[Superior oblique muscle paralysis and ocular torsion. What is the effect of measuring method on the results?].

BACKGROUND: The rotation of the eye-ball around Fick's Y-axis is called ocular torsion. A precise measurement of the torsional deviation can be clinically as critical in the diagnosis of some complex strabological disorders as in the assessment of some systemic diseases.

MATERIALS AND METHODS: We measured the ocular torsion under binocular conditions by five measurement devices on 50 patients with superior oblique palsy. The comparison of the devices was performed using rank tests (Friedman, Wilcoxon signed rank).

RESULTS: The 5 methods of measurement do not produce equivalent results. These findings confirm on a population of paretic patients similar published results obtained with healthy subjects.

CONCLUSIONS: The simple Maddox rod and the synoptophore are among the most widely used methods to measure cyclotropia; this study reveals that these devices are the least reliable. Harm's tangent scale gives the most reliable results, in all directions of gaze; however, in inferior adduction, the synoptometer also yields a satisfactory measure of ocular torsion. In primary position, the double Maddox glass appears to be the most suitable instrument.