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PubMed1995

Regulation of static and dynamic ocular alignment in patients with trochlear nerve pareses.

Ocular alignment and saccades were studied in seven patients with trochlear nerve pareses, before and after strabismus surgery. Prior to surgery, a position-dependent vertical ocular misalignment was present, and downward saccades were hypometric in the paretic eye. Strabismus surgery reduced the magnitude and position-dependence of the static misalignment. Saccade conjugacy improved in the patients with congenital pareses, and in the patient with a gradual-onset acquired paresis, but less improvement occurred in subjects with traumatic pareses. The post-operative change in saccade conjugacy relative to the change in static alignment correlated with pre-operative vertical vergence, suggesting that changes in saccade yoking depend on an interaction between saccades and vertical vergence.

Adaptation, Ocular↗
PubMed2001

Unilateral light-dark transitions affect choroidal blood flow in both eyes.

There is recent evidence that the perfusion of the choroid changes during dark-light transitions. We set out to investigate this response in more detail and to elucidate possible mechanisms involved in this process. For this purpose, the effect of dark-light transitions on choroidal perfusion was studied in healthy subjects. Choroidal blood flow and ocular fundus pulsation amplitude were measured as indices of choroidal perfusion during dark-light transitions using laser Doppler flowmetry and laser interferometry, respectively. In the first experiment, subjects were first kept in room light for 20 min, then light conditions were changed to darkness for 20 min, and thereafter, subjects were exposed to room light again. Both choroidal parameters decreased (-12% to -14%) during darkness but returned to baseline after the final room light period. In the second experiment, the index eye underwent the same procedure, whereas the contralateral eye was kept in light throughout the experiment. Choroidal haemodynamic parameters in the index eye reacted in a way comparable to that seen in the first experiment. The eye that was kept in light also reacted, but the effect tended to be less pronounced than that seen in the index eye (-8% to -10%). The observation that choroidal blood flow in both eyes reacts during unilateral light-dark transitions indicates that choroidal perfusion rate is adapted to retinal illumination conditions by neural control mechanisms.

Adaptation, Ocular↗
PubMed1994

Electrophysiology testing and the ophthalmic registered nurse.

Ophthalmologists employ electrophysiologic testing to diagnose and manage a variety of ocular conditions. The most common reason these tests are performed is to diagnose inherited vitreoretinal diseases. Patients of all ages may require electrophysiologic testing. The purpose of this article is to provide the ophthalmic registered nurse with a working knowledge of the three most commonly used electrophysiologic tests. We will provide background and practical information on how we perform electroretinography (ERG), electroculography (EOG), and dark adaptometry. Knowledge of the basics of this specialized testing will allow the ophthalmic nurse to provide more information for the patient. This knowledge will hopefully reduce patient anxiety and with better cooperation produce more accurate test results.

Adaptation, Ocular↗
PubMed1979

The effect of oxazepam on ocular readaptation time.

The readaptation time (RAT) is the interval during which a person exposed to a bright intense light flash cannot perceive a given target. In this study the target used was an optokinetic pattern and the elicited nystagmus (OKN) was registered with electrooculography (EOG), thus giving an objective registration of RAT. Oxazepam in therapeutic doses was given to five healthy subjects and the RAT and serum concentrations of the drug were registered simultaneously at different time intervals. An almost parallel increase of RAT and serum concentration of oxazepam was recorded. This suggests that RAT reflects the depressant effect on the CNS of this drug and it may be used as an objective method of following the clinical effect of a depressant drug as a function of time after intake.

Adaptation, Ocular↗
PubMed2002

Ocular wave-front aberration statistics in a normal young population.

Monochromatic ocular aberrations in 108 eyes of a normal young population (n=59) were studied. The wave-front aberration were obtained under natural conditions using a near-infrared Shack-Hartmann wave-front sensor. For this population and a 5 mm pupil, more than 99% of the root-mean square wave-front error is contained in the first four orders of a Zernike expansion and about 91% corresponds only to the second order. Comparison of wave-fronts aberrations from right and left eye in 35 subjects, showed a good correlation between most of the second- and third-order terms and a slight (but not clear) tendency for mirror symmetry between eyes.

Adaptation, Ocular↗
PubMed1985

Comparison of the adaptation time constants of the vestibulo-ocular reflex and of the sensation of rotation during sinusoidal stimulation.

The influence of adaptation on the phase characteristic of both the vestibular-ocular reflex and the sensation of rotation is investigated. The experimental data can be described by a second-order model with an adaptation term. The adaptation time constant Ta is found to be 135 s for the vestibulo-ocular reflex while it has a much lower value, 47 s, for the sensation of rotation. The difference is only found in the low-frequency region.

Adaptation, Physiological↗
PubMed1988

Monocular adaptation of the saccadic system and vestibulo-ocular reflex.

This study asks whether or not adaptation of saccades and the VOR is constrained to be conjugate by Hering's Law. Changes in saccades and the VOR produced by surgically weakening one of the horizontal recti by recession or tenotomy were examined in monkeys with the affected eye patched. After the restoration of vision a rapid monocular recalibration of both saccades and the VOR was observed in preparations with a small or moderate muscle weakening. Preparations with a severe weakening exhibited little monocular adaptation but when the normal eye was patched exhibited a strong conjugate adaptation. Thus the results indicate that saccades and the VOR have the capacity for monocular recalibration but that this capacity is more limited than that for conjugate changes.

Adaptation, Physiological↗
PubMedDate not supplied

Visual-vestibular interaction with telescopic spectacles.

Vestibularly and visually driven eye movements interact to compensate for head movements to maintain the necessary retinal image stability for clear vision. The wearing of highly magnifying telescopic spectacles requires that such compensatory visual-vestibular interaction operate in a quantitative regime much more demanding than that normally encountered. We employed electro-oculography to investigate the effect of wearing of 2x, 4x, and 6x binocular telescopic spectacles on visual-vestibular interactions during sinusoidal head rotation in 43 normal subjects. All telescopic spectacle powers produced a large, immediate increase in the gain (eye velocity/head velocity) of compensatory eye movements, called the visual-vestibulo-ocular reflex (VVOR). However, the amount of VVOR gain augmentation became limited as spectacle magnification and the amplitude of head velocity increased. Optokinetic responses during wearing of telescopic spectacles exhibited a similar nonlinearity with respect to stimulus amplitude and spectacle magnification. Computer simulation was used to demonstrate that the nonlinear response of the VVOR with telescopic spectacles is a result of nonlinearities in visually guided tracking movements. Immediate augmentation of VVOR gain by telescopic spectacles declined significantly with increasing age in the subject pool studied. Presentation of unmagnified visual field peripheral to the telescopic spectacles reduced the immediate VVOR gain-enhancing effect of central magnified vision. These results imply that the VVOR may not be adequate to maintain retinal image stability during head movements when strongly magnifying telescopic spectacles are worn.

Adaptation, Ocular↗
PubMed1977

Readaptation time after photo stress. Alcohol-induced acute and post-alcohol 'hangover' changes in ocular readaptation time.

The effect of alcohol intake on readaptation time (RAT) after photo stress is studied. Ten healthy subjects were given 0.72 g alcohol per kg body weight to be consumed within 20 min. The tests were made during a total period of 11-12 h. The findings demonstrate that moderate blood alcohol concentrations induce definite changes in RAT. An average RAT-prolongation of 60-70% was seen during the acute phase of intoxication. RAT-prolongation ended before the blood alcohol concentration had reached zero, but did not have the same downward slope. Following a period of reduction, a new prolongation of RAT was observed. The lack of congruence between the RAT-curve and the blood alcohol curve in the acute phase of intoxication and the post-alcohol increase are discussed. It is concluded that the alcohol-induced RAT-changes probably are CNS-effects and that the equipment used constitutes a sensitive method of estimating these effects.

Adaptation, Ocular↗
PubMedDate not supplied

Effects of asymmetric vergence on compensatory eye movements during active head rotation.

The kinematics of the horizontal VOR for near fixation demand that VOR gain should change dependent on the target distance and the orientation of the head with respect to the target, or, equivalently, the amount of ocular vergence and the asymmetry of this vergence. Across two experiments, the gain of the VOR was measured in the right eye of humans who rotated their heads to the right or left while viewing a target placed either 22, 32.5 or 200 cm from the center of head rotation, in conditions with and without visual feedback. When the eye was in-line with the target, the measured VOR gain was up to 43% greater than when the eye was in an eccentric position. However, in the eccentric position, higher VOR gains were achieved with visual feedback of the target than without feedback, indicative of a visual component in the compensatory eye movement. Also, by changing the posture of the left eye but keeping the right eye constant, the VOR gain in the right eye was changed substantially during a subsequent head rotation. Hence, the positions of both eyes in their orbits determine the gain of the VOR in each eye.

Adaptation, Ocular↗
PubMed1985

Plasticity in the vestibulo-ocular and optokinetic reflexes following modification of canal input.

The vestibulo-ocular reflex (VOR), the optokinetic reflex (OKR), and their interactions were studied before and after unilateral horizontal canal (HC) plug. Two independent changes occur in the VOR following HC plug: (a) a drop in VOR gain which recovers rapidly, provided that monkeys are permitted normal visual-vestibular interaction (VVI); and (b) a deterioration in response characteristics at low frequencies, consistent with a decrease in effective VOR time constant. The latter occurs regardless of VVI and VOR gain recovery and progresses over several days. The time constant may recover, but only after several months. OKR responses are in keeping with the notion that they represent a combination of fast and slow processes. Results after HC plug suggest that the gain of the slow OKR process rises along with that of the VOR. Response characteristics of synergistic and antagonistic VVI behave as linear combinations of VOR and OKR response characteristics both before and after HC plug. Changes in VVI arising after HC plug simply reflect modifications in VOR and OKR response characteristics.

Adaptation, Ocular↗
PubMed2002

Pupil location under mesopic, photopic, and pharmacologically dilated conditions.

PURPOSE: To determine whether there are systematic changes in pupil location with changes in the state of pupil size and with other ocular variables. METHODS: High-resolution images of the pupil of the eyes of 70 subjects were taken using an infrared-sensitive camera. Images were obtained under mesopic, photopic, and pharmacologically dilated conditions. From the images, the center and diameter of the corneal limbus and the pupil were computed. In addition, the location of the first Purkinje image was calculated. RESULTS: The pupil center shifted consistently temporally as the pupil dilated. The total motion was relatively small, with a mean distance of 0.133 mm motion between the mesopic and photopic conditions, with the pupil diameter changing from 6.3 to 4.1 mm. Ninety percent of the subjects had a motion of less than 0.3 mm. One patient showed a motion of almost 0.6 mm. The change in location of the pupil center was not significantly related to refractive error, age, or the change of pupil diameter. CONCLUSIONS: Changes in the location of the pupil center with changes in the dilation of the pupil are typically slight, but can be significant in a few subjects, especially in pharmacologically dilated pupils.

Adaptation, Ocular↗
PubMed1986

[The working adaptation in visual display terminal (VDT) workers].

The working adaptation in VDT workers was conducted by investigating from two different standpoints: one was to indicate an improvement of working conditions and environments around the VDT workers, evaluating the fundamental data of their visual physiological functions, and the other was to investigate the relation between their performances and production. The results were as followed: 1. Eye strain induced by VDT work was able to take an objective view as accommodative and convergent depression including the tear productive function, followed by making good working conditions. 2. The measurement of eye movement was able to analyze the response time and the response process for the informations indicating on the display, and the concept of recovery time for deteriorated accommodative function was useful to improve the display design. 3. It was suggested that the measurement of visual evoked potential was more simple method to evaluate the workers' attention. 4. The relation between performance and psychological stress and the time course analysis of performance were studied, so that it was given suggestions as to assign suitably the work management and the working design to each VDT worker.

Accommodation, Ocular↗
PubMed1985

Post-suppression vestibulo-ocular reflex in man: visual and non-visual mechanisms.

The vestibulo-ocular reflex (VOR) was intermittently suppressed by fixating a head-fixed target (light on: 9 s; darkness: 2 s) during whole-body (60-100 deg/s peak; 0.01-0.17 Hz) sinusoidal and triangular oscillation about the vertical axis for about 2 min. Eye movements associated with intervals of darkness at different phases of body oscillation were stimulus-locked averaged, thereby estimating the "post-suppression VOR". The gain ( (eye velocity)/(head velocity) ) of the post-suppression VOR was generally 26-50% of the normal gain in maintained darkness. During sinusoidal body oscillation, the phase lead of the post-suppression VOR equalled or, at low frequencies, appeared to exceed the normal lead in maintained darkness. When the light was permanently extinguished after 2 min of intermittent suppression, an initially reduced VOR rapidly (e.g., 0.4 s) appeared and required 6-30 s to build up to normal again. These observations indicated that visual suppression of the VOR dissipated in darkness with rapid and slow components. During 0.17 Hz, 60 deg/s sinusoidal oscillation, the rapid (perhaps visual) component was responsible for 1/3, and the slow (perhaps non-visual) component for 2/3, of all suppressive effects.

Adaptation, Ocular↗
PubMedDate not supplied

Effect of decreased retinal illumination on frequency doubling technology.

PURPOSE: To investigate the effect of changes in retinal illumination on Frequency Doubling Technology (FDT). METHODS: Five eyes, of 5 adults who were free from identifiable ocular pathology, were examined using the Snellen chart and the Pelli-Robson chart, conventional automated perimetry, and the full threshold N-30 program of FDT. Each test was performed with and without a 0.9, 1.5, or 2.4 log unit neutral-density (ND) filter placed before the eye. Furthermore, the influence of pupil diameter on FDT test results was compared after treatment with pilocarpine or cyclopentolate with the influence of ND filters. RESULTS: All tests showed a decrease in sensitivity with decreasing retinal illumination. Frequency Doubling Technology showed an especially pronounced and significant decrease in sensitivity. The maximum mean threshold difference in FDT results with ND filter was 31.2 dB while that with the Humphrey Field Analyzer and the Pelli-Robson chart were 13.3 dB and 0.66 log contrast, respectively. The mydriatic state of the pupil increased the sensitivity of FDT and the miotic state decreased it to about the same extent as the the 0.9 ND filter. CONCLUSION: The change in retinal illumination has more impact on FDT than on spatial contrast tests and conventional automated perimetry. It is important to take this into account in evaluating FDT results.

Adaptation, Ocular↗
PubMed1997

Anticipatory locomotor adjustments for accommodating versus avoiding level changes in humans.

The control of locomotion has been studied from various perspectives related to the tasks of pattern generation, equilibrium control or adaptation to the environment. The last of these locomotor components has received comparably less attention, specifically pertaining to anticipatory adjustments. Continuing the work which has been conducted on both humans and cats, the present paper explores the nature of the differences in anticipatory locomotor adjustments for obstacle avoidance versus the accommodation to level changes. Six subjects walked in six different environments including no obstructions, a simple obstacle, two different level changes (a platform and stairs), and a combination of an obstacle with each respective level change. Full dynamic analyses allowed comparison of muscle torques as well as muscle power generated and absorbed at the lower limb joints across conditions. It was found that the previously shown robust lower limb reorganization characterized by a knee flexor generation strategy was upheld in all conditions when the obstacle was present. Pure level changes involved an augmentation of the ongoing hip strategy inherent in normal level walking. In the compound environment of obstructed level changes, subjects chose to combine an augmentation of hip flexor power with a reorganization to active knee flexion. The results are discussed from the point of view of general principles of mechanical coordination and the exploitation of intersegmental dynamics for foot transport.

Accommodation, Ocular↗
PubMed1980

The effect of welding fumes on ocular readaptation time.

The effect of welding fumes on ocular readaptation time (RAT) has been investigated. Objective measurements of RAT were obtained from a determination of the recovery time for optokinetic nystagmus following a bright flash of light. Welding electrodes of different types and chemical compositions were used. Welding fumes and the breathed gases were analyzed for particles, and the blood concentration of certain trace elements was determined. The results show that fumes from basic electrodes, containing high amounts of calcium and fluorides, and sometimes copper, produced a marked increase in RAT. The fumes from rutile electrodes, containing only low amounts of these substances, produced no demonstrable prolongation or RAT. Nor was RAT affected by the copper content of the electrodes. Thus the results appear to indicate that fluorides in the fumes produced by the basic electrodes cause the prolongation of RAT. The substances causing this prolongation seem to be bound to fume particles greater than 0.3 micron. Discomfort--nausea and headache--correlated with increased RAT prolongation. But analyses of the ambient air and of trace elements in the blood did not reveal any changes that could be correlated with the effect on RAT. RAT changes measured in conjunction with the inhalation of fumes from basic electrode welding are comparable to those seen after the intake of a therapeutic dose of oxazepam.

Adaptation, Ocular↗
PubMedDate not supplied

Electroretinographic findings in subjects after administration of fenretinide.

We measured the electroretinogram to determine whether ocular toxicity exists in men taking oral feretinide, 100 mg daily, for prevention of adenocarcinoma of the prostate. Male subjects at an increased risk for prostate cancer were recruited as volunteers. Fenretinide treatment took place over 1 year with a regimen of 100 mg/day for 25 days with 3 day hiatus intervals. Baseline testing included the electroretinogram Ishihara plates, and the Farnsworth-Munsell D-15 test. Subsequent electroretinographic testing was conducted at 4, 8, 12 and 18 months. Thirteen of 14 subjects maintained normal age-matched electroretinographic responses 6 months after fenretinide treatment. Of these 13 subjects, six showed slight decreases, within 1 standard deviation of the normal mean. Two subjects showed a slight gradual decline of rod-mediated a-wave amplitudes, while b-wave amplitudes were steady. One subject, who had glaucoma, unilaterally fell below normal. After treatment ended, all of the 13 subjects had electroretinographic responses at their respective baseline levels. The subject whose responses fell and remained below 1 standard deviation showed an overall decline in responses and, on follow-up, was diagnosed as having branch retinal vein occlusion, which most likely is the main contributor to the decrease in electroretinographic responses. Our results indicate that men taking 100 mg of oral fenretinide per day for 1 year, with a 3 day hiatus each month, do not show toxicity -induced retinal dysfunction, as measured by the electroretinogram.

Adaptation, Ocular↗