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PubMed2006

Neuro-ophthalmologic manifestations of psychogenic disease.

From a neuro-ophthalmologic standpoint, five areas may be affected by psychogenic disease: (1) vision, including visual acuity and visual field; (2) ocular motility and alignment; (3) pupillary size and reactivity; (4) eyelid position and function; and (5) corneal and facial sensation. The physician faced with a patient complaining of decreased vision or some other disturbance related to the afferent or efferent visual systems for which there is no apparent biologic explanation has three responsibilities. First, the physician must ascertain that an organic disorder is not present. Second, the physician should induce the patient to see or do something that would not be possible if the condition were organic in nature. Finally, the physician should attempt to determine whether the patient has an underlying psychiatric disease or is experiencing psychosocial stress. In this article, manifestations of psychogenic disease as they pertain to vision are considered, and, where appropriate, the various methods used to diagnose and treat these phenomena are discussed.

Accommodation, Ocular↗
PubMed2002

Smooth pursuit eye movements in patients with ocular motor nerve palsies: a preliminary report.

The trajectories, velocity, and co-ordination of smooth pursuit eye movements were investigated in 30 patients with ocular motor nerve palsies (including palsies of cranial nerves III, IV and VI). The recordings of horizontal and vertical eye movements were obtained by video-oculography under monocular viewing conditions. During the recordings, horizontal, vertical, and oblique target movements of 10 degrees /s constant velocity were presented to the subjects in succession. In contrast to normal subjects, smooth pursuit eye movements in patients with ocular nerve palsies showed considerable differences in dependence on the fixating eye. The smooth pursuit gain of the paretic eye was reduced for eye movements in the pulling plane of the paretic muscle. When viewing with the paretic eye, the tracking of the target was achieved by a series of refixation saccades, which also occurred in the occluded normal eye. Consequently, the sound eye position overshot the target. The transition from a smooth to a saccadic pursuit pattern was accompanied by a spatial deviation of the eye movement trajectories from the path of the fixation target.

Electrooculography↗
PubMed1984

The roles of target and eye motion in the production of the visual shift in prism adaptation.

Two experiments, with a total of 48 Ss, were performed to evaluate the possible determinants of the visual shift (VS) in prism adaptation. In Experiment 1 the effects of target movement and pursuit eye movements on resultant visual adaptation were investigated. Maximal VS was produced when both of these conditions were present. Experiment 2 was conducted to determine whether hypnotic anesthesia in and around the eyes and eye muscles reduces feedback from eye-position sensations and, consequently, the magnitude of the VS. This manipulation proved to be successful and virtually eliminated the production of VS. The results of the two experiments helped to identify two factors that contribute to the production of the VS: the presence of visual target movement during prism exposure and the accompanying eye movement which produces a change in the felt position of the eyes during target tracking.

Adaptation, Ocular↗
PubMed1980

The Maddox classification of vergence eye movements.

The classification of convergence as described by Maddox in The Clinical Use of Prisms is discussed. Maddox believed that the vergence system could be analyzed in terms of additive components designated according to their sensory origin: tonic vergence, accommodative vergence, reflex, or disparity (fusion), vergence, and proximal, or psychic, vergence. This description is brought into perspective with current-day descriptions of components of the binocular vergence system.

Accommodation, Ocular↗
PubMed1983

Static aspects of accommodation in human amblyopia.

Static aspects of accommodation in human amblyopia were investigated. Abnormalities uncovered included decrease in accommodative controller gain, decrease in slope of the accommodative stimulus/response curve, decrease in accommodative amplitude, and increase in depth of focus. Orthoptic therapy improved accommodative function in the amblyopic eye. Similar defects, but of lesser magnitude, were frequently found in the nondominant eyes of subjects in related test groups. This included former amblyopes who had received successful orthoptic therapy in their youth, which suggested lack of complete and/or maintained recovery of accommodative function, and strabismics without amblyopia, which suggested that the effects of strabismic suppression contributed to the accommodative deficits found in some strabismic amblyopes. The accommodative abnormalities found in our amblyopes were attributed to the effects of early, prolonged, abnormal visual experience on the sensory visual system.

Accommodation, Ocular↗
PubMed1995

Red-green opponent channel mediation of control of human ocular accommodation.

1. It has been hypothesized, but not verified empirically, that the control of human ocular accommodation is mediated by either the red-green or yellow-blue colour channels. Our goal was to determine experimentally whether the red-green channel by itself could influence the accommodative response. 2. To find out, we isolated the red-green channel through chromatic bandpass filtering and measured accommodation under dynamic and static conditions. The effect of this filtering was to modulate the red-green channel without disturbing either the yellow-blue or luminance channels. 3. Accommodative gain (ratio of response to stimulus amplitude) declined monotonically with decreasing bandwidth under dynamic conditions. Because the outputs of both the luminance and yellow-blue colour channels did not vary with bandwidth, the only explanation is that the red-green opponent process was responsible for the effect. 4. Under static conditions, however, accommodation was independent of bandwidth. This may be attributable to the decreased sensitivity to chromatic contrast that occurs at low temporal frequencies.

Accommodation, Ocular↗
PubMed2006

The extended horopter: quantifying retinal correspondence across changes of 3D eye position.

The theoretical horopter is an interesting qualitative tool for conceptualizing binocular correspondence, but its quantitative applications have been limited because they have ignored ocular kinematics and vertical binocular sensory fusion. Here we extend the mathematical definition of the horopter to a full surface over visual space, and we use this extended horopter to quantify binocular alignment and visualize its dependence on eye position. We reproduce the deformation of the theoretical horopter into a spiral shape in tertiary gaze as first described by Helmholtz (1867). We also describe a new effect of ocular torsion, where the Vieth-Müller circle rotates out of the visual plane for symmetric vergence conditions in elevated or depressed gaze. We demonstrate how these deformations are reduced or abolished when the eyes follow the modification of Listing's law during convergence called L2, which enlarges the extended horopter and keeps its location and shape constant across gaze directions.

Convergence, Ocular↗
PubMed2006

Does depth perception require vertical-disparity detectors?

Stereo depth perception depends on the fact that objects project to different positions in the two eyes. Because our eyes are offset horizontally, these retinal disparities are mainly horizontal, and horizontal disparity suffices to give an impression of depth. However, depending on eye position, there may also be small vertical disparities. These are significant because, given both vertical and horizontal disparities, the brain can deduce eye position from purely retinal information and, hence, derive the position of objects in space. However, we show here that, to achieve this, the brain need measure only the magnitude of vertical disparity; for physically possible stimuli, the sign then follows from the stereo geometry. The magnitude of vertical disparity--and hence eye position--can be deduced from the response of purely horizontal-disparity sensors because vertical disparity moves corresponding features off the receptive fields, reducing the effective binocular correlation. As proof, we demonstrate an algorithm that can accurately reconstruct gaze and vergence angles from the population activity of pure horizontal-disparity sensors and show that it is subject to the induced effect. Given that disparities experienced during natural viewing are overwhelmingly horizontal and that eye position measures require only horizontal-disparity sensors, this work raises two questions: Does the brain in fact contain sensors tuned to nonzero vertical disparities, and if so, why?

Algorithms↗
PubMedDate not supplied

Asymmetric horizontal tropias, DVD, and manifest latent nystagmus: an explanation of dissociated horizontal deviation.

Four patients with dissociated horizontal deviation (DHD) are described and an explanation of their horizontal comitant deviations is offered. The patients had asymmetric comitant horizontal deviations dependent on the fixing eye. All of them had unequal visual acuity (VA) and asymmetric manifest latent nystagmus (MLN) documented with eye movement recordings. The subjects appear to use convergence to reduce their nystagmus when viewing with the eye having more severe nystagmus and hence poorer vision. When patients viewed with the eye having less nystagmus, little or no convergence was exhibited. We suggest that DHD may be the manifestation of an asymmetric nystagmus blockage syndrome (NBS). The dampening effect of convergence on nystagmus has been well documented in the past and seems to apply here. The patients demonstrate that a true, but asymmetric NBS, can be found with MLN.

Child↗
PubMed2001

Stereopsis outweighs gravity in the control of the eyes.

The eyes are controlled by multiple brain circuits, some phylogenetically old and some new, whose aims may conflict. Old otolith reflexes counterroll the eyes when the head tilts relative to gravity. Newer vergence mechanisms coordinate the eyes to aid stereoptic vision. We show that counterroll hinders stereopsis, weakly when you look into the distance but strongly when you look near. The resolution of this conflict is that counterroll virtually vanishes when monkeys look close, i.e., stereopsis overrides gravity-driven reflexes but only on near gaze. This balance between gyroscopic and stereoptic mechanisms explains many other puzzling features of primate gaze control, such as the weakness of our otolith-ocular reflexes even during far viewing and the strange geometry of the primate counterpitch reflex, which rolls the eyes clockwise when monkeys look leftward while their heads are tipped nose up, but rolls them counterclockwise when the monkeys look rightward, and reverses this pattern when the head is tipped nose down.

Animals↗
PubMed2001

Differential sensorimotor processing of vestibulo-ocular signals during rotation and translation.

Rotational and translational vestibulo-ocular reflexes (RVOR and TrVOR) function to maintain stable binocular fixation during head movements. Despite similar functional roles, differences in behavioral, neuroanatomical, and sensory afferent properties suggest that the sensorimotor processing may be partially distinct for the RVOR and TrVOR. To investigate the currently poorly understood neural correlates for the TrVOR, the activities of eye movement-sensitive neurons in the rostral vestibular nuclei were examined during pure translation and rotation under both stable gaze and suppression conditions. Two main conclusions were made. First, the 0.5 Hz firing rates of cells that carry both sensory head movement and motor-like signals during rotation were more strongly related to the oculomotor output than to the vestibular sensory signal during translation. Second, neurons the firing rates of which increased for ipsilaterally versus contralaterally directed eye movements (eye-ipsi and eye-contra cells, respectively) exhibited distinct dynamic properties during TrVOR suppression. Eye-ipsi neurons demonstrated relatively flat dynamics that was similar to that of the majority of vestibular-only neurons. In contrast, eye-contra cells were characterized by low-pass filter dynamics relative to linear acceleration and lower sensitivities than eye-ipsi cells. In fact, the main secondary eye-contra neuron in the disynaptic RVOR pathways (position-vestibular-pause cell) that exhibits a robust modulation during RVOR suppression did not modulate during TrVOR suppression. To explain these results, a simple model is proposed that is consistent with the known neuroanatomy and postulates differential projections of sensory canal and otolith signals onto eye-contra and eye-ipsi cells, respectively, within a shared premotor circuitry that generates the VORs.

Action Potentials↗
PubMed2004

[The accommodative characteristics of gazing at stereoscopic images on a 3-D display].

PURPOSE: We measured the accommodative response in order to investigate the influence of a visual function when gazing at stereoscopic images presented on a three dimensional display. METHODS: Accommodative step responses were measured using an infrared optometer, setting the far target at the distance of 1 m and the near target at the distance of 50 cm. The step response of the right eye was examined 6 times at 10-second intervals. The far target was a starburst as a real image and the near target was a white circle on a random dot background on a parallax barrier system three-dimensional display as a stereoscopic image generated with a 90-min arc binocular crossed disparity(+1.5 degrees) and a 90-min arc binocular uncrossed disparity (-1.5 degrees), and a 0-min disparity (0 degree). The near target was presented in 4 ways: 1. -1.5 degrees disparity alone, 2. 0-min disparity alone, 3. +1.5 degrees disparity alone, and 4. +1.5 degrees and -1.5 degrees disparity alternately. RESULTS: In conditions 1 to 3, the mean +/- standard deviation values of the accommodative response were 0.59 +/- 0.16 D, 0.72 +/- 0.11 D, and 1.03 +/- 0.21 D, respectively. The accommodative response was very large at the disparity of +1.5 degrees compared with the disparity of 0 degree (p = 0.0300). It was not significant although there was a tendency to become small at the disparity of -1.5 degrees (p = 0.0707). In condition 4, the mean +/- standard deviation values of the accommodative response were 0.62 +/- 0.12 D in the condition of -1.5 degrees and 1.03 +/- 0.26 D in condition +1.5 degrees with significant difference (p = 0.0122). CONCLUSIONS: The over accommodation response is induced when gazing at a stereoscopic image under the condition of binocular crossed disparity. This indicates that gazing at stereoscopic images has ill effects on the accommodative system.

Accommodation, Ocular↗
PubMed1987

Near vision stress: vergence adaptation and accommodative fatigue.

Changes in the visual system following prolonged near work were investigated. Fifteen young, normal subjects undertook a severe, two hour long, binocular near visual task at 20 cm without any breaks. Fusional stress was assessed by near 'phoria change. Refractive change was measured with an autorefractometer to investigate whether transient myopia occurred and its subsequent recovery. The near task caused vergence adaptation which was primarily due to the fusional stress of the task (accounting for 67% of its variance). The 'phoria change was to a lesser extent (40%) dependent on the accommodative "stress" of the task. Fatigue of the accommodative system resulted in increased accommodative innervation to maintain the same accurate response. Increased innervation can continue after the task on subsequent distance viewing, resulting in transient myopia (mean 0.29 DS). This transient myopia was found to be due to a transient regression of the far point towards the subject's tonic accommodation level. This can be accounted for by a shift of the tonic level as well as an increased bias towards the pre-task tonic level.

Accommodation, Ocular↗