RELATIVE ORIENTATION OF PRIMARY POSITIONS OF THE 2 EYES

We evaluated the relative orientations of the displacement planes of t he two eyes under various conditions: fixations of nearby targets, of far targets and targets presented dichoptically at optical infinity. W e show that disparity driven vergence is not always required to rotate the primary positions. We find that eye orientation during fixation o f far targets is idiosyncratic. We found a bimodal distribution rangin g from null to about 30 deg of the relative exorotations of the two pr imary positions. By contrast, the difference of primary positions' ori entation of the two eyes was, for targets at optical infinity, stable and similar across subjects. However, the displacement planes of the t wo eyes did not coincide, but were exorotated by 4.3 deg on average, e ven though horizontal vergence was close to zero. We discuss our resul ts with reference to current models of binocular three-dimensional con trol. (C) 1997 Elsevier Science Ltd. All rights reserved,