The Tilt of the Lancaster Chart: An Indirect Qualitative and Probably Quantitative Sign of Cyclodeviation

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Diagnosis of torsion classically relies upon analysis of subjective tests (image tilting) and objective tests (fundus photography demonstrating the rotation of the optic disc). Unfortunately, discrepancy between the results of these different tests occurs. Following the von Noorden school's works, we know that sensorial adaptation to image tilting is the main reason for which we cannot rely on subjective answers in cyclodeviations. This study is based upon the fact that, since sensorial adaptation is unique to cyclodeviation, it should be possible to make an indirect diagnosis of cyclodeviation through the study of the vertical and horizontal disorders caused by the cyclorotations in the different diagnostic positions of gaze. Indeed a “spiraling” of the deviations around the primary position leading to a tilt of the synoptometer chart (objective testing) or of the Lancaster chart (subjective testing) is described.When coordimetry is feasable, observation of the tilt of the Lancaster gives an accurate if not perfect idea at a glance of the existence and of the degree of a cyclodeviation whatever it might be (ex***cyclo or in-cyclo) and whatever its origin. Further studies are still needed to establish to what extent the real anatomical degree of an eye cyclodeviation corresponds to the angle of tilt and on which meridian it should be measured.