Comparisons of commercially available devices for the measurement of fixation disparity and associated phorias.

Associated phorias were measured on 89 subjects using various commercially available devices to compare the results obtained with them. An additional 14 persons served as subjects to compare fixation disparity curve parameters obtained with two different targets. Distance associated phorias using the Mallett unit and the American Optical vectographic slide were not significantly different. Nearpoint associated phorias using the Bernell unit and the Borish card were not significantly different. Associated phorias obtained with the Bernell unit and the Borish card were lower in magnitude than the associated phorias (x-intercepts) from fixation disparity curves derived using the Sheedy disparometer. Fixation disparity curve parameters using the Wesson fixation disparity card differ from those obtained with the Sheedy disparometer. Subjective comments on the clinical use of each of these instruments are included.