IS THERE A TRUE PRIMARY AND SECONDARY DEV IATION IN 4TH CRANIAL NERVEPALSIES

Background An extraocular muscle palsy is conventionally characterized by a deviation of the visual axes, this being greater when measured w ith the affected eye fixing. By definition and illustrating Hering's l aw, this secondary angle of deviation is greater than the primary one, measured with the sound eye fixing. We present here a comparative stu dy of the amount of subjective excyclodeviation measured in patients s uffering from IVth nerve palsy, with the sound or affected eye fixing. Methods Two groups of patients were entred into the study : Group 1 ( N = 54) for superior oblique palsies studied retrospectively and Group 2 (N = 14), for a prospective study of those recently acquired (post- traumatic) and followed over 6 months. In both groups, measurements we re made at two stages, early (1 to 7 weeks after onset) and late (4 to 6 months later). Results In both groups, the majority of cases showed a greater secondary torsional deviation, the difference between this and the primary deviation lessening on late stage measurements. Conclu sion In both groups, the difference between primary and secondary tors ional deviation was not statistically significant.