Analytical aids for determining induced vertical prism imbalances in anisometropia

Anisometropes may experience considerable discomfort as a consequence of the vertical prismatic imbalance induced in their correcting lenses. Many patients successfully adapt. Where difficulties continue to be experienced, the prescription must include some degree of compensation. When the patient's correction involves cylinder, determination of the induced imbalance frequently proves to be tedious. For the clinician who wishes to calculate the induced imbalance before determining the required compensation, three useful methods have been developed and are presented in this paper. After a brief discussion of the problem, the three analytical aids are detailed, with examples, followed by their derivation and analysis.