Determining the convergence demand for a patient who reads at a close working distance

Low vision practitioners frequently prescribe microscopic spectacles for reading. Although the lens power enables the patient to focus clearly, the convergence demand at the close working distance may make it difficult for the patient to achieve and sustain binocular vision. Base-in prism and lens decentration can reduce the convergence demand but even these methods are not always sufficient to achieve the goal of binocular vision. A means of calculating the convergence demand for a patient who is using microscopic spectacles of known parameters is presented as an aid to understanding the dynamics involved in achieving binocularity.