Figure 3.

Illustration of volume scotomas due to binocular central scotomas under different fixation conditions (assuming equal scotomas centered on the fovea in each eye and inferior PRL). The thick line within the projected scotomas represents the direction of the visual axis. (a) When the eyes fixate at infinity, an anterior volume scotoma of constant angular extent equal to the angular size of the scotomas extends to infinity from the point at which the monocular scotomas begin to overlap (see Appendix Eq. A1). (b) When the convergence angle to fixation is equal to the angular scotoma size, an anterior volume scotoma is present (starting at the distance given in Appendix Eq. A2) along with a posterior tunnel scotoma (of constant linear size equal to the IPD) that extends to infinity. (c) When the convergence angle is greater than the scotoma size, a finite kite-shaped zone of volume scotoma with anterior (Eq. A2) and posterior (Eq. A3) limits is formed. The projected scotomas due the ONH physiological blind spots are shown. The scale is varied to include the interactions of the ONH and central scotomas. Scaling for 10° central scotomas and an IPD of 6.6cm is used in each case. Equations A4–A7 delimit these interactions. The scale differences may be appreciated by comparing the eye size and IPDs between the various images.