[Study of optic nerve head-fovea angle with retinophotography in congenital fourth nerve palsy].

PURPOSE: Measurement of ocular torsion is an important element for analysis of certain oculomotor pathologies such as fourth nerve palsy. With nonmydriatic retinography, objective measurements of ocular torsion are now accessible in daily practice: the normal values in healthy subjects are known. We compared a population of subjects with fourth nerve palsy to a reference population.

PATIENTS AND METHODS: Prospective study of 38 cases of congenital fourth nerve palsy, who had never undergone surgery. Each of these subjects had nonmydriatic retinography done according to a standardized protocol. The ocular torsion was measured using graphic software with consideration of reproducible anatomical marks. A statistical study determined the thresholds of significance.

RESULTS: In this pathological population, the angle between the optic nerve head and fovea is organized in a Gaussian distribution but the values are different from those found with the same method in a population of healthy subjects (6.3 degrees +/-3.4) (t test, p<0.0001). Extorsion exists in paralytic eyes (mean, 10.7 degrees +/-3.8), as in the other eye (mean, 8.8 degrees +/-5.7). In addition, the study of the anatomical marks of the fundus (optic nerve head and the lower pole of the papilla) was shown to be reliable.

DISCUSSION: This study confirms ocular torsion's variation in fourth nerve palsy. Extortion was found in both eyes. We demonstrated no relation between the severity of the extortion and the lateralization of the fixating eye. We confirmed the results of previous studies.

CONCLUSION: This study confirms the relevance of the objective measures of the ocular torsion in a pathological situation. Simple anatomical marks of eye fundus provide a useful analysis of these clinical presentations.