To the Editor:
—Lieutenant Colonel Byrnes's comments in the December issue of the Archives on my article on the "Parallactic Angle in Binocular Depth Perception" (Arch. Ophth.28: 258 [Aug.] 1942) bring to the fore the want of clearcut definitions of some of the terms used. To start from the beginning, just what is meant by "binocular parallax"? If one consults the two leading medical dictionaries one finds the following definitions : Gould's medical dictionary says, "Binocular parallax is the angle of convergence of the visual axes" ; Dorland's "American Illustrated Medical Dictionary" says "Binocular parallax is the seeming difference in position of an object as seen separately by one eye and then by the other, the head remaining stationary." Different dictionaries are expected to define the same term in somewhat different ways but to convey the same meaning. These two definitions do not convey the same meaning. Furthermore, the term "binocular
Pascal JI. PARALLACTIC ANGLE. Arch Ophthalmol. 1943;29(2):313–315. doi:10.1001/archopht.1943.00880140161016
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