Color vision and occupational chemical exposures: I. An overview of tests and effects

Low-level occupational exposure to BTEX and dyschromatopsia: a systematic review and meta-analysis

Objectives. The present study aimed to assess whether occupational exposure to low concentrations of benzene, toluene, ethylbenzene and xylene (BTEX) is associated with color vision impairment. Methods. We queried PubMed, Scopus, Embase, Web of Science and ProQuest as the main databases, as well as gray literature such as Google Scholar. A random-effects model was used to assess relative risk. A funnel plot was created to assess publication bias. Meta-regression analysis was applied to identify variables that explain the between-study variation in the reported risk estimate. Results. An overall standardized mean difference of 0.529 (95% confidence interval [0.269, 0.788]; p < 0.0001) was obtained in the random-effects model, which corresponded to a medium-size effect. Duration and the levels of exposure to benzene, toluene and xylene were the significant predictors of the magnitude of the combined risk estimate. Chronic exposure to low levels of BTEX was associated with dyschromatopsia determined by the color confusion index. Conclusions. The impairments can occur even at exposures lower than the occupational exposure limits of BTEX. However, there are several flaws in the determination of workers' exposure, which did not allow to establish how low a level of these chemicals can cause color vision impairment.

Modeling D15 test sequences in red-green anomalous trichromacy

Color arrangement tests such as the D15 test can be used to detect congenital and acquired color vision defects. However, the D15 test cannot be used as the only test to assess color vision because of its relatively low sensitivity in less severe cases of color vision deficiency. In this study, we attempted to determine D15 cap arrangements for red/green anomalous trichromats with varying degrees of severity of color vision deficiency. The color coordinates of D15 test caps corresponding to a particular type and severity of color vision deficiency were determined using the model proposed by Yaguchi et al. [J. Opt. Soc. Am. A35, B278 (2018)JOAOD60740-323210.1364/JOSAA.35.00B278]. The arrangement of the color caps was modeled by assuming that individuals with color vision deficiency would arrange the D15 test caps judging by color differences perceived by them. The proposed simulation correctly predicts the increase in severity of color vision deficiency with spectral reduction between the L- and M-cone photopigments. The type of color vision deficiency is correctly predicted with few exceptions in protanomalous trichromats.

An inadvertent issue of human retina exposure to endocrine disrupting chemicals: A safety assessment

Endocrine disrupting chemicals (EDCs) are a group of chemical compounds that present a considerable public health problem due to their pervasiveness and associations with chronic diseases. EDCs can interrupt the endocrine system and interfere with hormone homeostasis, leading to abnormalities in human physiology. Much attention has been focused on the adverse effects EDCs have on the reproductive system, neurogenesis, neuroendocrine system, and thyroid dysfunction. The eye is usually directly exposed to the surrounding environment; however, the influences of EDCs on the eye have received comparatively little attention. Ocular diseases, such as ocular surface diseases and retinal diseases, have been implicated in hormone deficiency or excess. Epidemiologic studies have shown that EDC exposure not only causes ocular surface disorders, such as dry eye, but also associates with visual deficits and retinopathy. EDCs can pass through the human blood-retinal barrier and enter the neural retina, and can then accumulate in the retina. The retina is an embryologic extension of the central nervous system, and is extremely sensitive and vulnerable to EDCs that could be passed across the placenta during critical periods of retinal development. Subtle alterations in the retinal development process usually result in profound immediate, long-term, and delayed effects late in life. This review, based on extensive literature survey, briefly summarizes the current knowledge about the impact of representative manufactured EDCs on retinal toxicity, including retinal structure alterations and dysfunction. We also highlight the potential mechanism of action of EDCs on the retina, and the predictive retinal models of EDC exposure.

Prevalence of Color Vision Deficiency in an Adult Population in South Korea

SIGNIFICANCE

Large differences in failure rates for color vision screening have been reported among different regional groups. However, color vision deficiency prevalence in Korea has only been investigated within a small area of the country.

PURPOSE

This study examines the prevalence of failing a color vision screening and its sex-related differences using a sample that is representative of the whole Korean population.

METHODS

This population-based cross-sectional study evaluated 2686 subjects (age, 19 to 49 years) who participated in the sixth Korea National Health and Nutrition Examination Survey (2013). Color vision deficiency was assessed using the Hardy-Rand-Rittler (HRR) test by an ophthalmologist. According to standard criteria for the HRR, it classified each subject as color normal, protan, deutan, tritan, or unclassified color vision loss. All participants had comprehensive medical evaluations and ocular history taken.

RESULTS

The weighted overall prevalence of color vision deficiency in the Korean population was 3.9% (95% confidence interval, 3.0 to 5.4%). The prevalence of color vision deficiency was higher in male participants (6.5%) than in female participants (1.1%). Among all participants, deutan deficiency (2.5%) had a higher prevalence than did protan deficiency (0.4%). For male participants who failed the HRR screening, deutan-type deficiency was detected most often (64.2%), whereas an unclassified color vision deficiency type was the most common (52.9%) among female participants who failed the HRR screening. As expected, male participants were more likely to fail the HRR screening compared with female participants (prevalence ratio, 6.08; 95% confidence interval, 3.61 to 10.26).

CONCLUSIONS

This large population-based study of color vision deficiency among Koreans gives the most accurate estimate of failing a color vision screening test to date and provides useful information for planning adaptive strategies.

The neuro-ophthalmological effects related to long-term occupational exposure to organic solvents in painters

PURPOSE

Organic solvents are widely used in many industries, and usually, exposure occurs with mixtures of solvents. Organic solvent mixtures are known for their ability to affect tissues of high lipid content including the myelin sheath in the nervous system. The purpose of this work was to study the evidence that long-term (more than 10 years) exposure to organic solvent mixtures among painters can induce neuro-ophthalmological effects on the function of retinal ganglion cells and the optic tract.

METHODS

Twenty workers with long-term occupational exposure to mixed organic solvents were compared to 40 control subjects. The controls were matched for age, gender, and demographic characteristics but were not occupationally exposed to any known organic solvents, using the following comparators: visual evoked potential (VEP), electroretinogram (ERG), color vision (CV), and contrast sensitivity (CS) testing. Environmental monitoring was done in the work environment with consideration to the American Conference of Governmental Industrial Hygienists Threshold Limit Values (ACGIH-TLVs).

RESULTS

The exposed group had significantly longer latency and higher amplitude of VEP waves especially P100, higher Color Confusion Index (CCI), especially affecting the blue-yellow spectrum, and lower Log CS. There was no significant difference between exposed and nonexposed groups in full-field flash ERG response; however, in the pattern ERG, the exposed group had significantly longer latency of P50, which reflects changes in the retinal ganglion cell.

CONCLUSION

Long-term occupational exposure to mixed organic solvents appeared to affect the optic tract functions in the form of increasing latency of VEP response, affecting the quality of CV and decreasing CS. It also affects the retinal ganglion cell layer with increased latency of P50 of the pattern ERG response.

Impaired colour vision in workers exposed to organic solvents: A systematic review

OBJECTIVE

To evaluate recent evidence concerning the relationship between the exposure to organic solvents and the impairment of colour vision.

METHODS

A bibliographic search was conducted for scientific papers published in the last 15 years, in the LILACS, PubMed, Science Direct, EBSCO, and Cochrane databases that included observational studies assessing the relationship between impairment in colour vision and exposure to organic solvents.

RESULTS

Eleven studies were selected that were performed on an economically active population and used the Lanthony D-15 desaturated test (D-15d), measured the exposure to organic solvents, and included unexposed controls. It was found that there is a statistically significant relationship between the exposure to organic solvents and the presence of an impairment in colour vision.

CONCLUSIONS

The results support the hypothesis that exposure to organic solvents could induce acquired dyschromatopsia. The evaluation of colour vision with the D-15d test is simple and sensitive for diagnosis. More studies need to be conducted on this subject in order to better understand the relationship between impaired colour vision and more severe side effects caused by this exposure.

Acquired Color Vision Defects and Hexane Exposure: A Study of San Francisco Bay Area Automotive Mechanics

Occupational exposure to solvents, including n-hexane, has been associated with acquired color vision defects. Blue-yellow defects are most common and may be due to neurotoxicity or retinal damage. Acetone may potentiate the neurotoxicity of n-hexane. We present results on nonhexane solvent and hexane exposure and color vision from a cross-sectional study of 835 automotive repair workers in the San Francisco Bay Area, California (2007-2013). Cumulative exposure was estimated from self-reported work history, and color vision was assessed using the Lanthony desaturated D-15 panel test. Log-binomial regression was used to estimate prevalence ratios for color vision defects. Acquired color vision defects were present in 29% of participants, of which 70% were blue-yellow. Elevated prevalence ratios were found for nonhexane solvent exposure, with a maximum of 1.31 (95% confidence interval (CI): 0.86, 2.00) for blue-yellow. Among participants aged ≤50 years, the prevalence ratio for blue-yellow defects was 2.17 (95% CI: 1.03, 4.56) in the highest quartile of nonhexane solvent exposure and 1.62 (95% CI: 0.97, 2.72) in the highest category of exposure to hexane with acetone coexposure. Cumulative exposures to hexane and nonhexane solvents in the highest exposure categories were associated with elevated prevalence ratios for color vision defects in younger participants.

Toluene inhalation exposure for 13 weeks causes persistent changes in electroretinograms of Long-Evans rats

Studies of humans chronically exposed to volatile organic solvents have reported impaired visual functions, including low contrast sensitivity and reduced color discrimination. These reports, however, lacked confirmation from controlled laboratory experiments. To address this question experimentally, we examined visual function by recording visual evoked potentials (VEP) and/or electroretinograms (ERG) from four sets of rats exposed repeatedly to toluene. In addition, eyes of the rats were examined with an ophthalmoscope and some of the retinal tissues were evaluated for rod and M-cone photoreceptor immunohistochemistry. The first study examined rats following exposure to 0, 10, 100 or 1000ppm toluene by inhalation (6hr/d, 5d/wk) for 13 weeks. One week after the termination of exposure, the rats were implanted with chronically indwelling electrodes and the following week pattern-elicited VEPs were recorded. VEP amplitudes were not significantly changed by toluene exposure. Four to five weeks after completion of exposure, rats were dark-adapted overnight, anesthetized, and several sets of electroretinograms (ERG) were recorded. In dark-adapted ERGs recorded over a 5-log (cd-s/m(2)) range of flash luminance, b-wave amplitudes were significantly reduced at high stimulus luminance values in rats previously exposed to 1000ppm toluene. A second set of rats, exposed concurrently with the first set, was tested approximately one year after the termination of 13 weeks of exposure to toluene. Again, dark-adapted ERG b-wave amplitudes were reduced at high stimulus luminance values in rats previously exposed to 1000ppm toluene. A third set of rats was exposed to the same concentrations of toluene for only 4 weeks, and a fourth set of rats exposed to 0 or 1000ppm toluene for 4 weeks were tested approximately 1year after the completion of exposure. No statistically significant reductions of ERG b-wave amplitude were observed in either set of rats exposed for 4 weeks. No significant changes were observed in ERG a-wave amplitude or latency, b-wave latency, UV- or green-flicker ERGs, or in photopic flash ERGs. There were no changes in the density of rod or M-cone photoreceptors. The ERG b-wave reflects the firing patterns of on-bipolar cells. The reductions of b-wave amplitude after 13 weeks of exposure and persisting for 1year suggest that alterations may have occurred in the inner nuclear layer of the retina, where the bipolar cells reside, or the outer or inner plexiform layers where the bipolar cells make synaptic connections. These data provide experimental evidence that repeated exposure to toluene may lead to subtle persistent changes in visual function. The fact that toluene affected ERGs, but not VEPs, suggests that elements in the rat retina may be more sensitive to organic solvent exposure than the rat visual cortex.

Acquired color vision deficiency

Acquired color vision deficiency occurs as the result of ocular, neurologic, or systemic disease. A wide array of conditions may affect color vision, ranging from diseases of the ocular media through to pathology of the visual cortex. Traditionally, acquired color vision deficiency is considered a separate entity from congenital color vision deficiency, although emerging clinical and molecular genetic data would suggest a degree of overlap. We review the pathophysiology of acquired color vision deficiency, the data on its prevalence, theories for the preponderance of acquired S-mechanism (or tritan) deficiency, and discuss tests of color vision. We also briefly review the types of color vision deficiencies encountered in ocular disease, with an emphasis placed on larger or more detailed clinical investigations.

Exposure to organic solvents used in dry cleaning reduces low and high level visual function

PURPOSE

To investigate whether exposure to occupational levels of organic solvents in the dry cleaning industry is associated with neurotoxic symptoms and visual deficits in the perception of basic visual features such as luminance contrast and colour, higher level processing of global motion and form (Experiment 1), and cognitive function as measured in a visual search task (Experiment 2).

METHODS

The Q16 neurotoxic questionnaire, a commonly used measure of neurotoxicity (by the World Health Organization), was administered to assess the neurotoxic status of a group of 33 dry cleaners exposed to occupational levels of organic solvents (OS) and 35 age-matched non dry-cleaners who had never worked in the dry cleaning industry. In Experiment 1, to assess visual function, contrast sensitivity, colour/hue discrimination (Munsell Hue 100 test), global motion and form thresholds were assessed using computerised psychophysical tests. Sensitivity to global motion or form structure was quantified by varying the pattern coherence of global dot motion (GDM) and Glass pattern (oriented dot pairs) respectively (i.e., the percentage of dots/dot pairs that contribute to the perception of global structure). In Experiment 2, a letter visual-search task was used to measure reaction times (as a function of the number of elements: 4, 8, 16, 32, 64 and 100) in both parallel and serial search conditions.

RESULTS

Dry cleaners exposed to organic solvents had significantly higher scores on the Q16 compared to non dry-cleaners indicating that dry cleaners experienced more neurotoxic symptoms on average. The contrast sensitivity function for dry cleaners was significantly lower at all spatial frequencies relative to non dry-cleaners, which is consistent with previous studies. Poorer colour discrimination performance was also noted in dry cleaners than non dry-cleaners, particularly along the blue/yellow axis. In a new finding, we report that global form and motion thresholds for dry cleaners were also significantly higher and almost double than that obtained from non dry-cleaners. However, reaction time performance on both parallel and serial visual search was not different between dry cleaners and non dry-cleaners.

CONCLUSIONS

Exposure to occupational levels of organic solvents is associated with neurotoxicity which is in turn associated with both low level deficits (such as the perception of contrast and discrimination of colour) and high level visual deficits such as the perception of global form and motion, but not visual search performance. The latter finding indicates that the deficits in visual function are unlikely to be due to changes in general cognitive performance.

Retinal and visual system: occupational and environmental toxicology

Occupational chemical exposure often results in sensory systems alterations that occur without other clinical signs or symptoms. Approximately 3000 chemicals are toxic to the retina and central visual system. Their dysfunction can have immediate, long-term, and delayed effects on mental health, physical health, and performance and lead to increased occupational injuries. The aims of this chapter are fourfold. First, provide references on retinal/visual system structure, function, and assessment techniques. Second, discuss the retinal features that make it especially vulnerable to toxic chemicals. Third, review the clinical and corresponding experimental data regarding retinal/visual system deficits produced by occupational toxicants: organic solvents (carbon disulfide, trichloroethylene, tetrachloroethylene, styrene, toluene, and mixtures) and metals (inorganic lead, methyl mercury, and mercury vapor). Fourth, discuss occupational and environmental toxicants as risk factors for late-onset retinal diseases and degeneration. Overall, the toxicants altered color vision, rod- and/or cone-mediated electroretinograms, visual fields, spatial contrast sensitivity, and/or retinal thickness. The findings elucidate the importance of conducting multimodal noninvasive clinical, electrophysiologic, imaging and vision testing to monitor toxicant-exposed workers for possible retinal/visual system alterations. Finally, since the retina is a window into the brain, an increased awareness and understanding of retinal/visual system dysfunction should provide additional insight into acquired neurodegenerative disorders.

A case of bilateral, acquired, and acute dysfunction of short-wavelength-sensitive cone systems

To report a case of bilateral, acquired, and acute dysfunction of short-wavelength-sensitive (SWS) cone systems. The case was a healthy 39-year-old man. He noticed sudden onset of bilateral abnormal color vision. Ophthalmic examinations revealed normal fundi in both eyes. Farnsworth panel D-15 test and Farnsworth-Munsell 100-hue test showed tritanopia. White-on-white static perimetry showed no abnormality; however, blue-on-yellow static perimetry detected remarkably reduced sensitivity at the lower visual field in both eyes. ISCEV-standard full-field electroretinograms (ERGs) were normal; however, blue-on-yellow ERGs showed reduced amplitude of b-wave that was derived from SWS cone systems in both eyes. He was observed for 1 year, and no improvement in color vision was found during the observation. This is a unique case which showed bilateral, acquired, and acute dysfunction of SWS cone systems. The cause of the acquired tritanopia remains to be known.

Psychophysical evaluation of achromatic and chromatic vision of workers chronically exposed to organic solvents

The purpose of this paper was to evaluate achromatic and chromatic vision of workers chronically exposed to organic solvents through psychophysical methods. Thirty-one gas station workers (31.5 ± 8.4 years old) were evaluated. Psychophysical tests were achromatic tests (Snellen chart, spatial and temporal contrast sensitivity, and visual perimetry) and chromatic tests (Ishihara's test, color discrimination ellipses, and Farnsworth-Munsell 100 hue test—FM100). Spatial contrast sensitivities of exposed workers were lower than the control at spatial frequencies of 20 and 30 cpd whilst the temporal contrast sensitivity was preserved. Visual field losses were found in 10–30 degrees of eccentricity in the solvent exposed workers. The exposed workers group had higher error values of FM100 and wider color discrimination ellipses area compared to the controls. Workers occupationally exposed to organic solvents had abnormal visual functions, mainly color vision losses and visual field constriction.

Review of the epidemiologic literature on residential exposure to perchloroethylene

Perchloroethylene is a solvent that is widely used for dry cleaning. There has been considerable interest in the toxicity of this chemical because of the potential for low-level exposure among a large portion of the US population. Although substantial epidemiologic literature exists on high-level occupational exposure to perchloroethylene, there are relatively few studies dealing with lower-level residential exposure. In the current paper, the author reviews this limited residential literature, with special emphasis on strengths, limitations, and consistency. Reviewed studies primarily address neurobehavioral, cancer, and reproductive endpoints. Most studies used an ecological or cross-sectional design, with exposure defined by either drinking-water contamination or proximity to dry cleaning. In general, reviewed studies were highly exploratory, with inconsistencies and potential for bias that detract from interpretation of study findings. The magnitudes of reported effects are frequently incompatible with the effects reported from much higher occupational and human-chamber exposures. Overall, few reliable conclusions can be drawn from this sparse and highly limited body of literature.

Evaluation of multiple neurotoxic outcomes in cancer chemotherapy

Although it is now clear that cognitive dysfunction is a common accompaniment of cancer chemotherapy, its implications await further research and direction. Most of the clinical research relies on standard neuropsychological tests that were developed to diagnose stable traits. Cognitive dysfunction in patients undergoing treatment varies with time, however. Its dimensions will vary during the course of treatment, which generally consists of cycles of drug administration followed by recovery periods. To effectively determine the connection between chemotherapy and cognitive function requires neuropsychological tests based on performance, so that they can be administered repeatedly at specified times during the entire course of treatment and beyond. A number of computerized test batteries, many of which have been developed for environmental neurotoxicology, are now available that fit such criteria. Moreover, cognitive impairment is only one aspect of chemotherapy-induced neurotoxicity. A full appreciation of its scope requires assessment of sensory functions such as vision, audition and somatosensory properties and assessment of motor function. A program of research based on animal models is also essential. Only with animal models is it possible to determine dose-response relationships and to couple behavioral with mechanistic indices such as neuroplasticity. Animal behavior models play a vital role in environmental toxicology because, from them, it is possible to derive some index of exposure that limits adverse effects. However, as in human testing, it is critical to choose situations whose properties remain stable over long periods of time so as to trace the time course of neurotoxicity. Schedule-controlled operant behavior offers the most promising source of animal models.

Differential effects of inhaled toluene on locomotor activity in adolescent and adult rats

Inhalant abuse is a world-wide public health concern among adolescents. Most preclinical studies have assessed inhalant effects in adult animals leaving unclear how behavioral effects differ in younger animals. We exposed adolescent (postnatal day [PN] 28) and adult (PN90) male rats to toluene using 1 of 3 exposure patterns. These patterns modeled those reported in toluene abuse in teens and varied concentration, number and length of exposures, as well as the inter-exposure interval. Animals were exposed repeatedly over 12 days to toluene concentrations of 0, 8000 or 16,000 parts per million (ppm). Locomotor activity was quantified during toluene exposures and for 30 min following completion of the final daily toluene exposure. For each exposure pattern, there were significant toluene concentration-related increases and decreases in locomotor activity compared to the 0-ppm "air" controls at both ages. These changes depended upon when activity was measured - during or following exposure. Compared to adults, adolescents displayed greater locomotor activity on the first day and generally greater increases in activity over days than adults during toluene exposure. Adults displayed greater locomotor activity than adolescents in the "recovery" period following exposure on the first and subsequent days. Age group differences were clearest following the pattern of paced, brief (5-min) repeated binge exposures. The results suggest that locomotor behavior in rats during and following inhalation of high concentrations of toluene depends on age and the pattern of exposure. The results are consistent with dose-dependent shifts in sensitivity and sensitization or tolerance to repeated toluene in the adolescent animals compared to the adult animals. Alternate interpretations are possible and our interpretation is limited by the range of very high concentrations of toluene used. The results imply that both pharmacological and psychosocial factors contribute to the teen prevalence of inhalant abuse.

Toluidine blue color perception in identification of oral mucosal lesions

The objective of this study is to examine observer agreement on the rank of the color tones after toluidine blue staining of a mucosal lesion. Cohort study with repeated measures is the design of the study. Twenty observers ranked and scored 8 specified areas on the color images of a lesion before and after toluidine blue application in two sessions. Inter and intra-observer variations were analyzed with Cohen's kappa. The L* (the black-white axis), a* (red-green axis), and b* (yellow-blue axis) values were measured and set as the gold standards. Intra and inter-observer agreements were к = 0.86 and к = 0.854. All color parameters were effective on the color ranking order (pL* = 0.00, pa* = 0.007, pb* = 0.00), although L* and b* were more effective on the ranking of the samples than a*. Areas that appeared pale blue visually had a significant blue component, but the observers were confused with the effect of whiteness of the area in clinical decision making.

The eye--a neglected organ in environmental and occupational medicine: an overview of known environmental and occupational non-traumatic effects on the eyes

The objective of this study was to give an overview of the known literature data on the influence of environmental and occupational factors on the eye. Sixty-six articles were selected by searching Medline and PubMed databases using the following key words in different combinations: occupational and environmental factors, dry eye syndrome, cataract, retinal vascular changes. Most of the studies dealt with conditions on the eye surface and used eye discomfort syndrome and dry eye syndrome to outline the effects of air pollutants. Some reported increased frequency of lens opacities due to indoor fuel exposure, in particular biofuel, and negative effects of styrene exposure on colour vision. Investigations of retinal vascular changes and retinopathy after chronic exposure to carbon disulfide (CS2) and of retinal and choroidal haemodynamics after exposure to carbon monoxide (CO) found that CS2 caused an increase in retinal venous diameters and CO caused an increase in arterial and venous diameters, retinal blood flow velocity, and fundus pulsation amplitude. This article also discusses the influence of light exposure on retinal damage. It shows that very little information is available about the influence of environmental and occupational factors on the eye, and retina and retinal vessels in particular.

Color vision panel tests: a metric for interpreting numeric analytic indices

PURPOSE

Various systems have been proposed for quantifying arrangements of colored caps in panel tests of color vision. We examine Vingrys and King-Smith's (Vingrys and King-Smith. Invest Ophthalmol Vis Sci 1988;29:50-63) computed values for their different numerical indices derived and propose a metric for interpreting these index values. Our approach is based on performance of color-normals when angular subtenses of the panel caps are reduced by changing the test distance.

METHODS

Seven participants with normal color vision performed the panel tests at each of five viewing distances from 0.5 to 7.56 m (chromatic portions of the caps subtending 75 to 5 minarc). To obtain cutoff values for the numeric indices at the standard viewing distance under our viewing conditions, we also tested 69 unselected, volunteers with the Farnsworth D-15 and Lanthony desaturated D-15 panels. From each participant one eye, usually the worse, was included in analyses to find the 90th percentiles for each index, which we used as cutoff values. Many of the participants also made Rayleigh anomaloscope matches.

RESULTS

For normal observers, values for the C-index (confusion) and for the S-index (polarity of an individual's pattern of cap reversals) begin to worsen when viewing distance increases beyond 2 m (corresponding to a subtense of 15 minarc). Thereafter, increasing values of the indices (deteriorations in color vision) fall exponentially with distance. We find that the functions for the Farnsworth and Lanthony panels are so highly correlated that the same function can be used for both. The cutoff index values for our conditions, values that differ little from those reported by others, correspond to a viewing distance of about 2.5 to 3.0 m.

CONCLUSIONS

An individual's color vision performance can be interpreted by relating it to performance of color-normals viewing the test caps at some non-standard distance. This is similar to Snellen notation for acuity.

Reference intervals and discrimination values of the Lanthony desaturated D-15 panel test in young to middle-aged Japanese army officials: the Okubo Color Study Report 1

PURPOSE

To better understand the reference values and adequate discrimination values of colour vision function with described quantitative systems for the Lanthony desaturated D-15 panel (D-15DS).

METHODS

A total of 1042 Japanese male officials were interviewed and underwent testing using Ishihara pseudoisochromatic plates, standard pseudoisochromatic plates part 2, and the D-15DS. The Farnsworth-Munsell (F-M) 100-hue test and the criteria of Verriest et al were used as definitive tests. Outcomes of the D-15DS were calculated using Bowman's Colour Confusion Index (CCI). The study design included two criteria. In criterion A, subjects with current or past ocular disease and a best-corrected visual acuity less than 0.7 on a decimal visual acuity chart were excluded. In criterion B, among subjects who satisfied criterion A, those who had a congenital colour sense anomaly were excluded.

RESULTS

Overall, the 90th percentile (95th percentile) CCI values for criteria A and B in the worse eye were 1.70 (1.95) and 1.59 (1.73), respectively. In subjects satisfying criterion B, the area under the receiver operating characteristic curve was 0.951 (95% confidence interval, 0.931-0.971). The CCI discrimination values of 1.52 or 1.63 showed 90.3% sensitivity and 90% specificity, or 71.5% sensitivity and 95% specificity, respectively, for discriminating acquired colour vision impairment (ACVI).

CONCLUSION

We provided the 90th and 95th percentiles in a young to middle-aged healthy population. The CCI is in good agreement with the diagnosis of ACVI. Our results could be helpful for using D-15DS for screening purposes.

Chemobrain: a translational challenge for neurotoxicology

Neurotoxicity is a frequent accompaniment of cancer chemotherapy, and held by many oncologists to be the major dose-limiting side effect. It appears in many forms, but attracted attention during the past decade primarily because of complaints by patients of impaired cognitive function they have labeled as "chemobrain". Neuropsychological testing confirmed the validity of these complaints and has generated a substantial literature examining different aspects of cognitive impairment in various clinical populations undergoing a variety of treatments. Cognitive impairment is far from the only manifestation of neurotoxicity induced by chemotherapy, however. It alters sensory function and motor function as well. A critical need for patients is a suite of methods that will enable clinicians to trace the onset and progression of neurotoxicity so as to guide and balance decisions about the course of chemotherapy. This commentary describes some of the potential methods and encourages neurotoxicologists to enlist their unique skills in the service of these needs.

Nerve conduction, visual evoked responses and electroretinography in tunnel workers previously exposed to acrylamide and N-methylolacrylamide containing grouting agents

The study examines possible persisting effects on the peripheral nervous system and visual system in tunnel workers previously exposed to acrylamide and N-methylolacrylamide during grouting work. We compared neurophysiological function in 44 tunnel workers previously exposed during grouting operations (2-10 years post exposure), with 49 tunnel workers with no history of exposure to acrylamide. Nerve conduction velocities (NCV), distal delay, F-response and amplitude in median and ulnar nerves of the right arm, peroneal, sural and tibial nerves of the right leg, visual evoked response (VER) and electroretinography (ERG) were measured. VER and ERG were also performed in 24 subjects more recently exposed to acrylamide grout (16 months post exposure). Exposure to acrylamide containing grouts was assessed by questionnaires. A statistically significant reduction in the mean sensory NCV of the sural nerve (p=0.005), as well as a non-significant reduction of sural amplitude was found in the previously exposed group compared to the control group. VER latencies to the onset of the occipital potential (N75) were prolonged in both exposed groups compared to the control group (p<0.05). ERG 30 Hz flicker amplitude was reduced in the recently exposed group compared to the referents (p<0.05). The results indicate slight subclinical, but persistent toxic effects in the sural nerve and the visual system in tunnel workers exposed to N-methylolacrylamide and acrylamide during grouting operations.

Colour vision and light sensitivity in tunnel workers previously exposed to acrylamide and N-methylolacrylamide containing grouting agents

OBJECTIVES

The aim of the study was to examine possible persisting visual system effects in tunnel workers previously exposed to acrylamide and N-methylolacrylamide during grouting work.

MATERIAL AND METHODS

Visual field light sensitivity threshold and colour vision has been examined among 44 tunnel workers 2-10 years after exposure to acrylamide and N-methylolacrylamide containing grouting agents. Forty-four tunnel workers not involved in grouting operations served as control group. Information on exposure and background variables was obtained for all participants from a questionnaire. Visual light sensitivity threshold was measured using Humphrey Visual Field Static Perimeter 740, program 30-2 Fastpack, with red stimuli on white background, and colour vision, using Lanthony D-15 Desaturated Color test. Based on D-15d test results, colour confusion index (CCI), and a severity index (C-index) was calculated.

RESULTS

The exposed group had a significantly higher threshold for detecting single stimuli in all parts of the inner 30 degrees of the visual field compared to the control group. The foveal threshold group difference was 1.4 dB (p=0.002) (mean value, both eyes). On the Lanthony 15 Hue Desaturated test, the exposed subjects made more errors in sorting blue colours, and a statistically significant increase in C-index was observed. Surrogate measures for duration and intensity of exposure gave no further improvement of the model.

CONCLUSIONS

The results indicate slightly reduced light sensitivity and reduced colour discrimination among the exposed subjects compared to the controls. The findings may be due to previous exposure to acrylamide containing grouts among the tunnel workers.

Colour vision defects in occupational chronic solvent encephalopathy

Occupational chronic solvent encephalopathy (CSE) is associated with a number of neurobehavioural disorders including defects of visual perception. The purpose of this study was to characterize colour vision defects in CSE patients. Colour vision was tested in bright illumination with the Farnsworth-Munsell 100-hue test in workers who had CSE due to occupational exposure to common industrial solvents. Before assessing colour vision, the subjects' ocular health and visual functions were evaluated. On the basis of this evaluation, 36 subjects with healthy eyes were selected and their colour vision was tested monocularly. The colour vision performance of the patient group was, statistically, significantly inferior to that of a control group matched by age at a group level. A mixed form of reduced colour sensitivity was found in 42% (n=15/36) of the cases, affecting the entire range of Munsell hues. No association was found between the length and intensity of exposure and colour vision performance. Our results show that CSE patients can have significantly impaired colour discrimination ability, although their eyes are healthy and their other visual functions are normal. This may indicate toxic damage to higher level visual processing, possibly the colour selective regions of the cerebral cortex.

Visual search and eye movements in patients with chronic solvent-induced toxic encephalopathy

Various aspects of visual perception have been found to be impaired in patients with occupational chronic solvent-induced toxic encephalopathy (CSE). The purpose of the study was to characterise the changes in eye movements and visual search performance in CSE patients. We measured eye movements of 13 CSE patients and 22 healthy controls during dynamic visual search task by using a fast video eye tracker. The task was to search for and identify a target letter among numerals presented in a rectangular stimulus matrix (3x3-10x10 items). Threshold search time, i.e. the duration of stimulus presentation required for identifying the target with a given probability was determined by using a psychophysical staircase method. The visual search times of the CSE patients were clearly longer, and they needed considerably more eye fixations than healthy controls to find the target. Thus, their reduced performance in this task was mainly related to the reduction in the number of items which could be processed during a single eye fixation (perceptual span). This reduction probably reflects a limited capacity of visual attention, since visual acuity, contrast sensitivity, and the oculomotor saccade velocity were found to be normal. The results suggest that motor slowness or low-level visual factors do not explain the poor performance of CSE patients in visual search tasks. The results are also discussed with respect to the effects of education, and compared to the performance in the widely used neuropsychological Trail Making Test, which uses similar stimuli and requires visual search.

Color naming deficits and attention-deficit/hyperactivity disorder: a retinal dopaminergic hypothesis

BACKGROUND

Individuals with Attention-Deficit/Hyperactive Disorder (ADHD) have unexplained difficulties on tasks requiring speeded processing of colored stimuli. Color vision mechanisms, particularly short-wavelength (blue-yellow) pathways, are highly sensitive to various diseases, toxins and drugs that alter dopaminergic neurotransmission. Thus, slow color processing might reflect subtle impairments in the perceptual encoding stage of stimulus color, which arise from hypodopaminergic functioning.

PRESENTATION OF HYPOTHESES

1) Color perception of blue-yellow (but not red-green) stimuli is impaired in ADHD as a result of deficient retinal dopamine; 2) Impairments in the blue-yellow color mechanism in ADHD contribute to poor performance on speeded color naming tasks that include a substantial proportion of blue-yellow stimuli; and 3) Methylphenidate increases central dopamine and is also believed to increase retinal dopamine, thereby normalizing blue-yellow color perception, which in turn improves performance on the speeded color naming tasks.

TESTING THE HYPOTHESIS

Requires three approaches, including:1) direct assessment of color perception in individuals with ADHD to determine whether blue-yellow color perception is selectively impaired; 2) determination of relationship between performance on neuropsychological tasks requiring speeded color processing and color perception; and 3) randomized, controlled pharmacological intervention with stimulant medication to examine the effects of enhancing central dopamine on color perception and task performance

IMPLICATIONS OF HYPOTHESIS

If substantiated, the findings of color perception problems would necessitate a re-consideration of current neuropsychological models of attention-deficit/hyperactivity disorder, guide psycho-education, academic instruction, and require consideration of stimulus color in many of the widely used neuropsychological tests.

The reliability of the Lanthony Desaturated D-15 test

PURPOSE

The Lanthony Desaturated Panel D-15 has been used to measure fine color discrimination for congenital and acquired color vision defects. This study investigated the test-retest reliability of the test using an intertest interval of approximately 1 month.

METHODS

One hundred twenty-six color vision normals (mean age = 34.5 years) were administered several color vision tests, including the Lanthony Desaturated D-15. Normal color vision status was confirmed using the anomaloscope and HRR color plates. The color vision tests were readministered 3 to 6 weeks after initial testing. The results of the Lanthony test were expressed using the color confusion index of Bowman. The difference in Color Confusion Index (CCI) between the two administrations was calculated and used to determine the intraclass correlation coefficient.

RESULTS

The overall mean CCI for the two administrations for these subjects was 1.11 +/- 0.136. The mean difference in CCI score between test administrations was -0.02 +/- 0.128. There was a strong correlation between the absolute value of the difference in CCI and the mean CCI for each subject (r = 0.51, p < 0.0001). The intraclass correlation coefficient was 0.56 (95% confidence interval, 0.43-0.67).

CONCLUSIONS

Although the Lanthony Desaturated D-15 test can be used to assess fine color discrimination, there is considerable within-subject variability in test results. The intraclass correlation coefficient is less than that recommended for use in clinical testing or research. Clinicians should consider at least three administrations of the test at each sitting to ensure precision and we recommend taking the mean of those three tests.

Vision abnormalities in young children exposed prenatally to organic solvents

Despite an accumulating body of evidence demonstrating that the visual system is an important target for organic solvent toxicity in adults, little attention has been paid to the visual functioning of children with prenatal exposure to organic solvents. The present study aimed to: (1) determine prospectively whether prenatal solvent exposure increases the risk of visual deficits in infants and (2) assess the relationship between estimates of exposure level and integrity of visual responses. A sample of 21 infants born to women who were occupationally exposed to solvents during pregnancy was compared with 27 non-exposed age-matched control infants. All mothers were recruited from Motherisk, an antenatal counseling service in Toronto, Canada. Contrast sensitivity and grating acuity were assessed using a sweep visual evoked potential (VEP) technique whereas chromatic- and achromatic mechanisms were assessed using a transient VEP technique. Exposure level was estimated from questionnaire data obtained during pregnancy. Testers were masked to exposure status. Results showed a significant reduction in contrast sensitivity in the low and intermediate spatial frequency range in solvent-exposed infants compared to controls (p<0.001). With respect to grating acuity, there was a significant effect of exposure level, with children in the high exposed having reduced grating acuity compared with children in the low exposed group (p<0.025) and controls (p=0.02). Regarding color vision, 26.3% of infants in the exposed group versus 0% of the controls produced abnormal VEP responses to the red-green onset stimulus (p<0.01), but not to either blue-yellow or achromatic stimuli. No differences were found with respect to latency or amplitude of chromatic and achromatic response. These findings suggest that prenatal solvent exposure is associated with selective visual deficits, including reduced contrast sensitivity and abnormal red-green vision. Increasing levels of exposure may lead to further visual deficits affecting grating acuity. These findings support the need for a re-evaluation of current occupational exposure standards for pregnant women.

Homology of assessment of visual function in human and animal models

To connect animal models with human neurobehavioral evaluations, it is necessary to understand the level of homology present between tests administered across species. This paper identifies four different levels of homology of assessment based on identity of measurement, function, and underlying neural substrate. These are discussed using detailed examples from toxicology of the visual system, with additional examples from tests of motor and cognitive function. This should provide a framework for considering both animal to human extrapolation and human to animal extrapolation, that is, how to import human experimental epidemiology findings into the lab for further work investigating mechanisms of toxicity. Designing neurobehavioral or sensory evaluations that permit easier extrapolation between human and animal models is necessary if we are to develop testing strategies that take advantage of mechanistic information at whole animal, in vitro, proteonomic, or genomic levels.

Human neurobehavioral effects of long-term exposure to styrene: a meta-analysis

Many reports in the literature suggest that long-term exposure to styrene may exert a variety of effects on the nervous system, including increased choice reaction time and decreased performance of color discrimination and color arrangement tasks. Sufficient information exists to perform a meta-analysis of these observations quantifying the relationships between exposure (estimated from biomarkers) and effects on two measures of central nervous system function: reaction time and color vision. To perform the meta-analysis, we pooled data into a single database for each end point. End-point data were transformed to a common metric of effect magnitude (percentage of baseline). We estimated styrene concentration from biomarkers of exposure and fitted linear least-squares equations to the pooled data to produce dose-effect relationships. Statistically significant relationships were demonstrated between cumulative styrene exposure and increased choice reaction time as well as increased color confusion index. Eight work-years of exposure to 20 ppm styrene was estimated to produce a 6.5% increase in choice reaction time, which has been shown to significantly increase the probability of automobile accidents. The same exposure history was predicted to increase the color confusion index as much as 1.7 additional years of age in men.

Effects of long-term occupational solvent exposure on contrast sensitivity and performance in visual search

Sensitive and easily applicable screening tests are greatly needed for the early detection of nervous system dysfunction in people working with neurotoxic substances. Previous studies have shown that long-term solvent exposure may cause deficits in visual perception. We, therefore, studied the effects of long-term occupational solvent exposure and chronic encephalopathy on performance in three vision tests novel in the present context. Two visual search tasks were used: the letter search test measured the speed of finding a letter in an array of numerals, and the pop-out search test required the observer to detect the presence or absence of a tilted line segment in an array of vertical line segments. With the letter contrast sensitivity test we measured the contrast threshold for the identification of band-pass filtered letters. Before testing, comprehensive eye examination was carried out to reveal any structural or functional abnormality and to ensure correct refraction. The patients had healthy eyes, 2 out of 14 had reduced contrast sensitivity (Vistech) and 5 out of 14 had deficits in colour vision (FM 100). In both visual search tasks, the patients were statistically highly significantly (p<0.001) slower than the age-matched control observers. Instead, in the contrast sensitivity test, the difference between the patient and the control group was small relative to normal variability although still statistically significant (p<0.05). The results suggest that visual search tests can be useful in evaluating and characterising the effects of long-term solvent exposure on visual perception. Because our patients' letter contrast sensitivity was only moderately deteriorated, it seems that the observed defect of visual search cannot be explained by deteriorated letter identification alone, although it can be a contributory factor. Rather, the finding suggests that the speed by which visual information is transmitted and/or processed in the central visual system has become considerably slower.

Impairments of Colour Vision Induced by Organic Solvents: A Meta-Analysis Study

The impairment of colour discrimination induced by occupational exposure to toluene, styrene and mixtures of organic solvents is reviewed and analysed using a meta-analytical approach. Thirty-nine studies were surveyed covering a wide range of exposure conditions. Those studies using the Lanthony Panel D-15 desaturated test (D-15d) were further considered. From these for 15 samples data on colour discrimination ability (Colour Confusion Index, CCI) and exposure levels were provided, required for the meta-analysis. In accordance with previously reported higher CCI values for the exposed groups, the computations yielded positive effect sizes for 13 of the 15 samples, indicating that in the great majority of the studies the exposed groups showed inferior colour discrimination. However, the meta-analysis showed great variation in effect sizes across the studies. Possible reasons for inconsistency among the reported findings are discussed. These pertain to exposure-related parameters, as well as to confounders such as conditions of test administration and characteristics of subject samples. Those factors vary considerably among the studies and might have greatly contributed to divergence in measured colour vision capacity, thereby obscuring consistent effects of organic solvents on colour discrimination.

Colour vision and occupational toluene exposure: results of repeated examinations

Potential effects of human occupational exposures to toluene on colour vision were investigated in a follow-up study over 4 years with three repeated examinations. Colour vision was measured with the Lanthony desaturated colour vision test D-15d, and the colour confusion index (CCI) was calculated. The mean current exposures were 26+/-21 ppm for printers (high toluene level) and 3+/-4 ppm for end-processors (low toluene level). The mean exposure durations were 23+/-6 years for "long-time exposed" and 7+/-2 years for "short-time exposed" subjects. Repeated analyses (n=162) and multiple regressions (maximum available n=267) did not reveal significant effects of toluene with respect to intensity or duration of current or long-term exposure. Age and occupational qualification were significantly associated with CCI in both kinds of analysis, whereas alcohol consumption (carbohydrate-deficient transferrin, CDT) and smoking habits (cigarettes per day) were not. It is concluded that current industrial exposure limits of toluene provide sufficient protection against possible disturbance of colour vision.

Color vision impairment in workers exposed to neurotoxic chemicals

Recent research shows that occupational exposure to several solvents, metals and other industrial chemicals can impair color vision in exposed workers. Occupation-related color vision impairment usually results in blue-yellow color discrimination loss or, less frequently, a combination of blue-yellow and red-green loss. The eyes may be unequally involved, and the course is variable depending on exposure and other factors. The pathogenesis of occupational color vision loss has not been elucidated; it may be due to, e.g. a direct action of neurotoxins on receptors, possibly on the cone's membrane metabolism, and/or to an interference with neurotransmitters within the retina. Other possible pathogenetic mechanisms, such as a direct effect to the optic nerve, have also been suggested. Occupational color vision loss is usually sub-clinical, and workers are unaware of any deficit. It can be assessed using sensitive tests, such as the Farnsworth-Munsell 100 Hue (FM-100) or the Lanthony D-15 desaturated panel (D-15 d). The latter is the most widely used for studies in groups of exposed workers, and offers the possibility of a quantitative evaluation of the results by calculation of the Bowman's Color Confusion Index (CCI), or of the Vingrys' and King Smith's Confusion Index (CI). Other advantages of D-15 d are the possibility to perform the test directly at the workplace, and the reproducibility when performed in standardized conditions. In most cases, occupation-related color vision impairment is correlated to exposure levels, and has often been observed in workers exposed to environmental concentrations below the current occupational limit proposed by the ACGIH. Progression with increasing cumulative exposure has been reported, while reversibility is still discussed. Acquired color vision impairment related to occupational exposure to styrene, perchloroethylene (PCE), toluene, carbon disulfide, n-hexane, solvent mixtures, mercury and some other chemicals are discussed. Results show that color vision testing should be included in the evaluation of early neurotoxicity of chemicals in exposed workers. The D-15 d would be useful in the surveillance of workers exposed to solvents and other chemicals toxic to the visual system.

Occupational exposure to chemicals and sensory organs: a neglected research field

The effect of industrial chemicals on the sensory perception of exposed workers has received scant attention from the medical community to date, and the scientific literature is mainly limited to some case-reports or isolated studies. Possible explanations for this include the complexity of sensory perception, and the lack of agreement among researchers on methods for testing large groups of subjects. Nevertheless, some published studies showed that vision, hearing and olfactory function can be affected by various industrial metals and solvents, and some data exist also for touch and taste. This review discusses the main industrial chemicals involved. The pathogenesis of the toxicity of chemicals to sensory perception may be related to an action on receptors, nerve fibers, and/or the brain; probably, different pathogenetic mechanisms are involved. One of the main problems in this research field is that most of the studies to date evaluated the effect of a single industrial chemical on a single sense: as an example, we know that styrene exposure can impair smell and also hearing and vision but we have little idea whether different senses are impaired in the same worker, or whether each impairment is independent. In addition, workers are frequently exposed to different chemicals: co-exposure may have no effect, or result in both an increase or a decrease of the effect, as was observed for hearing loss, but studies on this aspect are largely insufficient. Research shows that both occupational and environmental exposure to industrial chemicals can affect sense organs, and suggests that the decline of perception with age may be, at least partly, related to this exposure. Nevertheless, available evidence is incomplete, and is largely inadequate for an estimation of a "safe" threshold of exposure. Good quality further research in this field is needed. This is certainly complex and demands adequate resources, but is justified by the ultimate result: the possibility to prevent an avoidable part of the decline in sensory function with age.