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JE Ygge, R Bolzani, M Benassi; A New Way Of Finding The Primary Position Using Three Dimensional Eye Movement Recordings . Invest. Ophthalmol. Vis. Sci. 2002;43(13):2649.
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Purpose:To set up and evaluate a new and easy method for estimation of the ocular primary position (PP) based on two-dimensional fitting curves. Methods:A three dimensional scleral search coil system (Skalar Inc.) was used to record the eye position in ten normal subjects while performing a saccadic paradigm. The stimulus target, a red spot on a dark screen at 1.5 meter from the subject, moved from the centre position to 20° left-down, 20° right-up, centre, 20° right-down, 20° left-up. Thus the eyes performed an X-shaped movement which was analysed off-line by computer software. Using a polynomial fitting function the PP, in the Listing sense, was evaluated as well as the goodness of fit coefficient. Results:The method allowed us to estimate the PP for all subjects. Using the found PP as an origin for horizontal and vertical rotation, the theoretical torsion angle was evaluated by means of the Listing formula (Robinson, 1975). The comparison between the theoretical and the measured torsion showed a good agreement in XY graph and correlation coefficients close to 0.9. Conclusion:Using the method proposed in this study, which applies fitting function to the recorded data, the PP coordinates are easely obtained in a graphical way. Moreover, the reliability obtained by this method depends on the number of recorded points. Even analysing only a single movement in the two main diagonals is sufficient to evaluate the PP, but having many repetitions of the diagonal movements would perform a better fitting coefficient. Reference: Robinson D A (1975). A quantitative analysis of extraocular muscle cooperation and squint. Invest. Ophthalmol., 14, 11, 801-825.
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