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Visual comfort in VDT operation: physiological resting states of the eye.

To recommend a comfortable visual display terminal (VDT) workstation design in an aspect of visual ergonomics, physiological resting states of the eye in 3 visual systems, pupil, vergence, and accommodation, were objectively investigated in 3 experiments. Experiment 1 ascertained a positive display polarity (dark characters on a bright background) and an illumination level of 500 lx to be the most appropriate working conditions, by using pupil analysis and subjective visual comfort in 10 subjects. Dark vergence, in experiment 2, was evaluated to be at a distance of about 50 cm from the eye, as an average in 14 subjects. Dark vergence was found to shift farther with an upward gaze while a nearer shift occurred with a downward gaze. In experiment 3, the average dark focus for 11 subjects was found to be 1.4 diopters (D) or a distance of about 74 cm from the eye. The positive correlation between refractive status of the eye and dark focus was statistically significant (r = 0.602). The ergonomic recommendations for a VDT workstation obtained in this study are a positive display polarity with an appropriate lighting condition, a downward gaze, and a viewing distance between 50 and 70 cm. These recommendations are considered to reduce visual fatigue due to prolonged VDT work and to facilitate visual comfort at work.

Accommodation, Ocular↗

Association between occupational asthenopia and psycho-physiological indicators of visual strain in workers using video display terminals.

BACKGROUND: There is a body of scientific literature examining functional changes in vision due to video display terminals (VDTs). The aim of our study was to determine the relationship of functional visual strain and symptoms of asthenopia and to evaluate the association between subjective and objective indicators of visual strain. MATERIAL/METHODS: Four hundred four office workers with and without involvement in VDT work were included in the study. To evaluate visual strain we used a questionnaire for subjective complaints, evaluated the main ophthalmologic indicators, and measured psycho-physiological indicators. RESULTS: The questionnaire data showed that 88.5% of the VDT workers complained of various vision disorders. VDT workers who complained of worsened vision, redness of the eyes, eye pain, and diplopia during work were found to show more significant changes in the psycho-physiological indicators objectively reflecting strain of the vision analyzer. In the group of people with symptoms of asthenopia, the differences in the indicators of visual sensomotoric reaction, constancy of clear vision, and changes in the periods of clear and unclear vision were statistically reliably greater than in people without symptoms of visual strain. CONCLUSIONS: The subjective perception of visual strain related to VDT work was confirmed by ophthalmologic and psycho-physiological measurements. Changes in ocular and psycho-physiological function before and at the end of the workday are a good objective index of visual and central nervous system strain.

Asthenopia↗

A very low level of magnetic field exposure does not affect a participant's mental fatigue and stress as much as VDT work.

Exposure to Magnetic Fields (MF) may affect the health of workers in an occupational environment. However, there is no clear evidence that the emission of MF from the visual display terminals (VDT) affects workers'mental status or induces stress in office environments. The purpose of our study was to investigate whether exposure to the MF during VDT work affects mental fatigue or induces stress related to psycho-physiological changes in workers. Thirty-seven students were voluntarily recruited to participate in this study. We created experimental conditions that a pair of the liquid crystal display (LCD) terminals separated by screens was closely placed in front of the visual suface of the cathode ray tube (CRT) units. All participants were not able to recognize whether the power of the CRT Units was ON or OFF while they worked with the LCD terminals. When the CRT unit was ON, participants who worked with the LCD terminal were called CRT-ON group. On the other hand, when the CRT unit was OFF, participants who worked with the CLD terminal were called CRT-OFF group. Incredibly short profiles of mood states (ISP)and subjective symptom questionnaires were used as indices of the mental fatigue as well as psychological stress before and after VDT work. Furthermore, salivary chromogranin A and urinary 8-hydroxydeoxyguanosine (8-OH-dG) were collected to measure physiological changes before and after VDT work. The results of the questionnaires and salivary and urinary stress markers showed that the exposure to the MF during VDT work did not significantly induce mental fatigue or psychological stress in comparison with the CRT-OFF group. Contrary to the results from the exposure, mood states of vigor decreased greatly (P < 0.05) whereas the states of fatigue and confusion increased significantly (P < 0.001) after VDT work. In the questionnaires for subjective symptoms, participants complained remarkably regarding 14 out of 25 conditions after VDT work. Moreover, urinary 8-OH-dG excretion increased significantly after VDT work. Taken together, the results of this study did not detect any bad health effects of MF exposure on the VDT participants but suggested that VDT work itself affects their mental fatigue and psycho-physiological status.

8-Hydroxy-2'-Deoxyguanosine↗

A laboratory-based investigation of relations among video lottery terminal (VLT) play, negative mood, and alcohol consumption in regular VLT players.

Thirty regular video lottery terminal (VLT) players were randomly assigned to 90 min of VLT play or a control activity (viewing a movie) to examine the impact of VLT play on alcohol use. Ratings of dysphoric mood were taken at baseline, midactivity, and postactivity. Alcoholic and nonalcoholic control beverages were available throughout. As hypothesized, those in the VLT condition were more likely to consume alcoholic than nonalcoholic control beverages (i.e., 73% drank alcohol and 20% drank control beverages), whereas no such preference for alcohol was observed in the movie control condition (i.e., 40% drank alcohol and 47% drank control beverages). Consistentwith predictions derived from Steele and Josephs' [J. Abnorm. Psychol. 97 (1988) 196; Am. Psychol. 45 (1990) 921.] attention allocation model, VLT condition participants who drank alcohol showed increases in dysphoric effect over the course of testing. No such changes in negative mood were observed in VLT participants who did not consume alcohol or in movie control participants regardless of whether they drank alcohol. An observed temporal pattern of greater drinking during the early phase of VLT play indicated that the relation between alcohol use and dysphoric affect among VLT condition participants could not readily be explained by drinking to relieve dysphoria induced by VLT losses. Clinical and policy implications are discussed.

Adult↗

Human-mouse gene identification by comparative evidence integration and evolutionary analysis.

The identification of genes in the human genome remains a challenge, as the actual predictions appear to disagree tremendously and vary dramatically on the basis of the specific gene-finding methodology used. Because the pattern of conservation in coding regions is expected to be different from intronic or intergenic regions, a comparative computational analysis can lead, in principle, to an improved computational identification of genes in the human genome by using a reference, such as mouse genome. However, this comparative methodology critically depends on three important factors: (1) the selection of the most appropriate reference genome. In particular, it is not clear whether the mouse is at the correct evolutionary distance from the human to provide sufficiently distinctive conservation levels in different genomic regions, (2) the selection of comparative features that provide the most benefit to gene recognition, and (3) the selection of evidence integration architecture that effectively interprets the comparative features. We address the first question by a novel evolutionary analysis that allows us to explicitly correlate the performance of the gene recognition system with the evolutionary distance (time) between the two genomes. Our simulation results indicate that there is a wide range of reference genomes at different evolutionary time points that appear to deliver reasonable comparative prediction of human genes. In particular, the evolutionary time between human and mouse generally falls in the region of good performance; however, better accuracy might be achieved with a reference genome further than mouse. To address the second question, we propose several natural comparative measures of conservation for identifying exons and exon boundaries. Finally, we experiment with Bayesian networks for the integration of comparative and compositional evidence.

Animals↗

[Could VDT use induce thoracic hyperkyphosis? Preliminary data].

The association between sitting posture and degenerative alterations of intervertebral disks has been widely studied, while the possible relationship between sitting posture and thoracic hyperkyphosis has not been investigated sufficiently. The objective of this study, therefore, is to verify the possible association between video display terminal (VDT) use, which needs a sitting prolonged posture, and thoracic hyperkyphosis. 63 VDT workers and 71 telephone line maintenance workers (control group) have been examined. The two groups were different for the postural load required by the two jobs. A questionnaire about job and clinical history has been administered to workers included in the study. A complete orthopedical examination has been performed for all workers, while radiographic exams have been performed only in the cases requiring of further diagnostic investigations. The two groups have resulted homogenous for age, while were different for working age and body mass index (BMI). The frequency of subjects with rachialgia has resulted higher in VDT users than in maintenance workers. The prevalence of thoracic hyperkyphosis observed in VDT users has been higher than in maintenance workers, with a difference near to be statistically significant, and significantly associated with age in VDT users. The hyperkyphosis of the dorsolumbar tract have resulted significantly more frequent in VDT users than in maintenance workers (p<0.05). Preliminary results of this study suggest that fixed and prolonged sitting working posture would be able to determine thoracic hyperkyphosis, although constitutional factors and age could have a role in its determination. Preventive measures should be proposed for an adequate ergonomic training of VDT users.

Adult↗

Skin changes in "screen dermatitis" versus classical UV- and ionizing irradiation-related damage--similarities and differences.

An increasing number of persons say that they get cutaneous problems as well as symptoms from certain internal organs, such as the central nervous system (CNS) and the heart, when being close to electric equipment. A major group of these patients are the users of video display terminals (VDTs), who claim to have subjective and objective skin- and mucosa-related symptoms, such as pain, itch, heat sensation, erythema, papules, and pustules. The CNS symptoms are, e.g. dizziness, tiredness, and headache. Erythema, itch, heat sensation, edema and pain are also common symptoms of sunburn (UV dermatitis). Alterations have been observed in cell populations of the skin of patients suffering from so-called "screen dermatitis" similar to those observed in the skin damaged due to ultraviolet (UV) light or ionizing radiation. In "screen dermatitis" patients a much higher number of mast cells have been observed. It is known that UVB irradiation induces mast cell degranulation and release of TNF-alpha. The high number of mast cells present in the "screen dermatitis" patients and the possible release of specific substances, such as histamine, may explain their clinical symptoms of itch, pain, edema and erythema. The most remarkable change among cutaneous cells, after exposure with the above-mentioned irradiation sources, is the disappearance of the Langerhans' cells. This change has also been observed in "screen dermatitis" patients, again pointing to a common cellular and molecular basis. The results of this literature study demonstrate that highly similar changes exist in the skin of "screen dermatitis" patients, as regards the clinical manifestations as well as alterations in the cell populations, and in skin damaged by UV light or ionizing radiation.

Computer Terminals↗

Psychosocial aspects of working with video display terminals (VDTs) and employee physical and mental health.

Psychosocial aspects of using video display terminals (VDTs) have been recognized as contributors to employees' mental and physical health problems for more than 15 years. Yet, little has been done by employers to change work organization conditions to improve the psychosocial work environment of VDT users. Thus, psychosocial aspects of work are emerging as one of the biggest problems for VDT users in the late 1990s. This paper explores how psychosocial aspects of VDT work are related to job stress, and their consequences for mental and physical health. Using the research literature, it defines various aspects of work organization and job design that have been shown to be related to VDT users' ill-health. Some of the important work design aspects uncovered include a lack of employee skill use, monotonous tasks, high job demands and work pressure, a lack of control over the job, poor supervisory relations, fear of job loss, and unreliable technology. These are the same job stressors that have been defined as problematic for a variety of blue collar jobs in previous research. Work organization improvements for healthier VDT jobs are proposed. These include organizational support, employee participation, improved task content, increased job control, reasonable production standards, career development, enhanced peer socialization, and improved workstation ergonomics. These organizational improvements are derived from a more detailed organizational strategy for job stress reduction. A model of job redesign through proper 'balancing' of work organization features is discussed.

Computer Terminals↗

[Changes in visual function caused by work at a data display terminal].

Working at video display terminals (VDTs) is particularly demanding in terms of orthopaedic and visual functions. This study was initiated to examine whether, and if so how, VDT work can influence the visual system. It was designed as a 5-year-prospective study based on the matched-pairs technique. The subjects were examined at the beginning and after 5 years of VDT work. The study group consisted of 102 people working at VDTs, and these were paired with 102 other office workers who did not use VDTs. The legally prescribed screening examinations of visual acuity (distance and near vision, phorias, stereopsis, and colour vision) were carried out. We also checked the anterior segments by examination with the slit-lamp and the fundus by ophthalmoscopy. Break-up time, Schirmer-I test, perimetry and tonometry were included in our range of examinations. We found a significant difference in asthenopia and daily hours of VDT work between VDT workers working less than 6 h daily and those working more than 6 h daily. In the study group pre-existing exophoria seemed to increase, but no statistical significance was found on testing. Nor was there any significant difference between the study group and the control group in the parameters examined in the course of the screening examination. In our investigation of monocular VDT workers (n = 3) we could not find any visual problems.

Adult↗

Validity of surrogates for determination of 30-1000 Hz magnetic field exposure for video display terminal users in office settings.

In studies investigating adverse reproductive outcomes associated with video display terminal (VDT) usage, amounts of time spent in front of a VDT or magnetic field (MF) levels in front of the VDT are used as surrogate measures of subject's MF exposure. However, the relevance of such surrogates to actual exposures has not been demonstrated, and the validity of the use of such measures as a surrogate for the actual MF exposure is only speculative. This study examines 1) measurements of MFs at frequencies of approximately 30-1000 Hz at a fixed distance from the VDTs, 2) reported hours of VDT use, and 3) reported distance between the VDT and the subject's waist as surrogate measures for the average MF exposure level of a VDT user during one 8 h workday. The results showed a weak correlation between the average exposure level of a VDT user and the MF 46 cm from a VDT (R = 0.52, n = 67, P < 0.001). This study showed no association between self-reported hours of VDT usage, or self-reported distance between waist and VDT, and the average MF exposures. Moreover, individuals' average MF exposures did not seem to be affected by other variables, such as position of a VDT on the desk, hours of desk use, and the VDT type (color vs. monochrome). These findings indicate that VDT exposures within office settings are complex and cannot be easily predicted by surrogates.

Computer Terminals↗

VDT-related musculoskeletal symptoms: interactions between work posture and psychosocial work factors.

Video display terminal (VDT) operators (n = 150) in the editorial department of a large metropolitan newspaper participated in a study of day-to-day musculoskeletal symptoms. Work posture related to the VDT workstation and psychosocial work factors were also investigated for their contributions to the severity of upper body pain, numbness, and stiffness using a representative subsample (n = 70). Self-report measures included Karasek's Job Content Instrument and the author-designed Work Interpersonal Relationships Inventory. Independent observations of work posture were performed using techniques similar to those reported by Sauter et al. [1991]. Pain during the last week was reported by 59% (n = 88) of the respondents, and 28% (n = 42) were categorized by symptom criteria potentially to have musculoskeletal disorders. More hours per day of VDT use and less decision latitude on the job were significant risk factors for potential musculoskeletal CTDs. Head rotation and relative keyboard height were significantly related to more severe pain and stiffness in the shoulders, neck, and upper back. Lower levels of co-worker support were associated with more severe hand and arm numbness. For both the region of the shoulders, neck, and upper back and the hand and arm region, however, the contributions of relative keyboard and seat back heights to symptom severity were modified by psychological workload, decision latitude, and employee relationship with the supervisor. Alternative explanations for these findings are discussed.

Adult↗

Structural stability and reliability of the Swedish occupational fatigue inventory among Chinese VDT workers.

The aim of the present study was to test the structural stability and reliability of the Swedish occupational fatigue inventory (SOFI) for use in a group of Chinese visual display terminal (VDT) workers. A qualified translator was recruited to translate the Chinese version of the SOFI (SOFI-C). The content validity was established with 12 bilingual practitioners and seven professional experts. The translated SOFI was administered to 104 sedentary workers on two occasions with an interval of 60 min. Most of them were female (80.8%) and they had a mean age of 34.5 years. Fifty-one percent of them reported using a VDT for 4h or more at work. Exploratory factor analysis revealed a five-factor solution, which was comparable to the original latent factors. Cronbach's alpha for the five-factor scales was between 0.88 and 0.95. The test-retest reliability was satisfactory with intra-class correlations ranging from 0.69 to 0.83. The workers who used a VDT for 4h or more had significantly higher SOFI scores than those who used one for less than 4 h (p = 0.007 - 0.046). The results indicated that the SOFI-C was valid and reliable for measuring fatigue among Chinese sedentary workers. The satisfactory structural stability suggested that cultural influences on the construct of fatigue were not strong. Its characteristics of discrimination of the sedentary workers who had high VDT exposure suggested that the SOFI-C would be a useful instrument for prevention and intervention programs designed for work-related injuries in the workplace.

Adult↗

VDTs: field levels, epidemiology, and laboratory studies.

As the use of video display terminals (VDTs) has expanded, questions have been raised as to whether working at a VDT affects the risk of adverse pregnancy outcome. A particular focus for these questions has been the very low frequency (VLF) magnetic field produced by a VDT's horizontal deflection coil. VDTs also produce VLF electric fields, extremely low frequency (ELF) electric and magnetic fields, and static electric fields, Ten studies of pregnancy outcome in VDT operators have been conducted in six countries, and with one exception, none has concluded that magnetic fields from VDTs may predispose pregnant operators to spontaneous abortion or congenital malformation. The epidemiologic studies conducted thus far do not provide a basis for concluding that VDT work and adverse pregnancy outcome are associated. Studies of fetal resorptions and malformations in rodents exposed to VLF magnetic fields have produced inconsistent findings. Two laboratories in Sweden that studied mice have reported positive results, one laboratory showing field-related malformations (but not resorptions) and the other showing field-related resorptions (but not malformations). Two Canadian laboratories have reported negative results in rats and mice. Studies of avian embryos have also yielded inconsistent results, but lacking a maternal-fetal placental interface, avian embryos are a questionable model for evaluating human reproductive risks. Finally, VLF electric and magnetic fields measured at the operator position are in compliance with field strength standards and guidelines that have been established around the world.

Animals↗

Video lottery terminal access and gambling among high school students in Montréal.

BACKGROUND: Gambling is a risky behaviour that involves uncertain financial outcomes, can be addictive, and has been associated with strongly adverse social and public health outcomes. We wanted to assess whether socio-economic and gambling-related-opportunity environments of neighbourhoods affected the uptake of video lottery terminal (VLT) gambling among Montréal youth. METHODS: Spatial and statistical analyses were conducted to examine geographical patterns of neighbourhood socio-economic conditions, VLT sites (n=407), and high school locations (n=305) within the Montréal Census Metropolitan Area (CMA). VLT concentration within high school neighbourhoods was measured to examine how the number of VLT opportunities varies according to socio-economic status of the school neighbourhood. A student survey was analyzed using logistic regression analysis to explore the role of individual (student) characteristics and environmental (neighbourhood) characteristics in predicting the VLT gambling behaviours reported among a sample (n=1206) of high school students. RESULTS: Video lottery gambling opportunities are more prevalent near schools located in socio-economically deprived neighbourhoods compared with schools located in more affluent neighbourhoods. The principal individual risk factors for VLT gambling were shown to be male sex, peer VLT-use, substance use, as well as the after-school routines of youth. INTERPRETATION: The spatial distribution of VLTs reflects local geographies of socio-economic disadvantage and may have a pronounced impact on students attending schools in lower income neighbourhoods, especially those with individual risk factors. Efforts to reduce gambling-related public health costs may want to take into account the socio-spatial distribution of gambling opportunities, particularly in the local environments that youth frequent.

Adolescent↗

Carpal tunnel syndrome in male visual display terminal (VDT) workers.

BACKGROUND: The association between working at a video display terminal (VDT) and development of carpal tunnel syndrome (CTS) is not well-established. The study surveyed the prevalence of CTS symptoms, explored the risk factors and evaluated the clinical application of hand diagrams, physical tests and electrodiagnosis among male VDT workers. METHODS: A cross-sectional study was performed in an information and communication technology company. Three-forty questionnaires were completed and 82 volunteers participated in the physical examination and nerve conduction study. The personal and occupational risk factors for CTS were analyzed. RESULTS: The prevalence of CTS symptoms was 3.8% among 340 subjects, while prolonged median motor distal latency (>4.2 msec) was disclosed in 3.7% of a subgroup receiving examination. Classic/probable CTS symptoms was associated with high body mass index (>28 kg/m(2), odds ratio = 4.1, P = 0.029) and moderate job seniority (3-5 years, odds ratio = 4.6, P = 0.023). Prolonged median motor distal latency was associated with older age (>35 years old). We did not observe correlation between CTS symptoms, abnormal NCS, positive Tinel's sign or Phalen's test. CONCLUSION: The prevalence of CTS symptoms was not high among the group of male VDT workers studied. Job seniority, but not specific tasks, was associated with CTS symptoms. More reliable and valid methods to quantify the ergonomic exposure are needed to establish the association of VDT tasks and CTS.

Adult↗

Central nervous system effects and visual fatigue in VDT workers.

To assess central nervous system effects and visual fatigue induced by work with visual display terminals (VDT), symptom frequency was assessed and visual evoked potential (VEP), critical flicker fusion (CFF) and near-point distance were measured in 24 female keypunchers before and after 2.5 h of VDT work and in 6 non-VDT-exposed subjects at the same intervals. Each keypuncher had been engaged in data entry for 1-7 (mean, 4) years. After VDT work, the number of complaints of subjective fatigue as well as an objective measure of near-point distance were significantly increased as compared with those before work; also, the N75, P100 and N145 latencies of VEP were significantly prolonged. The change of P100 latency during VDT work was inversely correlated with the number of years worked in data entry. No significant change was seen in any of these tests in the non-VDT-exposed subjects. The changes in N75 latency and subjective fatigue related to drowsiness and dullness in the keypunchers were significantly larger than those in the non-VDT-exposed subjects. The CFF was significantly lower in keypunchers than in non-VDT-exposed subjects in both the first and the second tests. These data suggest that VDT work is associated with impairment of the visual nervous system function, that VEP latencies appear to be a sensitive indicator of visual fatigue, at least transiently, and that CFF appears to be a good parameter for estimations of chronic visual fatigue.

Adolescent↗

Effects of residual astigmatism in contact lens wear on visual discomfort in VDT use.

The purpose of this study was to evaluate the effects of the residual astigmatism of contact lens wearers on the visual comfort of these individuals when using a video display terminal (VDT). We hypothesized that small amounts of uncorrected residual astigmatism of the type that is normally left uncorrected produce visual discomfort in the use of these devices even though visual acuity is relatively unaffected. Twelve subjects (ages 18 to 36 years) with corrected visual acuities of at least 20/25 (in each eye at distance with their contact lens correction) participated. All subjects were soft contact lens wearers who reported comfortable, well-adapted lens wear for a minimum of 1 year prior to the study. All subjects had between 0.50 and 1.00 D of residual astigmatism in each eye (mean = 0.68D). Our double-masked cross-over experiment included two 25-minute periods during which the subject read from a VDT. In a trial frame over their contact lens correction, the subjects were randomly assigned to wear either a test lens pair or a control lens pair (+0.12 DS) during the first period and the alternative pair during the second period. The test lens pair corrected all residual astigmatism (the over refraction). The control lens pair was considered a placebo. A questionnaire was used to obtain ratings of visual discomfort. Our analysis of the data indicated greater reported visual comfort for the test lens pair (Wilcoxon signed-rank test, p less than 0.01). These results suggest careful consideration be given to the correction of residual astigmatism of contact lens wearers who are VDT users.

Adolescent↗

Anxiety, musculoskeletal and visual disorders in video display terminal workers.

AIM: The increase in the working population assigned to video display terminals (VDT) has led to ever growing attention to reports on health effects. We studied musculoskeletal and visual disorders and levels of anxiety in 2 groups of VDT operators with different tasks, in order to evaluate if they could be influenced by organizational and intrinsically working factors. METHODS: The study included 190 VDT operators, subdivided into 2 groups (A and B) on the basis of tasks performed and average hours/ week spent at VDT (25 vs 36), and 190 controls not assigned to VDT. Ocular and musculoskeletal subjective symptoms and objective findings were assessed for all subjects, and the State-Trait Anxiety Inventory (STAI) test was administered. RESULTS: For VDT operators of the 2 groups, the relationship between ocular and musculoskeletal symptoms and findings, working life (P=0.0001) and number of hours spent at the VDT (symptoms P=0.001 and P=0.0001; findings P=0.002 and P=0.007), was significant. Group B VDT operators showed significantly higher state anxiety (S-anxiety) levels vs those in Group A and controls (P=0.001); trait anxiety (T-anxiety) was significantly higher in Group B and controls vs Group A (P=0.001 and P=0.03). CONCLUSIONS: Our results confirm the literature data about musculoskeletal and visual disorders and, as for anxiety, seem to denote a higher relevance of factors related to labor organization vs VDT use per se.

Adult↗