retinal correspondence, abnormal (ARC)
A type of retinal correspondence in which the fovea of one eye is associated with an extrafoveal area of the other eye to give rise to a perception of a single object. This phenomenon is common in strabismus, but may also occur as a result of a macular lesion. ARC is often classified in three types: (1) Harmonious, in which the angle of anomaly is equal to the objective angle of deviation. This indicates that the ARC fully corresponds to the strabismus. (2) Unharmonious, in which the angle of anomaly is less than the objective angle of deviation. (3) Paradoxical, when the angle of anomaly is greater than the objective angle of deviation. ARC can be detected by examination with a major amblyoscope, with the after-image test, or by comparison between the objective and the subjective angles of deviation measured with the alternate cover test and either a Maddox rod or the von Graefe's test, respectively (a difference between the objective and the subjective angles indicates ARC) (Fig. R10). Syn. anomalous retinal correspondence; ret-inal incongruity. See incongruous diplopia; physi-ological diplopia; phi movement; after-image test; Bagolini's test.
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Fig. R10 Abnormal retinal correspondence between M′L and B′ in right esotropia (M′R, fovea of the right eye)
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