From: The zone of comfort: Predicting visual discomfort with stereo displays Journal of Vision. 2011;11(8):11. doi:10.1167/11.8.11 Figure Legend: Vergence and focal distance in various viewing situations. The three columns on the left represent natural viewing (N), natural viewing with optical correction (G), and stereo 3D viewing (S). In natural viewing, the vergence stimulus and focal stimulus are always at the same distance and, therefore, are consistent with one another. In natural viewing with an optical correction for refractive error (spectacles or contact lenses), the focal distance is different from the vergence distance because of the constant decrement or increment in focal power due to the correction. Stereo viewing creates inconsistencies between vergence and focal distances because the vergence distance varies depending on the image contents while the focal distance remains constant. The right side of the figure plots focal distance in diopters as a function of vergence distance in diopters for the six viewing conditions schematized on the left side. The green line represents natural viewing, the blue line represents natural viewing with an optical correction, and the red line represents viewing a stereo display. Near and far distances are indicated on the axes. Date of download: 11/7/2017 The Association for Research in Vision and Ophthalmology Copyright © 2017. All rights reserved.