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E. S. Hald, D. Yang, R. W. Hertle; Clinical Application of a Digital Head Posture Measuring System. Invest. Ophthalmol. Vis. Sci. 2008;49(13):756. doi: https://doi.org/.
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We have developed a digital head posture measuring system (DHP) and reported the validity tested with an artificial head in some 3D positions previously.1 Now, we will report the repeatibility and accuracy of measurements performed in normal human subjects and in all possible 3D head positions, with application for clinical use in mind.
The DHP prototype consists of a head-mounted electronic compass, a standard PC, and customized software to sample and display 3D head posture in real time.The DHP and a mechanical head posture system (MHP) were mounted on a helmet.2 Using the MHP as a reference, human subjects positioned their heads at one of eight positions ranging from -30 to 30 degrees of simultanious yaw, pitch, and roll. The digital outputs of the DHP were recorded as soon as the head was in position. Three tests were performed on each subject and data from 12 subjects were used to calculate repeatibility of the measurements.
The DHP showed consistent outcomes compared with the MHD. For all angles and directions, yaw and pitch experimental measures had 95% limit of agreement angles that fell between a lower maximum angle of -5.25 degrees and an upper maximum angle of 6.60 degrees. For roll measurements, the 95% limit of agreement angles were slightly larger (lower maximum angle of -10.70 degrees, upper maximum angle of 8.85 degrees), but showed greater dependence on the size of angle being measured (10-30 degrees). As the angle being measured decreased, the limit of agreement angles also decreased. Data also showed the relative accuracy of the device. For all three directions of movement, the average output angle was lower than the actual angle (0.5-8 degrees), with increased difference between output and actual measures coinciding with increased size of actual angle.Discussion and
The repeatibility and accuracy of the measurements with DHP was supportive for the future use of the DHP on patients. With additional offline compensation made for the measurements, the DHP will be a valid device to repeatably measure head posture in 3D.References: 1. Yang D-S, Hald ES and Hertle RW. AAPOS 2007. 2. Yang D-S, Hertle RW, et al. Am J Ophthalmol. 2005 Apr; 139 (4):716-8.
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