Hess Lancaster screen test with the head tilted: a useful test in the diagnosis of bilateral fourth nerve palsies.

PURPOSE To introduce Hess Lancaster screen test performed with the head tilted as a new ancillary test to help in the diagnosis of bilateral superior oblique (SO) nerve paresis. METHODS Three patients with clinical diagnosis of acquired bilateral fourth nerve paresis, three with clinical diagnosis of acquired unilateral fourth nerve paresis, and three normal subjects were tested with Hess Lancaster test in the nine positions of gaze with their heads straight and with their heads tilted to each side. Test results were compared and data were analyzed. RESULTS Hess Lancaster test of all patients with bilateral SO palsy performed with their heads straight showed unilateral SO underaction, but when the test was carried out with the head tilted to each side findings were positive for ipsilateral SO underaction and ipsilateral hypertropia for both sides. In those patients with unilateral SO palsy, Lancaster test was positive for SO underaction when the head was in straight position and when it was tilted to the side of the paretic muscle, but it was almost normal with the head tilted to the opposite side. Normal subjects did not show any abnormality regardless of the head position. CONCLUSIONS Bilateral SO palsies are sometimes difficult to diagnose for they might be masked. Hess Lancaster test carried out with the head tilted to both sides could help in the diagnosis of bilateral SO palsies.