K 551
Precision of Binocular 3D Videooculography (B3D-VOG)
K. H. Wassill, H. Kaufmann
Introduction: The prism-cover-test measures the position of one eye relative to that of the other. Videooculography detects ocular positions in relation to a frame of reference, which is supported by the head itself and which corresponds exactly to the videomask. Rotational positions are determined using an overlay procedure of prominent iris landmarks.
Squint is the computed difference in three dimensions between both eyes and should show the same amount as the fusioned prism.
Methods: Fusion measurements took place both with prisms of increasing and decreasing strength, and also using a randomised order, moving towards the physiological limits of fusional capability. When using a chin rest, movements of the head are identical with the movements of the non-fusioning eye. Thus no bite board is necessary.
Results: Using an artificial fixed eye, the maximum resolution which can be achieved using videoculography, lies in the pixel range of 0,01 degrees. Physiological movements such as microsaccades cause a standard deviation of 0.18 in the horizontal, 0,8 in the vertical and 0,9 in the torsional planes, as is shown in the small table below.
|
Nr. |
1 |
2 |
3 |
4 |
5 |
6 |
7 |
8 |
9 |
10 |
|
Pprism=6° |
6,0 |
6,0 |
6,1 |
5,9 |
5,8 |
5,8 |
5,6 |
5,7 |
5,8 |
5,5 |
95% of all measured values lie within in the 2 sigma interval of confidence. This precision was reached within a tested field of gaze measuring 18 degrees in diameter. The randomized procedures avoided the effects of anticipation or hindsight which can be observed when using a linear increase or decrease in prism rows. As the rotation of a hand held prism around the line of sight can lead to deviations in the horizontal and vertical portions, the prism was mounted in a stable position. Within B3D-VOG, primary, secondary and tertiary positions are subject to the same standard deviations, which is interpreted as a lack of false torsion.
Discussion: The precision of the binocular videooculography is sufficient. It would be desirable to use a larger field of observation.
Supported by Deutsche Forschungsgemeinschaft Nr: 1366/1-1 030/98
Augenklinik für Schielbehandlung und Neuroophthalmologie der Justus-Liebig-Universität, Friedrichstr. 16, D- 35392 Giessen