This thesis presents the results of oculomotor recordings obtained with a new type of scleral induction coil with which horizontal, vertical and torsional eye movements were measured simultaneously. In Chapter II, the stability of gaze in these three dimensions was measured in eight emmetropic observers. Subjects held the head still or oscillated it at 0.16~0.67 Hz (amplitude about 10 deg) in the horizontal, vertical or torsional plane while fixating a point target at optical infinity. Veridical gaze and head coordinates were calculated with full correction for non-linear goniometric relations and for cross-coupling artifacts due to misalignments of the coil on the eye. The amount of gaze instability in the horizontal and vertical direction was virtually identical. With the head still, in either of these directions the mean standard deviation of gaze position (inclusive saccades) was about 7 min arc; mean non-saccadic retinal image speeds were 20-30 min arcjsec. During head oscillation these values increased to about 16 min arc and 1 deg/sec; a mean of about 2.5% of the head motion remained uncorrected by the compensatory eye movements. Gaze stability in the torsional plane was considerably inferior to that in the horizontal and vertical plane. With the head held still, the mean S.D. position was about 17 min arc; (short-term drift) of torsional gaze mean torsional non-saccadic retinal image speed was about 46 min arcjsec. Long-term drift, expressed as the S.D. of the mean of torsional gaze position in consecutive zero position measurements, was 2.14 deg. Gain of the torsional compensatory eye movements was frequency dependent and rose from about 0.26 in static conditions (0 HZ') tO~-:about 0.42 at 0.16 Hz and 0.64 at 0.67 Hz. The validity of Listing's law was reinvestigated in Chapter III by means of a direct test. Either eye of 4 subjects was measured monocularly. Eye positions were measured in Fick coordinates and ocular torsion values were compared to the theoretical ones predicted by Listing's law. During consecutive measurements in the primary position torsion values were close to zero although considerable fluctuations of torsion were seen. Short-term drift was about 8' min arc and long-term drift about 1.64 deg. Torsion values in the secondary positions were also close to zero. In the tertiary positions torsion in the direction as predicted by Listing's law and increasing with eccentricity was recorded. In the temporal quadrants mean torsion was quantitatively in agreement with Listing's law; torsion values in the nasal quadrants however showed systematically larger values and this discrepancy increased with eccentricity to more than 50%. Statistical support for this finding however, was seen only in 4 out of 8 eyes. Symmetry could be obtained by shifting the chosen horizontal primary position (gaze parallel to the midplane) in the temporal direction; as a consequence all measured torsion ·values would exceed the ones specified by Listing's law. Torsion values varied idiosyncratically among subjects and among the left and right eyes of any one subject. It is concluded that Listing's law specifies ocular torsion only approximately: physiological eye movements show considerable stochastical as well as systematical deviations from this law.

eye movements, head movements, ocular orientation, optokinetic reflexes, vestibulo-ocular reflexes
H. Collewijn (Han)
Erasmus University Rotterdam
These investigations were supported by the Foundation for Medical Research MEDIGON (grant nr: 900-550-92).
Erasmus MC: University Medical Center Rotterdam

Ferman, F. (1987, September 30). Ocular orientation during head and eye movements : an evaluation with a three dimensional scleral induction coil technique. Erasmus University Rotterdam. Retrieved from