Hans O Richter

University of Gävle · Department of Occupational and Public Health Sciences

Mobile technology has revolutionised how we work. It is now relatively easy to work anywhere and anytime, but this has placed the onus is on mobile (or flexible) workers to set up their own work environment for comfort and ease of use. Vision is an important driver of posture, and hence visual ergonomics principles are integral for setting up digit...

Introduction: The main purpose of this cross-sectional study was to investigate whether visual discomfort acts as a mediating factor between perceived visual ergonomic working conditions and self-rated visual performance among office workers who carry out administrative tasks and computer-based work at the Swedish Tax Agency. Methods: A questionnai...

The purpose of the present study was to extend the knowledge of functional linkages between visual and mental load, performance, and prefrontal cortex (PFC) activity, during forestry forwarding work. Eleven healthy participants, range 21–51 years old, with a minimum of 1-year work experience, carried out the task of loading logs along a standardize...

The present study aimed to identify whether or not an increase in ciliary-muscle contraction force, when the eye-lens is adjusted for viewing at a near distance, results in an increase in trapezius muscle activity, while performing a natural work task. Twelve participants, ranging in age from 21 to 32 years, performed a computer-mouse work task dur...

[This corrects the article DOI: 10.3389/fnhum.2018.00298.].

Purpose: To extend our knowledge of the functional linkages between visual fatigue and regional cerebral prefrontal cortex (PFC) oxygenation, we measured time related hemodynamic changes over the right dorsolateral prefrontal cortex (dlPFC) during convergence load under conflicting stimulus-to-accommodation and stimulus-to-vergence eye movements wi...

Visually demanding near work can cause eye discomfort, and eye and neck/shoulder discomfort during, e.g., computer work are associated. To investigate direct effects of experimental near work on eye and neck/shoulder discomfort, 33 individuals with chronic neck pain and 33 healthy control subjects performed a visual task four times using four diffe...

Purpose To evaluate the reliability and validity of the 15-item Visual, Musculoskeletal, and Balance Complaints Questionnaire (VMB) for people with visual impairments, using confirmatory factor analysis (CFA) and with Rasch analysis for use as an outcome measure. Methods Two studies evaluated the VMB. In Study 1, VMB data were collected from 1249...

Fatigue is a phenomenon of pronounced importance in sports. Recently, there is strong evidence of interplay between the prefrontal cortex and motor output during fatiguing contractions. The dorsolateral prefrontal cortex (DLPC) due to its large involvement in cognitive and motor activities is believed to be involved but this requires physiological...

Purpose. To investigate whether patients with age-related macular degeneration (AMD) run a potentially higher risk of developing visual, musculoskeletal, and balance complaints than age-matched controls with normal vision. Methods. Visual assessments, self-rated visual function, self-rated visual, musculoskeletal, and balance complaints, and percei...

Information technology (IT) has increased and changed the load for individuals in the workplace. Small displays and small text size on many IT applications lead to reduced viewing distances and poorer postures, with increasing biomechanical and oculomotor loads as results. Mental stress related to the high amount of information received and process...

We intended to assess consequences of reduced visual acuity for performance in a natural simple motor task (tracing) using objective kinematic performance measures. Specifically, we intended to elucidate the kind of relationship between the task performance and best corrected binocular visual acuity and to determine the threshold of visual acuity w...

Near work is associated with increased activity in the neck and shoulder muscles, but the underlying mechanism is still unknown. This study was designed to determine whether a dynamic change in focus, alternating between a nearby and a more distant visual target, produces a direct parallel change in trapezius muscle activity. Fourteen healthy contr...

To investigate if trapezius muscle activity increases over time during visually demanding near work. The vision task consisted of sustained focusing on a contrast-varying black and white Gabor grating. Sixty-six participants with a median age of 38 (range 19-47) fixated the grating from a distance of 65 cm (1.5 D) during four counterbalanced 7-min...

Objective: To determine whether the Feldenkrais method is an effective intervention for chronic neck/scapular pain in patients with visual impairment. Design: Randomized controlled trial with an untreated control group. Setting: Low vision center. Participants: Patients (NZ61) with visual impairment (mean, 53.3y) and nonspecific chronic (mean, 2...

A time honored dictum states that the eyes "lead the body", i.e. that the body typically adjust its position to compensate for an impoverished retinal image (e. g., as due to optical blur, and/or inappropriately sized visual target). But only moderate or low level of evidence exists in support of this view. Inconclusive evidence does not, however,...

Background: Symptoms from the eyes are common among computer users. Knowledge is scarce about these problems, however. Objectives: The aim was to study risk-factors, incidence and persistence of eye-symptoms among professionally active computer users. Methods: This was a questionnaire based prospective study where 1283 males and females from d...

Poor visual ergonomics is associated with visual and neck/shoulder discomfort, but the relation between visual demands and neck/shoulder muscle activity is unclear. The aims of this study were to investigate whether trapezius muscle activity was affected by: (i) eye-lens accommodation; (ii) incongruence between accommodation and convergence; and (i...

In this experimental study different levels of oculomotor load were induced via optical trial lenses. The aim was to investigate the temporal dependence of a moderate visual load on trapezius muscle activity. Trapezius muscle activity was measured with bipolar surface electromyography (EMG). Sixty-six subjects with a median age of 36 (range 19---47...

ABSTRACT The authors present a study of the relationship between individual variation in working memory capacity (WMC) and visually guided hand control in the face of visual distraction. WMC was assessed with the automated operation span task. Hand control was measured by requesting participants to track a visual target with a hand-held touch scree...

Frequent use of digital information technology has an impact on eye- and neck/shoulder-discomfort. Studies with cross sectional and intervention design indicate an association between the two symptom categories. Still, whether visually demanding near work, per se, contributes to increased neck/shoulder discomfort remains a question of debate. The a...

Visual strain and discomfort may contribute to the generation of work-related musculoskeletal disorders among e. g. computer workers. A positive correlation on a group level between eye-lens accommodation and trapezius muscle activity has been reported. In this study we investigated the possibility of a direct, fast, connection between lens accommo...

In an experimental study two levels of oculomotor load were induced via optical trial lenses. Trapezius muscle activity was measured with bipolar surface electromyography and normalized to a submaximal contraction. Sixty-six subjects with a median age of 36 (range 19-47, std 8) viewed a black and white Gabor grating (5 c/deg) for two 7-min periods...

Abstract Prolonged computer use, especially if fatigue ensues, is associated with visual and musculoskeletal symptoms. The aim was to determine the time-course of perceived fatigue in the wrist, forearm, shoulder and eyes during a 60-min mouse task (painting rectangles), and whether object size and/or mouse use demands were of influence. Also, we i...

The purpose of this experimental study was to investigate if sustained periods of oculomotor load impacts on neck/scapular area muscle activity. The static trapezius muscle activity was assessed from bipolar surface electromyography, normalized to a submaximal contraction. Twenty-eight subjects with a mean age of 29 (range 19-42, SD 8) viewed a hig...

To study the joint occurrence of eye-and-neck/scapular area symptoms and their association with occupational risk factors in a cross-sectional sample of professional information technology users. The participants consisted of 3,971 employees who worked with computers for a minimum of one hour a day. 2,551 (73%) were men and 945 (27%) women, with an...

In an experimental study four levels of oculomotor load were induced binocularly. Trapezius muscle activity was measured with bipolar surface electromyography and normalized to a submaximal contraction. Twenty-eight subjects with a mean age of 29 (range 19-42, std 8) viewed a high-contrast fixation target for four 5-min periods through: (i) -3.5 di...

The effect of neck/shoulder pain on the performance in a hand laterality motor imagery test was studied. Responses to the Cooper and Shepard (1975, Journal of Experimental Psychology: Human Perception and Performance 104 48-56) hand laterality test were explored in twenty-four individuals with chronic non-specific neck pain and twenty-one subjects...

Introduction: Age-related Macular Degeneration (ARMD) patients often describe complaints from neck and scapula area muscles and a decreased postural control. In clinical assessment, these complaints are considered to be due to old age. Purpose: This study focuses on low-vision patients with ARMD, comparing them to age-matched controls without any e...

The purpose of this work is to compare the relative contributions from the extraocular and sensory systems on the magnitude of the horizontal-vertical illusion (HVI). The visual HVI refers to the general tendency to overestimate vertical extensions of small-scale lines on a picture plane relative to the horizontal by 4-16% depending on the method o...

The purpose of this work was to characterize contrast sensitivity (CS) under short-wavelength illumination in 20 symptom-free subjects and eight asthenopics: all had normal unaided or corrected visual acuity and no sign of oculomotor disease. Threshold CS was assessed using the von Békésy tracking method from a viewing distance of 2.4 m (0.40 D). T...

OBJECTIVES: Few, if any, studies have investigated whether eyestrain and shoulder–neck symptoms are correlated, although functional links could be expected on the basis of neurophysiological evidence. This cross-sectional study assessed correlations between self-reported eyestrain and shoulder–neck symptoms among call center workers, while controll...

OBJECTIVES: This experimental pilot study assessed the effects of sustained low-level accommodative vergence loads on oculomotor performance, eyestrain, and musculoskeletal functioning. METHODS: A high-contrast fixation-point stimulus [light-emitting diode (LED)] was introduced into the optical axis of the viewing eye or into the midline in case of...

The purpose of this work is to identify human neural circuits involved in inhibition of accommodation/vergence by contrasting the cortical functions subservient to negative voluntary accommodation/vergence (NVA) with those evoked by active fixation in darkness (FIX). Five subjects with normal corrected acuity were studied using positron emission to...

The purpose of this study was to identify the networks involved in the regulation of visual accommodation/vergence by contrasting the cortical functions subservient to eye-lens accommodation with those evoked by foveal fixation. Neural activity was assessed in normal volunteers by changes in rCBF measured with PET. Thirteen right-handed subjects pa...

For 1 week, healthy human participants ( n=7) were devoid of normal vision by exposure to prism lenses that optically rotated their perceived world around the line of sight by 180 degrees. Adaptation to such prisms involved sustained and vigorous practice of the ability to redirect the unadapted efferent motor command; because prior to all visually...

The purpose of this work is to compare the relative contributions from the extraocular and sensory systems on the magnitude of the horizontal–vertical illusion (HVI). The visual HVI refers to the general tendency to overestimate vertical extensions of small-scale lines on a picture plane relative to the horizontal by 4–16% depending on the method o...

Nine young emmetropes were exposed to either 10 or 20 minutes of visual display terminal (VDT) work at 20 cm (5.0 D). In the first phase of the study, individual measures of the accommodative nearpoint, degree of phoria at near, and visual discomfort/asthenopia were obtained and contrasted to a baseline condition of no VDT work. The group average b...

This study identifies brain regions participating in the execution of eye movements for voluntary positive accommodation (VPA) during open-loop vergence conditions. Neuronal activity was estimated by measurement of changes in regional cerebral blood flow (rCBF) with positron emission tomography and 15O-water. Thirteen naive volunteers viewed a chec...

Psychophysical scales of a 3,3 c/deg monochromatic checkerboard of variable contrast were compared with steady state visually evoked potentials (VEP) recorded by gross electrodes on the scalp. These estimates of neuronal population responses grew as a power function of physical contrast having an exponent of approximately the same magnitude as the...

The neural circuits associated with the human monocular near/far response (NFR) were studied in thirteen normal volunteers by changes in relative regional cerebral blood flow (rCBF) measured with H215O infusion and positron emission tomography (PET). Behavioral tasks were selected to differentially recruit relevant circuits in three states of activ...

This conference was instigated by a combination of factors: The nature of the problem, the wide­ spread occupational epidemiology reported on eye symptoms and eye fatigue in the workplace, and the organizers' awareness of the complexity of the scientific and clinical bases of knowledge that might be usefully applied. The introduction of new methods...

Six human subjects were asked to draw ellipses presented on a screen by moving a manipulandum that controlled the position of a cursor. Six visual templates were used, which comprised three different ellipses displayed either horizontally or vertically; the ratio between the major and minor axes was 2, 4, or 5. For each visual template, the gains w...

In order to examine the relationship between reduced visual acuity in human strabismic amblyopia and the cortical activation pattern, we studied, by use of positron emission tomography (PET) and the H2(15)O bolus technique, changes in the regional cerebral blood flow (rCBF) induced by monocular visual stimulation of 8 individuals with this disorder...

Purpose. A PET aciivalion study was performed to examine if meaningful differences in the activalion pattern of regional cerebral blood flow (rCBF) could be obtained between the two eyes in amblyopic patients, using contrast-defined stimuli and quantitative procedures of image processing. Methods. The eight aduli patients displayed suppression of t...

The speed of laser speckles induced by refractive defocus was determined by means of the direct method of free magnitude estimation in combination with sensory verbal descriptors. Physical measures of angular velocities were obtained by matching a similar pattern under the viewer's control to the laser speckles for equal subjective velocity. Theore...

This study examined negative volitional accommodation under open-loop viewing conditions by means of a coherent laser light pattern (633 nm) whose direction and velocity of motion is determined by the refractive state of the eye. Using the direct scaling procedure of free magnitude estimation, the subjects were required to quantitatively judge velo...

In six subjects with normal corrected vision, perceived suprathreshold contrast of a sine‐wave grating pattern was assessed by an intermodal matching technique in combination with the method of ratio estimation. Vertical gratings were produced on an oscilloscope screen at spatial frequencies of 1.0, 2.0, 3.5, 5.0, 9.0 and 15.0 cycles per degree (c/...

Thesis (doctoral)--Uppsala University, 1993. Includes bibliographical references (p. 29-36).