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F.H. M. Träisk, R. Bolzani, J. Ygge; A Comparison Between the Magnetic Scleral Search Coil and Infrared Reflection Methods for Saccadic Eye Movement Analysis . Invest. Ophthalmol. Vis. Sci. 2005;46(13):2914.
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Purpose: Main sequence analysis of saccadic eye movements has been performed in patients with different neurological and orbital diseases e.g. thyroid associated ophthalmopathy (TAO). The findings in TAO patients include subtle saccadic main sequence differences compared to normal subjects. The saccadic performance has mostly been evaluated using the magnetic scleral search coil system (MSC) due to the high quality of such recordings. However, the MSC method has a drawback in being invasive, which may limit its scope for use as a standard clinical tool. Another eye–tracking system, the infrared (IR) system does not have the same problem. Recent developments of this technique have not yet been tested for detailed saccadic analysis. Methods: Ten normal subjects performed horizontal and vertical saccades recorded with both methods. Eight recordings were complete and analysed for the maximum peak velocity (VMAX) and constant (C) of the main sequence curve. Results: . The IR recordings showed significantly higher peak velocity values compared to the MSC system and generally more inter–individual variability. No significant difference regarding peak velocity was detected between abducting and adducting saccades or between upward and downward saccades with either of the systems. Horizontal saccades showed higher peak velocities compared to vertical saccades measured with both techniques. Conclusions: Comparison of the main sequence plots of the IR and MSC eye tracking techniques reveals that the IR system yields higher values of VMAX and C. The relatively lower maximum velocity of the MSC recordings may have different explanations, e.g. slipping of the coil annulus on the surface of the eye and a possible change of the oculomotor command signal, induced by wearing the coil. Also, artifacts associated with the IR recording system may cause overestimations of the saccadic velocity and furthermore contribute to the higher variability of the IR recordings. Studies on the intra–individual variability in saccadic performance of normal subjects and comparisons between normal subjects and patients with TAO are in progress.
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