Diagnosis of an isolated vertical muscle palsy

The determination of a paretic vertical muscle may be made by prism cover test measurements in the 9 diagnostic positions of gaze or the 3-step test which relies on the Bielschowsky head tilt test. A series of cases with an isolated paretic vertical muscle was used to compare the 2 methods of examination. It was found that 1) the 3-step test (based on the Bielschowsky head tilt test) is non-diagnostic as frequently as fielding out, 2) the 3-step test is much more likely to diagnose an oblique (especially the superior oblique) than any other muscle, 3) there is a statistically significant association between a loger duration of the paresis and the appearance of spread of comitance, and 4) the disagreement between the 3-step test and cardinal gaze measurements which occurs in 18% of cases can not be adequately explained by 'overspread of comitance' to the point where the deviation is maximum in the opposite field of gaze. The measurement of the deviation in the cardinal positions of gaze was felt to more accurately indicate the paretic muscle when the two tests were in conflict.