Measurement and diagnosis of cyclodeviation by the after-image method.

Lesions involving the vertical muscles or their nerve supply usually result in some degree of torsional deviation of the eye which may produce intractable and distressing asthenopia. Although cyclophoria has long been recognized and has been demonstrated with such apparatus as the Maddox rod, Maddox wing, Maddox double prism, and synoptophore, it is nevertheless frequently overlooked. Moreover these tests permit no definite conclusions to be drawn regarding the muscle at fault. A new method of diagnosing cyclodeviation of the eye with the help of the "after-image" test is described below. If it is carried out in three positions of gaze, namely looking straight forwards, looking up, and looking down, the muscle involved can be identified.