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Biomedical subjects

H Collewijn

Publications and source records attributed to H Collewijn.

At least 109 records · Page 6Linked to original sources
PubMed1978

Optokinetic eye movements in albino rabbits: inversion in anterior visual field.

When visual contrasts are restricted to the anterior sector (90 degrees to 180 degrees) of the albino rabbit's visual field, eye position is dramatically unstable, and when such contrasts are moved, horizontal optokinetic eye movements are inverted: the direction of pursuit is opposite to that of the stimulus. In the posterior visual field stability and optokinetic reactions are normal, as in all parts of the pigmented rabbit's visual field. This phenomenon may be one more of the complex of visual system defects linked to albinism.

Albinism↗
PubMed1977

Optokinetic and vestibulo-ocular reflexes in dark-reared rabbits.

Rabbits were raised in complete darkness for 7 months after birth. Eye movements were measured at the end of this period and in the next 3 months of normal light exposure with chronically implanted scleral coils. Horizontal optokinetic nystagmus (OKN) was tested inside a large drum which was rotated at velocities between 0.06 and 60 degrees/sec. Vestibuloocular reflexes (VOR) were elicited by sinusoidal horizontal oscillation on a torsion swing at frequencies between 0.11 and 2.13 Hz and amplitudes up to 10 degrees. At the end of the light-deprived period (with the eyes still covered) a VOR could be elicited consisting of a normal mixture of smooth and saccadic components and normal phase relations, but the amplitude of the smooth (compensatory) component was reduced to about 1/3 of normal control values. At the first exposure to light an OKN could be immediately elicited which was normal in most respects, except for a reduction of the ratio slow phase eye speed/drum speed to about 2/3 of the value in normal controls. The preference of each eye for anterior motion and the quasiconjugate character of nystagmus in monocular stimulation were unaffected. Also the improvement of the VOR by vision was normal. No abnormal habituation or fatigeability were observed. In the next 3 months of normal light exposure about half of the amplitude defects in both systems were restored, largely in the first week. The remaining defects were apparently permanent.

Animals↗
PubMed1977

Eye- and head movements in freely moving rabbits.

1. Eye- and head movements were recorded in unrestrained, spontaneously behaving rabbits with a new technique, based upon phase detection of signals induced in implanted coils by a rotating magnetic field. 2. Movements of the eye in space were exclusively saccadic. In the intersaccadic intervals the eyes were stabilized in space, even during vigorous head movements. Most of this stability was maintained in darkness, except for the occurrence of slow drift. 3. Many saccades were initiated while the head was stationary. They were accompanied by a similar, but slower head rotation with approximately the same amplitude. The displacement of the eye in space was a pure step without appreciable under- or over-shoot. The deviation of the eye in the head was mostly transient. 4. Other saccades were started while the head was moving and were possibly fast phases of a vestibulo-ocular reflex. The time course of the eye movement in space was identical for all saccades, whether the head was moving prior to the saccade or not. Eye movements without any head movement were not observed. 5. Saccades were mostly large (average 20-6 +/- 12-4 degrees S.D.) and never smaller than 1 degree. The relations of maximal velocity and duration to amplitude were similar to those reported for man. 6. Visual pursuit of moving objects, when elicited, was only saccadic and never smooth. 7. It is concluded that the co-ordination and dynamics of the rabbit's head- and eye movements are similar to those of primates. In the absence of foveal specilization, the eye movements are restricted to a rather global redirection of the visual field, possibly in particular of the binocular area.

Animals↗
PubMed1975

Changes in compensatory eye movements after unilateral labyrinthectomy in the rabbit.

Compensatory (slow phase) eye movements elicited by sinusoidal oscillation on a torsion swing were measured in rabbits, 6 months after destruction of the left labyrinth. A range of combinations of stimulus frequencies (0.048-1.8 Hz) and amplitudes (1-25 degrees) were used. Gain (amplitude of cumulative slow phase eye movement/amplitude of swing), phase (eye position vs. swing position - 180 degrees) and directional asymmetry were calculated from averaged records. With eyes covered, gain was much less than half of normal and phase lead was increased by at least 20 degrees. Spontaneous drift was minimal or absent; a slight asymmetry of reactions (preponderance of smooth movements to the intact side) was found. In the presence of vision, reactions were slightly improved, but only for low stimulus velocities. It is concluded that although the acute effects of unilateral labyrinthectomy in rabbits subside and a static equilibrium is achieved, dynamic performance of vestibular reactions remains much below normal.

Animals↗
PubMed1975

Direction-selective units in the rabbit's nucleus of the optic tract.

A class of direction-selective (DS) units, histologically localized within the nucleus of the optic tract (NOT) was isolated in the rabbit's pretectum. These units typically had a maintained discharge of 25-50 action potentials/sec and large receptive fields (up to 40 X 150 degrees) in the visual streak area of the contralateral eye. They were excited by a visual pattern moving in one direction and inhibited by motion in the opposite direction. The reactions were sustained. Excitatory and inhibitory acceptance angles were each 180 degrees. Most units were excited by anterior motion of the stimulus and reacted to a wide range of velocities (0.01-20 degrees/sec). Random checkerboard patterns (elements 0.8 degrees), grids of black and white stripes (1, 2 and 4 degrees wide) and single black and white edges were all effective, with a decreasing response magnitude in roughly this order. A stimulus area of 2 X 2 degrees was already effective; response increased with area and was maximal for 15 X 15 degrees and larger stimuli. Latency for visual stimulation was 60 +/- 10 (S.D.) msec, for electrical stimulation of the chiasm 2.2 +/- 0.3 (S.D.) msec. Synaptic latency and presynaptic conduction velocity were estimated at 0.7 msec and 13m/sec, respectively. A strong convergence of retinal DS fibers upon NOT units is postulated. Since most properties of NOT units are compatible with those of optokinetic nystagmus, and electrical stimulation of the NOT elicits vigorous nystagmus, these data suggest that these cells are the essential afferent link in the optokinetic reflex arc.

Animals↗
PubMed1975

Oculomotor areas in the rabbits midbrain and pretectum.

The role of some meso- and diencephalic structures in eye movements was investigated by ablation and stimulation experiments. Optokinetic nystagmus was abolished by small lesions in the lateral pretectum, but not by complete removal of the superior colliculi. Stimulation of the superior colliculus and other visual centers was effective in eliciting nystagmus (slow phase ipsilateral), but the most efficient trigger zones are found in the lateral pretectum and the midbrain tegmentum. Only from these areas could nystagmus still be elicited after degeneration of the primary optic fibers. The lateral pretectal trigger zone is probably identical with the nucleus of the optic tract. It is postulated that this nucleus is an essential station for horizontal optokinetic reactions. Saccades were obtained by stimulation of the mesencephalic central grey, but not for any visual centers such as the superior colliculus.

Animals↗
PubMed1975

Eye movements due to linear accelerations in the rabbit.

1. Compensatory vertical or torsional eye movements of rabbits caused by linear accelerations along the transverse or sagittal axis were measured. Sinusoidal accelerations (parallel swing) in a frequency range of 0-068--1-22 Hz and acceleration steps (linear track) of 0-02--0-11 g were applied. 2. On the parallel swing, properties of the maculo-ocular reflexes were similar for transverse and sagittal acceleration. Gain (rotation of eye/rotation of the resultant linear vector) proved to be very low: about 0-1 for 0-3 Hz and smaller than 0-01 for frequencies above 1-0 Hz. The decrease in gain was accompanied by an increase in phase lag to about 180degrees. No non-linearity was revealed by the use of different amplitudes (10--30 cm). 3. On the linear track, eye deviation after an acceleration step took many seconds to develop fully. Gain increased with time and was about 0-65 after 5 sec. 4. The results indicate that the responses of the otoliths, as reflected in maculo-ocular reactions, are very slow. Fluctuations in the direction of gravity seem to be averaged over several seconds by the system. This may explain that erratic linear accelerations(frequency greater than 1 Hz) during locomotion or transport do not lead to eye movements or disorientation.

Acceleration↗
PubMed1974

Vestibulo-ocular and optokinetic reactions to rotation and their interaction in the rabbit.

1. Compensatory eye movements due to sinusoidal yaw movements on a torsion swing were measured in alert rabbits. A range of combinations of frequencies (0.048-1.8 Hz) and amplitudes (1-25 degrees ) were used. Gain (cumulative slow phase eye movement amplitude/swing amplitude) and phase (eye position vs. swing position - 180 degrees ) were calculated from averaged records.2. Eyes were either closed (canal-ocular reactions only), open in earth-fixed visual surroundings (natural interaction of vestibular and optokinetic reactions), or looking at platform-fixed surroundings, which rotated with the animal (conflict situation). In some rabbits, the same stimulus programme was applied a month after bilateral destruction of the labyrinths (optokinetic reactions only).3. For canal-ocular reactions, no true threshold was found. Yet the system showed a small but systematic non-linearity which is tentatively explained by an acceleration-dependence of gain. For the higher frequencies (0.40-1.8 Hz) used, gain was 0.55-0.75, with a decrease at the lower frequencies, down to 0.16-0.33 at 0.048 Hz. The response showed a phase-lead of about 45 degrees at 0.048 Hz and was nearly in phase at 1-1.8 Hz. The long time constant of the cupula-endolymph system was estimated at about 3.3 sec.4. With earth-fixed visual surroundings a frequency-independent gain (range 0.55-0.82) with negligible phase error was found for the entire stimulus range tested. This natural combination of canal-ocular and optokinetic systems appears to function very efficiently, with mutual correction of the defects of the systems apart.5. With platform-fixed visual surroundings the canal-ocular system was severely inhibited and its non-linearities were markedly enhanced by the optokinetic system, especially when the torsion swing moved slowly.6. The general shape of input-output relations of optokinetic reactions after labyrinthectomy were similar to those found earlier in normal animals, but gain was subnormal for the entire stimulus range tested.

Animals↗