In the June, 1932, issue of the Archives, Dr. Lloyd1 stated that in a series of three hundred patients 6 per cent had binocular vision for distance but not for near, as shown by their inability to pass the BishopHarman diaphragm test. In answer to my inquiry he stated that he proved the distance stereoscopy by the fact that "with the stereoscope they could fuse all degrees of the Wells charts." This must have included depth perception. With the charts heretofore available for the BishopHarman test, it was impossible to test depth perception, as he stated, so that failure must mean inability to name the letters YDRAHAF in correct sequence, second degree fusion.
Since reading Dr. Lloyd's statement I have been testing with the Bishop-Harman test all patients who could fuse the stereoscopic charts, and have not found one who could not name the letters in
Wells DW. DEPTH PERCEPTION WITH THE BISHOP-HARMAN DIAPHRAGM TEST. Arch Ophthalmol. 1933;9(3):450–452. doi:10.1001/archopht.1933.00830010466011
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