HETEROPHORIAS

Abstract
Many new tests for heterophorias have been described by as many different authors. All of them, however, are much alike in that no new fundamental principles have been introduced. Since von Graefe1described his diplopia test for excess of divergence, in 1857, many others have used minor variations of it. This type of test depends on the suspension of the fusion sense by creating an insurmountable diplopia in one meridian and by measuring the manifest phoria in the opposite meridian. The other type of test, of which the Maddox rod test is the best example, depends on a similar suspension of the fusion sense by producing so much distortion of one of the images that fusion is practically impossible. The manifest deviation can then be measured by prisms. In 1886, Stevens2emphasized the importance of heterophorias and gave his widely used classification of the different types. He early

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