n :  a transparent cylindrical glass rod or one of a series of such rods placed one above another for use in testing the eyes for heterophoria
 
Maddox, Ernest Edmund (1860-1933), British ophthalmologist. Maddox did research on refraction, ocular muscles, and the relation between accommodation and convergence. In 1898 he devised an instrument, consisting of parallel cylindrical glass rods (now called Maddox rods), for testing and measuring the degree of heterophoria.
 
 
 
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