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To the Editor:
—Convergence is a binocular function, as there can be no convergence in a one-eyed person. The angle formed by the two visual axes at the point of fixation is the (static) angle of convergence. It would therefore seem logical to define the unit of convergence, the meter angle, in a binocular sense. This has now been brought about by the recent decision of the Committee on Optics of the American Academy of Ophthalmology. They define the meter angle as the angle formed by the two visual axes at a point of fixation 1 meter from the center of the interocular base line.The original definition of Nagel used one visual axis as the measuring line; that is, the point of fixation was 1 meter away as measured on the visual axis. Use of the midline, that is, the line from the midpoint of the interocular base line
Pascal JI. A PHYSIOLOGICAL UNIT OF CONVERGENCE. AMA Arch Ophthalmol. 1955;53(4):616. doi:10.1001/archopht.1955.00930010624029