Characterizing the Visual Cortex Function in Cognitive Task-Induced Mental Load: An Functional Magnetic Resonance Imaging Study.

Introduction: The mental load caused by simultaneous multitasking can affect visual information processing and reduce its ability. This study investigated the effect of mental load caused by cognitive tasks simultaneously with visual task on the number of active voxels in the visual cortex. Methods: This study recruited 22 individuals with a mean age of 24.72 ± 5.47 years. 3-Tesla functional magnetic resonance imaging (fMRI) was used to examine the functions of the visual cortex and amygdala region during three different task conditions: visual task alone, visual task with an auditory n-back task, and visual task with an arithmetic task. The visual stimuli consisted of Gabor patches with a contrast of 55% at spatial frequencies of 0.25, 4, and 9 cycles per degree (cpd). These were presented in three trials of eight blocks with a stimulation time of 12 sec and a rest time of 14 sec. Results: Activated brain voxels in the primary, secondary, and associated visual cortex areas were reduced in response to the mental load imposed by the n-back and arithmetic tasks. This reduction was greater for a spatial frequency of 0.25 cpd in the n-back task condition and spatial frequency of 9 cpd in the arithmetic task condition. In addition, the amygdala was stimulated in 2-back task and arithmetic task conditions. Conclusions: This study revealed a decline in the number of activated voxels of the visual cortex due to the mental load caused by simultaneous cognitive tasks, confirming the findings of previous psychophysical studies.

Effect of Cognitive Mental Load on Attended and Nonattended Visual Stimuli.

SIGNIFICANCE: In the real word, visual tasks may be concurrent with other activity that imposes mental load. Although the brain's capacity to process information is limited, attention can improve visual performance by selectively allocating processing resources. Therefore, measuring visual performance under such circumstances can reflect patients' vision more accurately. PURPOSE: The aim of this study was to evaluate the effect of nonvisual task-induced mental load on visual performance at both attended and unattended locations in stimulus-driven captured attention. METHODS: Visual function was measured with an orientation discrimination task for Gabor patches with contrasts of 10, 15, 30, 50, and 80%. Three attentional conditions (valid-cue, invalid-cue, and neutral-cue) were randomly interleaved within runs. To modulate mental load, the visual task was performed either with or without a simultaneous auditory n-back task (two-back for maximum mental load and zero-back to control for the effect of having to perform a simultaneous task). RESULTS: Our result showed that the effect of mental load on correct responses was significant ( P = .02). Correct responses decreased significantly during the two-back task when compared with the baseline condition ( P = .03), but there was no significant difference between baseline and zero-back conditions ( P = .06). The effect of attention and spatial frequencies on the percentage of correct responses was significant ( P < .001). There was no significant interaction between mental load and spatial frequency, contrast level, or attention ( P > .05). CONCLUSIONS: Mental load had a similar decreasing effect on attended and unattended visual stimuli. This may be due to a generalized effect on processing resources upstream to where spatial attention is allocated.

Post-saccadic Eye Movement Indices Under Cognitive Load: A Path Analysis to Determine Visual Performance.

Purpose: The evidence on the linear relationship between cognitive load, saccade, fixation, and task performance was uncertain. We tested pathway models for degraded task performance resulting from changes in saccadic and post-saccadic fixation under cognitive load. Methods: Participants' (n = 38) eye movements were recorded using a post-saccadic discrimination task with and without arithmetic operations to impose cognitive load, validated through recording heart rate variability and subjective measurement. Results: Results showed that cognitive load led to longer latencies of saccade and fixation; more inaccurate responses and fewer secondary saccades (P < 0.001). Longer saccade latencies influenced task performance indirectly via increases in fixation latency, therefore, longer reaction times and higher response errors were observed due to limited fixation duration on desired target. Conclusion: We suggest that latency and duration of fixation indicate efficiency of information processing and can predict the speed and accuracy of task performance under cognitive load.

Long-term effects of methamphetamine abuse on visual evoked potentials.

PURPOSE: To compare visual evoked potential (VEP) components in normal individuals and those with long-term methamphetamine and crystal methamphetamine use. METHODS: In this study, monocular pattern-reversal VEPs were recorded in 40 methamphetamine and crystal methamphetamine users and 38 normal individuals. Visual stimuli were high-contrast (99%) checkerboard patterns at 15 and 60 min of arc with a reversal rate of 1.53 reversals per second. RESULTS: A significant difference was seen between the two groups for the P100 peak time for the 60 min of arc checks (p = 0.002, d = 0.75, 4.61% higher peak time in the addicted group) and the 15 min of arc checks (p = 0.004, d = 0.73, 4.78% higher peak time in the addicted group). However, other VEP components were not significantly different between the two groups. CONCLUSIONS: The higher P100 peak time at both 15 and 60 min of arc in methamphetamine-dependent users reveals that VEPs are highly sensitive for the diagnosis of retinal and visual pathway lesions.

The effect of mental load on psychophysical and visual evoked potential visual acuity.

PURPOSE: Under real-world conditions, tasks dependent on visual acuity may need to be performed in the presence of a mental load arising from concurrent, non-visual tasks. Therefore, measuring visual acuity concurrently with mentally demanding tasks may reflect a patient's vision more accurately. This study was designed to evaluate the impact of task-induced mental load on high contrast visual acuity, as measured using a letter chart and estimated via sweep visual evoked potentials (sweep VEP). METHODS: Visual acuity was determined using the Freiburg Vision Test, and also using sweep VEP tested stepwise, from coarse to fine, over 13 spatial frequencies, in 31 healthy participants (aged 22.4 ± 3.6 years). Recordings were repeated while participants concurrently performed an auditory 2-back task. Mental load of the n-back task was confirmed through subjective ratings. RESULTS: Visual acuity determined with the Freiburg Vision Test worsened from -0.02 ± 0.12 to 0.04 ± 0.15 logMAR under mental load (p = 0.03). Visual acuities estimated by sweep VEPs worsened from 0.38 ± 0.1 to 0.47 ± 0.1 logMAR (p < 0.001). While the slope of the VEP amplitude versus spatial frequency function steepened significantly with mental load (p = 0.01), VEP noise levels were not significantly affected (p = 0.07). CONCLUSION: Visual acuity reduces significantly with a concurrent task that produces mental load. At least part of this reduction appears to be related to alterations in responses within the visual cortex, rather than being purely attributable to higher-level distraction effects.

Macula and optic disk features in methamphetamine and crystal methamphetamine addicts using optical coherence tomography.

PURPOSE: Methamphetamine and crystal methamphetamine abusers were compared with healthy subjects using optical coherence tomography to assess their retinal nerve fiber layer, macula, and optic disk characteristics. METHODS: Forty-one methamphetamine and crystal methamphetamine abusers and 42 healthy subjects (mean ± SD of age: 35.82 ± 8.6 and 37.76 ± 9.1 years, respectively) were incorporated in this cross-sectional study. The drug abusers had a history of at least five years of substance use through smoking. Fourier-domain optical coherence tomography was used to image and assess the characteristics of retinal nerve fiber layer, macular thickness, and optic disk in the study groups. RESULTS: The retinal nerve fiber layer thickness was significantly lower in the superior and temporal retinal quadrants of drug abusers than healthy subjects (P = 0.008 and P = 0.028, respectively). This study did not find a significant difference between drug abusers and healthy controls regarding optic to disk ratio, rim area, and disk area (P > 0.05). The comparison between the study groups showed that the reductions in perifovea and the superior quadrant of parafoveal thickness were statistically significant (P < 0.001 and P = 0.029, respectively). CONCLUSION: Fourier-domain optical coherence tomography measurements showed that the retinal nerve fiber layer and macular thickness were different between methamphetamine and crystal methamphetamine abusers and healthy subjects, which should be considered in clinical practice. It seems that these drug abuses can cause alterations in retinal morphology.

Changes in corneal and anterior chamber indices due to methamphetamine abuse.

CLINICAL RELEVANCE: Considering the significant relationship between methamphetamine abuse and some anterior segment indices, methamphetamine abuse should be considered in differential diagnosis especially in the case of angle closure glaucoma. BACKGROUND: To investigate the effect of inhaled methamphetamine (meth) and crystal methamphetamine (crystal meth) on the quantitative indices of the cornea and anterior chamber using pentacam and anterior segment optical coherence tomography. METHODS: In this cross-sectional study, the participants were (crystal) meth addicts living in Zahedan. The participants were transported to the examination site to undergo imaging and optometric tests. Pentacam and anterior segment optical coherence tomography imaging were then conducted so as to evaluate corneal and anterior chamber quantitative indices. RESULTS: A total of 42 (crystal) meth addicts and 42 healthy subjects with matching age and gender were examined. Out of 42 subjects in the case group, 6 were female and 36 were male (mean age: 35.7 ± 8.6 years). The mean dose of drug used was 0.0074 ± 0.0034 g, and the mean duration of drug use was 6.9 ± 2.6 years (5-12 years). Based on the images of both devices, corneal curvature was significantly steeper in both meridians of anterior and posterior surfaces compared to the control group (p = 0.01). Among the anterior chamber parameters, the anterior chamber depth and volume were lower in the cases than the controls (p < 0.01). However, the lens rise was higher in addicts than controls (p = 0.01). CONCLUSION: Quantitative changes in corneal and anterior segment indices including dilated pupils, shallower anterior chamber depth and higher lens rise in addicted cases compared to the control group may precipitate the risk of closed-angle in these individuals.

Effect of Contact Lenses on Contrast Sensitivity under Various Lighting Conditions.

PURPOSE: To assess contrast sensitivity in clear and colored soft contact lenses under different lighting conditions. METHODS: This study was performed on 34 medical students. Visual acuity was measured using a tumbling E chart at a distance of 6 m, and contrast sensitivity was determined by Pelli Robson chart at a distance of 1 m. These tests were repeated in mesopic (3 lux) and glare (2000 lux) conditions. Then, a clear contact lens was applied to one eye and a colored contact lens was applied to the other. After 2 hr, visual acuity and contrast sensitivity were measured for each individual. The results were compared with and without contact lenses under normal, mesopic, and glare conditions. RESULTS: The mean refractive error was 0.44 ± 0.20 diopters. Repeated measures ANOVA showed a decline in contrast sensitivity with colored and clear contact lenses as compared to no-lens condition (P < 0.001). Additionally, lighting conditions had a significant impact on contrast sensitivity (P < 0.001); contrast sensitivity was lower in mesopic and glare conditions than under normal lighting condition. CONCLUSION: In addition to the drop in contrast sensitivity under unusual lighting conditions (e.g., glare and mesopic), wearing soft contact lenses can further reduce contrast sensitivity in different lighting conditions. Therefore, people who wear contact lenses should be aware of this reduction in visual performance in conditions like driving at night or in the fog.

Initial Power of Rigid Gas Permeable Contact Lenses in Patients with Keratoconus.

PURPOSE: To simplify the fitting process, this study was designed to predict the initial power of contact lenses using the regression model based on manual Javal keratometry data and refractive errors. METHODS: In this retrospective study, 121 eyes of 69 patients with keratoconus (KCN) were fitted with a specific trial set of rigid gas permeable contact lenses based on the standard criterion of "three-point touch" over a 7-year period. Power of the cornea was measured using Javal keratometer. Refractive errors and over refraction of patients were diagnosed using Topcon autorefractometer (RM-A2000) and confirmed by Heine beta 2000 retinoscope. RESULTS: The results of multiple linear regression showed the following equation: power of contact lens = -14.368 (constant of the final multiple regression model), +0.475 (spherical refraction), and +0.275 (flatter corneal power). CONCLUSIONS: The results of this study revealed that lens power has a significant relationship with the power of the flat corneal meridian and spherical refractive error in KCN patients. The obtained regression model can be used to shorten patients' chair time and optometric examination for predicting the power of contact lens.

Ocular abnormalities in beta thalassemia patients: prevalence, impact, and management strategies.

BACKGROUND: Beta thalassemia (ß-thalassemia) is a hereditary disease caused by defective globin synthesis and can be classified into three categories of minor (ß-TMi), intermedia (ß-TI), and major (ß-TM) thalassemia. The aim of our study is to investigate the effects of ß-thalassemia and its treatment methods on different parts of the eye and how early-diagnostic methods of ocular complications in this disorder would prevent further ocular complications in these patients by immediate treatment and diet change. METHODS: We developed a search strategy using a combination of the words Beta thalassemia, Ocular abnormalities, Iron overload, chelation therapy to identify all articles from PubMed, Web of Science, Scopus, and Google Scholar up to December 2018. To find more articles and to ensure that databases were thoroughly searched, the reference lists of selected articles were also reviewed. RESULTS: Complications such as retinopathy, crystalline lens opacification, color vision deficiency, nyctalopia, depressed visual field, reduced visual acuity, reduced contrast sensitivity, amplitude reduction in a-wave and b-wave in Electroretinography (ERG), and decrease in the Arden ratio in Electrooculography (EOG) have all been reported in ß-thalassemia patients undergoing chelation therapy. CONCLUSION: Ocular problems due to ß-thalassemia may be a result of anemia, iron overload in the body tissue, side effects of iron chelators, and the complications of orbital bone marrow expansion.

Contrast discrimination under task-induced mental load.

Task-induced mental load can potentially degrade visual performance, which could be important during tasks such as driving. In the natural world, most objects have visual contrasts that are supra-threshold, and so the ability to reliably distinguish the borders between these objects is related to contrast discrimination, rather than absolute contrast detection performance. This study investigated the effects of auditory task-induced mental load on contrast discrimination threshold across several spatial frequencies. Binocular contrast discrimination thresholds were measured in 14 participants at spatial frequencies of 0.25, 1, 4, 8, 14 cpd across pedestal contrast levels of 10, 16, 24, 38 and 60%. The task was repeated with an auditory 0-back task and 2-back task to impose a mental load, the magnitude of which was measured through subjective ratings and heart rate recording. A concurrent 2-back task significantly increased contrast discrimination thresholds across all spatial frequencies when compared to both the baseline and 0-back conditions. There was no significant effect of mental load on the slope of the Threshold vs Contrast function once potential ceiling effects in our staircase procedure were removed. We conclude that mental load induced by concurrent cognitive tasks can increase contrast discrimination thresholds. When evaluating an individuals' performance under natural-world condition such as driving, the effects of task-induced mental load on contrast discrimination thresholds should be considered.

Normative values of visual evoked potentials in Northeastern of Iran / Valores normativos de los potenciales evocados visuales en el Nordeste de Irán

Purpose: Visual evoked potentials (VEPs) provide important diagnostic information related to the functional integrity of the visual pathways. The aim of this study was to establish normative values of different components of pattern reversal VEPs on Iranian normal adult subjects. Methods: Monocular and binocular pattern reversal VEPs were recorded on 59 healthy participants (22.55 ± 3.79 years old) using the Roland RETI system for two check sizes of 15 and 60 min of arc. The measured VEP components were the latencies of N75, P100, N135 and amplitude of N75-P100. Results: Repeated measures ANOVA showed that viewing eye condition has a significant impact on the amplitude of N75-P100 (P < 0.001, F = 13.89). Also, the effect of check size on the latencies of N75, P100, N135, amplitude of N75-P100 (P ≤ 0.010), as well as the intraocular difference of P100 latency and amplitude N75-P100 (P = 0.007) was significant. More specifically, the amplitude of N75-P100 in both check sizes significantly differed between gender groups (P < 0.023). Conclusion: According to the results of this study, VEPs components are affected by the stimulus size, monocular and binocular recording conditions and gender. Therefore, it is necessary to determine the normative values of VEPs in each population, so that the results could be used in clinical studies

Objetivo: Los potenciales evocados visuales (PEV) aportan información diagnóstica importante relacionada con la integridad funcional de las vías visuales. El objetivo de este estudio fue establecer los valores normativos de los diferentes componentes de la reversión del patrón de PEV en adultos normales iraníes. Métodos: Se registraron los valores de reversión monocular y binocular del patrón de PEV en 59 participantes sanos (22,55 ± 3,79 años), utilizando el sistema Roland RETI para dos tamaños de comprobación de 15 y 60 min de arco. Los componentes medidos de PEV fueron las latencias de N75, P100, N135 y la amplitud de N75-P100. Resultados: La repetición de las medidas ANOVA reflejó que la situación del ojo de visión tiene un impacto significativo sobre la amplitud de N75-P100 (P < 0,001, F = 13,89). De igual modo, el efecto del tamaño de la comprobación de las latencias de N75, P100, N 135, la amplitud de N75-P100 (P ≤ 0,010), así como la diferencia intraocular de la latencia de P100 y la amplitud de N75-P100 (P = 0,007) fue significativo. Más específicamente, la amplitud de N75-P100 en ambos tamaños de comprobación difirió considerablemente entre los grupos de sexos (P < 0,023). Conclusión: Con arreglo a los resultados de este estudio, los componentes de los PEV se ven afectados por el tamaño del estímulo, las situaciones del registro monocular y binocular, y el sexo. Por tanto, es necesario determinar los valores normativos de los PEV en cada población, para poder utilizar los resultados en estudios clínicos

Normative values of visual evoked potentials in Northeastern of Iran.

PURPOSE: Visual evoked potentials (VEPs) provide important diagnostic information related to the functional integrity of the visual pathways. The aim of this study was to establish normative values of different components of pattern reversal VEPs on Iranian normal adult subjects. METHODS: Monocular and binocular pattern reversal VEPs were recorded on 59 healthy participants (22.55±3.79 years old) using the Roland RETI system for two check sizes of 15 and 60min of arc. The measured VEP components were the latencies of N75, P100, N135 and amplitude of N75-P100. RESULTS: Repeated measures ANOVA showed that viewing eye condition has a significant impact on the amplitude of N75-P100 (P<0.001, F=13.89). Also, the effect of check size on the latencies of N75, P100, N135, amplitude of N75-P100 (P≤0.010), as well as the intraocular difference of P100 latency and amplitude N75-P100 (P=0.007) was significant. More specifically, the amplitude of N75-P100 in both check sizes significantly differed between gender groups (P<0.023). CONCLUSION: According to the results of this study, VEPs components are affected by the stimulus size, monocular and binocular recording conditions and gender. Therefore, it is necessary to determine the normative values of VEPs in each population, so that the results could be used in clinical studies.

Prevalence of color vision deficiency among arc welders / Prevalencia de la deficiencia de la visión del color entre los soldadores con arco eléctrico

Purpose: This study was performed to investigate whether occupationally related color vision deficiency can occur from welding. Methods: A total of 50 male welders, who had been working as welders for at least 4 years, were randomly selected as case group, and 50 age matched non-welder men, who lived in the same area, were regarded as control group. Color vision was assessed using the Lanthony desatured panel D-15 test. The test was performed under the daylight fluorescent lamp with a spectral distribution of energy with a color temperature of 6500K and a color rendering index of 94 that provided 1000lx on the work plane. The test was carried out monocularly and no time limit was imposed. All data analysis were performed using SPSS, version 22. Results: The prevalence of dyschromatopsia among welders was 15% which was statistically higher than that of nonwelder group (2%) (p=0.001). Among welders with dyschromatopsia, color vision deficiency in 72.7% of cases was monocular. There was positive relationship between the employment length and color vision loss (p=0.04). Similarly, a significant correlation was found between the prevalence of color vision deficiency and average working hours of welding a day (p=0.025). Conclusions: Chronic exposure to welding light may cause color vision deficiency. The damage depends on the exposure duration and the length of their employment as welders (AU)

Objetivo: Este estudio se realizó para investigar si se puede producir una deficiencia de la visión del color relacionada con la profesión de soldador. Métodos: Se seleccionó como grupo del caso a un total de 50 soldadores que habían ejercido la profesión durante un mínimo de cuatro años, y se les comparó con 50 varones no soldadores que vivían en la misma zona, como grupo de control. Se evaluó la visión del color utilizando el test Lanthony D-15 desaturado. La prueba se llevó a cabo bajo la lámpara fluorescente de luz de día, con una distribución energética espectral con temperatura cromática de 6.500K y un índice de representación de 94 que aportaba 1000 lux en el plano de trabajo. La prueba se realizó de forma monocular, no imponiéndose ningún límite de tiempo. Los análisis de los datos se realizaron utilizando el software SPSS, versión 22. Resultados: La prevalencia de la discromatopsia entre los soldadores fue del 15%, lo cual fue estadísticamente superior al grupo de no soldadores (2%) (p=0,001). Entre los soldadores con discromatopsia, la deficiencia de la visión del color en el 72,7% de los casos fue monocular. Se produjo una relación positiva entre la duración del empleo y la pérdida de la visión del color (p=0,04). De forma similar, hallamos una correlación entre la prevalencia de la deficiencia de la visión del color y la media de horas laborales de una jornada de soldadura (p=0,025). Conclusiones: La exposición crónica a la luz de la soldadura puede causar una deficiencia de la visión del color. El daño depende de la duración de la exposición, y del tiempo en la profesión como soldadores (AU)

Prevalence of color vision deficiency among arc welders.

PURPOSE: This study was performed to investigate whether occupationally related color vision deficiency can occur from welding. METHODS: A total of 50 male welders, who had been working as welders for at least 4 years, were randomly selected as case group, and 50 age matched non-welder men, who lived in the same area, were regarded as control group. Color vision was assessed using the Lanthony desatured panel D-15 test. The test was performed under the daylight fluorescent lamp with a spectral distribution of energy with a color temperature of 6500K and a color rendering index of 94 that provided 1000lx on the work plane. The test was carried out monocularly and no time limit was imposed. All data analysis were performed using SPSS, version 22. RESULTS: The prevalence of dyschromatopsia among welders was 15% which was statistically higher than that of nonwelder group (2%) (p=0.001). Among welders with dyschromatopsia, color vision deficiency in 72.7% of cases was monocular. There was positive relationship between the employment length and color vision loss (p=0.04). Similarly, a significant correlation was found between the prevalence of color vision deficiency and average working hours of welding a day (p=0.025). CONCLUSIONS: Chronic exposure to welding light may cause color vision deficiency. The damage depends on the exposure duration and the length of their employment as welders.

Effect of yellow filter on visual acuity and contrast sensitivity under glare condition among different age groups.

The aim of this study is to investigate the effect of yellow filter on visual acuity and contrast sensitivity under glare condition for various ages. A total of 60 subjects, aged 5-60 years, with no ocular pathology and no previous surgery were assessed in this cross-sectional study. We divided subjects into six subgroups according to their ages, and the number of subjects in each group was 10: group 1, aged 5-10 years; group 2, aged 11-20 years; group 3, aged 21-30 years; group 4, aged 31-40 years; group 5, aged 41-50 years; and group 6, aged 51-60 years. Snellen visual acuity and Pelli Robson contrast sensitivity with and without glare and with the use of yellow filter under glare condition were determined. Data analysis was carried out using SPSS, version 20. Our results showed a significant reduction in contrast sensitivity under glare condition in all age groups (p = 0.000), which improved significantly with the use of yellow filter (p = 0.000). Although when data in different age groups were analyzed separately, this improvement was only significant in older subjects, aged 51-60 years (p = 0.007). No significant difference was found between Snellen visual acuity with and without glare (p = 0.083), and also we found no yellow filter effect on visual acuity under glare condition. We conclude that yellow filter, which absorbs short wavelength, may provide significant contrast sensitivity benefits for individuals and influences older subjects more than younger ones.

The Effect of Holy Quran Voice on Mental Health.

This study was designed to determine the effect of Quran listening without its musical tone (Tartil) on the mental health of personnel in Zahedan University of Medical Sciences, southeast of Iran. The results showed significant differences between the test and control groups in their mean mental health scores after Quran listening (P = 0.037). No significant gender differences in the test group before and after intervention were found (P = 0.806). These results suggest that Quran listening could be recommended by psychologists for improving mental health and achieving greater calm.