formulas are easily applied and are valid for any circumstances. The formula for convergence is unique in that it is independent of the patient's interpupillary setting for all instrument settings and yields results directly comparable to standard clinicat measurements. The formula for accommodation is:A = 1/TD - PThe formula for convergence is:C = (P × LS) - TS/ TDThest formulas hold where A is accommodation in diopters, C is convergence in prism diopters, TD is distance of stereogram from stereoscope lenses in meters, P is power of stereoscope lenses in diopters, LS is separation of optical centers of stereoscope lenses in centimeters, and TS is he separation of corresponding points of the stereogram half-views in centimeters.