The test most frequently used for detecting ocular deviations is the Maddox rod test. It is easy, speedy and apparently accurate, though in some cases its accuracy is only apparent. It is very accurate for measuring hyperphoria, but it often shows less exophoria and more esophoria than the more reliable cover test.
I have seen a patient with 8 prism diopters of exophoria show as much as 30 prism diopters of esophoria when tested with the Maddox rod. It is not uncommon for a patient to say that the line seen by the eye through the Maddox rod seems to be nearer than the light—not simply right or left or up or down or slanting. This impression of nearness tends to make the patient accommodate, especially if the tendency to accommodate is easily excited, as in the foregoing instance ; then the associated tendency to convergence results in esophoria. If during
LANCASTER WB. DETECTING, MEASURING, PLOTTING AND INTERPRETING OCULAR DEVIATIONS. Arch Ophthalmol. 1939;22(5):867–880. doi:10.1001/archopht.1939.00860110153010
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