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At least 937 records · Page 52Linked to original sources
PubMed1984

Visual localization with eye movements: a review.

This paper reviews and discusses the most popular theories which have been proposed to account for the stability of the visual environment during eye movements. The subject is discussed chiefly from the stand-point of phylogeny rather than its contemporary treatment which attempts to explain neural mechanism by analogy with robotic systems or models. Certain conclusions are formed, and it is postulated that the constancy of egocentric directions following an eye movement is affected by the same mechanism that serves to retain the positional constancy of objects during the operation of the primitive postural reflex.

Afterimage↗
PubMed1983

Some aspects of amblyopia.

Some of the recently suggested methods for treating amblyopes are reviewed. A survey of the success rate in 50 young amblyopes, using conventional methods, is described. Whilst 26% did not improve at all in visual acuity, 50% improved by at least two Snellen lines. The suggestion is made that the success rate in the clinic described is similar to that found elsewhere.

Afterimage↗
PubMed1978

Different loci suggested to mediate tilt and spiral motion aftereffects.

Interocular transfer of two figural aftereffects was examined in orthotropes and strabismic subjects. Within both groups there were persons with an appreciable degree of stereoacuity and others who had little or none. Experimental evidence from a variety of sources has suggested that stereopsis depends upon binocularity of units in the geniculostriate system. For the tilt aftereffect, interocular transfer correlated with stereoacuity among both orthotropes and strabismics. For the spiral motion aftereffect, interocular transfer did not correlate with stereoacuity; it was present among orthotropes and absent among strabismic individuals. The correlation of stereoacuity with interocular transfer of the tilt aftereffect agrees with previous observations and is consistent with the interpreation that this effect is mediated at a cortical level. The lack of a correlation between stereoacuity and interocular transfer of the spiral motion aftereffect suggests that this effect is mediated by units other than those responsible for stereopsis. Richards and Smith, on the basis of certain phenomenal differences between the spiral motion aftereffect and other figural aftereffects, have suggested that the former is mediated at a midbrain level. If strabismic persons lack binocular units in midbrain, the present results are consistent with their hypothesis.

Afterimage↗
PubMedDate not supplied

Investigation of the horizontal, vertical, and oblique optokinetic nystagmus and afternystagmus in squirrel monkeys.

A moving random dot pattern was projected onto a tangent screen in front of awake untrained monkeys that were always placed in upright position. Eye movements were recorded in two dimensions to study the oblique optokinetic nystagmus (OKN) and compare it to the horizontal and vertical OKN. Any direction of pattern movement across the screen could be achieved. The angular velocity of pattern movement was varied between 6 and 180 degrees/s. To display off-horizontal and off-vertical eye movements, the instantaneous direction and velocity of the eye movements were computed from the horizontal and vertical search coil voltages. At pattern velocities below 90 degrees/s, stimulus-direction and direction of the OKN slow phase matched very precisely. Above 90 degrees/s the slow-phase eye movement direction was systematically shifted toward the horizontal except for pure vertical stimulation. The slow-phase eye velocity at off-horizontal stimulation was inconstant, however; stable periods occurred repeatedly that were used to define the gain of OKN. Up to stimulus speeds of about 90 degrees/s the OKN gain did not depend on the direction of stimulation and of OKN. At higher velocities the gain decreased with the increasing angle between stimulus direction and horizontal. Practically no vertical optokinetic afternystagmus (OKAN) could be observed, in either the up or down direction. At the onset of afternystagmus after oblique stimulation the direction of the OKAN slow phase immediately shifted over to the horizontal. The data indicate that the slow-phase direction and gain of oblique OKN with the monkey's head upright can be described by the sum of a horizontal and a vertical velocity vector obtained during stimulation in these cardinal directions.

Afterimage↗
PubMed1994

Computational principles in Purkinje I and IV reflection pattern evaluation for the assessment of ocular alignment.

PURPOSE: To develop a standardized reasoning for the evaluation of Purkinje I and IV Reflection Pattern data in primary, secondary, and tertiary positions of gaze in the diagnosis of strabismus with a mathematical approach. To demonstrate the applicability of certain mathematical relations and the appropriate graphic representation of computed ocular alignment data. METHODS: Starting from the known Reflection Pattern Evaluation formulae, equations were derived that allowed for the computation of the relative and absolute positions of the optical and visual axes of both eyes from original data in binocular and monocular fixation. These equations were simplified for clinical use. RESULTS: The authors obtained a set of equations that could be applied to the objective, quantitative analysis of eye alignment in screening for microtropia, in concomitant and incomitant diagnoses of strabismus in primary and nonprimary positions. CONCLUSIONS: Purkinje I and IV Reflection Pattern Evaluation can be extended to the diagnosis of strabismus in nonprimary positions with sufficient clinical accuracy. The newly presented principles and equations serve as a basis for a convenient graphic representation of Purkinje I and IV Reflection Pattern data. These principles of evaluation may be applied to any data dealing with ocular alignment, independently of the method.

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PubMed1994

Measurement of ocular alignment with photographic Purkinje I and IV reflection pattern evaluation.

PURPOSE: To provide reference data for the measurement of ocular alignment and of angles of strabismus with a new stationary photographic apparatus at near and at distance fixation; to verify quantitative relations between the data by comparing experimental data with theoretical predictions. METHODS: Use of Purkinje I and IV Reflection Pattern Evaluation in conjunction with a new stationary photographic apparatus; application of previously derived equations; simulation of angles of strabismus of 5 degrees and 10 degrees in the primary position. RESULTS: Data from 62 subjects with orthotropia show good linearity of measured angles in different directions of gaze; a 95% confidence interval for errors up to 18.6% in the simulated angles of strabismus; no need for individual calibration of the apparatus; no bias due to wearing of spherical corrections, and a detection threshold for microstrabismus of +/- 0.35 degrees. CONCLUSIONS: Data concerning orthotropic and simulated strabismus prove the accuracy of Reflection Pattern Evaluation to assess ocular alignment, for instance, for the diagnosis of strabismus in primary and secondary positions, at near and distance fixation. The measuring range can easily be extended to larger angles of strabismus.

Adult↗
PubMed1994

The interaction of otolith organ stimulation and smooth pursuit tracking.

The interaction of otolith organ stimulation and horizontal pursuit eye tracking in humans was studied in two different paradigms. In the first we measured the effects of lateral linear acceleration on ocular tracking of a retinal after-image, as compared to eye movements produced by acceleration alone (the linear VOR). The second paradigm determined the improvement in smooth oculomotor tracking presumably due to otolith input, by comparing tracking of an earth-fixed target during subject motion to tracking of target motion with the subject stationary. Subject and target motions in each case were sinusoidal. After-image tracking enhanced the gain of the linear VOR by a factor of 2 to 10. This is interpreted to mean that oculomotor efferent copy information is used to reconstruct an internal representation of target velocity, which is then tracked by the oculomotor system in the after-image condition. In the second paradigm, linear motion information transduced by the otolith organs combined with visual target information to yield improved oculomotor tracking over either system alone.

Adult↗
PubMed1994

Interocular transfer of the movement aftereffect in central and peripheral vision of people with strabismus.

PURPOSE: To compare binocularity in central and peripheral vision of people with early-onset strabismus and people with normal binocular vision. METHODS: Ten subjects with early-onset strabismus, and nine subjects with normal binocular vision were tested. To assess binocularity, interocular transfer (IOT) of a rotary movement aftereffect (MAE) was measured. The MAE stimuli were either confined to the central 2.8 degrees of the visual field or were presented 10 degrees into peripheral vision. RESULTS: In peripheral vision, there was no significant difference in IOT for the two groups of subjects. In central vision, there was a significant decrease of IOT in subjects with early-onset strabismus. Their IOT was, however, significantly greater than zero. CONCLUSIONS: Early-onset strabismus appears to spare binocularity in peripheral vision but reduces it in central vision. It does not abolish binocularity assessed by IOT of MAE, suggesting that some binocular connections survive early-onset strabismus, even in central vision.

Adolescent↗