(physiology) The simultaneous turning of both eyes when focusing.
(optics) A measure of convergence or divergence of rays.
1947 Benjamin King Johnson, Optics and Optical Instruments: An Introduction with Special Reference to Practical Applications, Courier Corporation (1960 [1947]), p. 152.
"Ample movement between the source and condenser should be available in order to allow for a variation in the vergence of the light leaving the condenser"
(geology) The direction of the overturned component of an asymmetric fold.