Static and dynamic components of ocular counterroll as well as cyclorotatory optokinetic nystagmus were measured with a scleral search coil technique. Static counterroll compensated for about 10% of head roll when the head was tilted to steady positions up to 20 deg from the upright position. The dynamic component of counterroll, which occurs only while the head is moving, is much larger. It consists of smooth compensatory cyclorotation opposite to the head rotation, interrupted frequently by saccades moving in the same direction as the head. During voluntary sinusoidal head roll, cyclorotation compensated from 40% to more than 70% of the head motion. In the range 0.16 to 1.33 Hz, gain increased with frequency and with the amount of visual information. The lowest values were found in darkness. The gain increased in the presence of a visual fixation point and a further rise was induced by a structured visual pattern. Resetting saccades were made more frequently in the dark than in the light. These saccades were somewhat slower than typical horizontal saccades. Cyclorotatory optokinetic nystagmus could be induced by a patterned disk rotating around the visual axis. It was highly variable even within a same subject and had in general a very low gain (mean value about 0.03 for stimulus velocities up to 30 deg/s). It is concluded that cyclorotational slip velocity on the retina is considerably reduced by counterroll during roll of the head, although the residual cyclorotation after the head has reached a steady position is very small.

Human ocular counterroll: assessment of static and dynamic properties from electromagnetic scleral coil recordings.

Binocular eye orientation during fixations: Listing's law extended to include eye vergence

Purpose: To determine whether cyclotorsion occurs when a subject changes from binocular to monocular fixation and to assess positionally induced cyclotorsion. Setting: Clinics of the Rotterdam Eye Hospital, Rotterdam, The Netherlands. Methods: The axis of astigmatism was measured with the Nidek handheld keratometer in 15 normal subjects under monocular and binocular fixation and in seated and supine positions. The limits of agreement for the repeatability of measurements with the Nidek keratometer were used to identify subjects with statistically significant cyclotorsion. Results: Two subjects (13%) showed statistically significant excyclotorsion when changing from binocular to monocular fixation in a seated position. In a supine position, 3 subjects (20%) showed excyclotorsion when the fixation changed. Body position itself had no influence on ocular torsion. Conclusions: Significant cyclotorsion may occur under monocular viewing conditions. If monocular photorefractive keratectomy procedures are based on binocular keratometry readings, an undercorrection of myopic astigmatism may result. Individuals at risk should be identified before refractive keratectomy is performed.

Cyclotorsion: a possible cause of residual astigmatism in refractive surgery.

To achieve stereoscopic vision, the brain must search for corresponding image features on the two retinas. As long as the eyes stay still, corresponding features are confined to narrow bands called epipolar lines. But when the eyes change position, the epipolar lines migrate on the retinas. To find the matching features, the brain must either search different retinal bands depending on current eye position, or search retina-fixed zones that are large enough to cover all usual locations of the epipolar lines. Here we show, using a new type of stereogram in which the depth image vanishes at certain gaze elevations, that the search zones are retina-fixed. This being the case, motor control acquires a crucial function in depth vision: we show that the eyes twist about their lines of sight in a way that reduces the motion of the epipolar lines, allowing stereopsis to get by with smaller search zones and thereby lightening its computational load.

The motor side of depth vision.

https://repub.eur.nl/pub/65071/REPUB_65071_OA.pdf

Instability of ocular torsion during fixation: cyclovergence is more stable than cycloversion

Fusional cyclovergence was demonstrated for the first time, using ab objective photographic method It was discovered that the results of subjective and objective measurements of cyclovergence agreed exactly The largest fusional cyclovergence observed was 8 degrees The cyclovergence partly cancels out the cyclodisparity presented The greater part of the cyclodisparity usually remains The maximum aplitude of the sensory cyclofusion is of the order of 8 degrees The cyclovergence response is greatest when large fusion images with numerous horizontal contours are presented The motor mechanism of cyclofusion presupposes the existence of recently demonstrated cyclodisparity detectors The amplitude of sensory fusion is determined by the vertical diameter of the peripheral Panum areas

Crone Ra

Papers

Optically induced eye torsion. I. Fusion cyclovergence.