Navegando por Autor "RODRIGUES, Anderson Raiol"

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Chromatic spatial contrast sensitivity estimated by visual evoked cortical potential and psychophysics
(2013-02) BARBONI, Mirella Telles Salgueiro; GOMES, Bruno Duarte; SOUZA, Givago da Silva; RODRIGUES, Anderson Raiol; VENTURA, Dora Selma Fix; SILVEIRA, Luiz Carlos de Lima
The purpose of the present study was to measure contrast sensitivity to equiluminant gratings using steady-state visual evoked cortical potential (ssVECP) and psychophysics. Six healthy volunteers were evaluated with ssVECPs and psychophysics. The visual stimuli were red-green or blue-yellow horizontal sinusoidal gratings, 5° × 5°, 34.3 cd/m2 mean luminance, presented at 6 Hz. Eight spatial frequencies from 0.2 to 8 cpd were used, each presented at 8 contrast levels. Contrast threshold was obtained by extrapolating second harmonic amplitude values to zero. Psychophysical contrast thresholds were measured using stimuli at 6 Hz and static presentation. Contrast sensitivity was calculated as the inverse function of the pooled cone contrast threshold. ssVECP and both psychophysical contrast sensitivity functions (CSFs) were low-pass functions for red-green gratings. For electrophysiology, the highest contrast sensitivity values were found at 0.4 cpd (1.95 ± 0.15). ssVECP CSF was similar to dynamic psychophysical CSF, while static CSF had higher values ranging from 0.4 to 6 cpd (P < 0.05, ANOVA). Blue-yellow chromatic functions showed no specific tuning shape; however, at high spatial frequencies the evoked potentials showed higher contrast sensitivity than the psychophysical methods (P < 0.05, ANOVA). Evoked potentials can be used reliably to evaluate chromatic red-green CSFs in agreement with psychophysical thresholds, mainly if the same temporal properties are applied to the stimulus. For blue-yellow CSF, correlation between electrophysiology and psychophysics was poor at high spatial frequency, possibly due to a greater effect of chromatic aberration on this kind of stimulus.
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Color vision loss in patients treated with chloroquine
(2003) VENTURA, Dora Selma Fix; SILVEIRA, Luiz Carlos de Lima; NISHI, Mauro; COSTA, Marcelo Fernandes da; GUALTIERI, Mirella; ALEXANDRE, Ruth Mayanna Araújo dos Santos; PINTO, Carolina Trindade; MOURA, Ana Laura de Araújo; RODRIGUES, Anderson Raiol; SAKURADA, Claudio; SAUMA, Maria de Fátima L. C.; SOUZA, John Manuel de
Patients that make use of chloroquine or hydroxychloroquine, drugs which are frequently administered for treatment of rheumatoid arthritis, lupus erithromatosus or malaria, may suffer alterations in color vision and in contrast sensitivity. The present work evaluates the visual function of these patients in a joint study of the University of São Paulo (USP), in São Paulo, and of the Federal University of Pará (UFPA), in Belém. Thirty two chloroquine user patients without alterations in the eye fundus exam were evaluated in São Paulo (n=10; aged 38 to 71 years; mean=55,8 years) and in Belém (n=22; aged 20 to 67; mean=40 years). The prescribed accumulated chloroquine dose was 45 to 430 g (mean=213 g; sd = 152 g) for the São Paulo group, and 36 to 540 g (mean=174 g; sd=183 g) for the Belém group. Tests were performed monocularly with corrected eye refractive state. Color discrimination was evaluated using the Cambridge Colour Test (CCT): the color discrimination threshold was measured first in the protan, deutan and tritan axes and, in succession, three MacAdam's ellipses were determined. The patient's color vision was also evaluated with color arrangement tests: the Farnsworth-Munsell 100 Hue (FM100), the Farnsworth-Munsell D15, and the Lanthony Desaturated (D15d) tests. We also measured the contrast sensitivity for black-and-white sine wave grating of twenty two patients. The results were compared with controls without ophthalmologic or neuro-ophthalmologic pathologies. Twenty four patients presented acquired dyschromatopsia. There were cases of selective loss (11 patients) and of diffuse loss (13 patients). Although losses were present in the FM100 there was no correlation between the FM100 error score and the ellipse area measured by the CCT. Moreover, three patients that scored normal in the FM100, failed to reach normal threshold in the CCT. The Lanthony test was less sensitive than the other two tests, since it failed to indicate loss in about half the patients, and the D15 was the least sensitive test, having failed to indicate loss in 9 out of 10 patients. Contrast sensitivity was within normal values for patients submitted to this test. The extent of losses in color discrimination was positively correlated with the accumulated dose. The CCT is recommended for follow up since it provides quantitative data that can be directly interpreted in CIE (Commission Internationalle d'Éclairage) color space.
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Comparative study of human exposure to mercury in riverside communities in the Amazon region
(2006-03) PINHEIRO, Maria da Conceição Nascimento; OIKAWA, Teiichi; VIEIRA, José Luiz Fernandes; GOMES, M S V; GUIMARÃES, Geraldo de Assis; CRESPO LÓPEZ, Maria Elena; MÜLLER, Regina Celi Sarkis; AMORAS, Walter Wanderley; RIBEIRO, Danielle Regina Gomes; RODRIGUES, Anderson Raiol; CÔRTES, Maria Izabel Tentes; SILVEIRA, Luiz Carlos de Lima
Four populations in the Amazon area were selected for a comparative study of mercury-exposed and non-exposed populations: São Luiz do Tapajós, Barreiras, Panacauera, and Pindobal Grande. The highest mercury levels in human hair samples were found in São Luiz do Tapajós and Barreiras, greatly exceeding the limits established by the World Health Organization. Panacauera showed an intermediate level below 9 µg/g. This was the first comparative and simultaneous evaluation of mercury exposure in the Amazon area. Also, thanks to this type of monitoring, we were able to eliminate the uncertainties about the reference dose. On the basis of these data, we can conclude that the mercury levels detected in exposed populations of the Tapajós River basin may be dangerous not only because they are above the World Health Organization limits, but also because the simultaneous mercury detection in non-exposed populations with similar characteristics provided a valid control and revealed lower mercury levels. Our results support the importance of continuous monitoring in both exposed and non-exposed populations.
Acesso aberto (Open Access)
Division of labor between M and P visual pathways: different visual pathways minimize joint entropy differently
(2008-06) SILVEIRA, Luiz Carlos de Lima; SAITO, Cézar Akiyoshi; MELLO JÚNIOR, Harold Dias de; SILVEIRA, Vladímir de Aquino; SOUZA, Givago da Silva; RODRIGUES, Anderson Raiol; SILVA FILHO, Manoel da
Visual perception and action are strongly linked with parallel processing channels connecting the retina, the lateral geniculate nucleus, and the input layers of the primary visual cortex. Achromatic vision is provided by at least two of such channels formed by the M and P neurons. These cell pathways are similarly organized in primates having different lifestyles, including species that are diurnal, nocturnal, and which exhibit a variety of color vision phenotypes. We describe the M and P cell properties by 3D Gábor functions and their 3D Fourier transform. The M and P cells occupy different loci in the Gábor information diagram or Fourier Space. This separation allows the M and P pathways to transmit visual signals with distinct 6D joint entropy for space, spatial frequency, time, and temporal frequency. By combining the M and P impacts on the cortical neurons beyond V1 input layers, the cortical pathways are able to process aspects of visual stimuli with a better precision than it would be possible using the M or P pathway alone. This performance fulfils the requirements of different behavioral tasks.
Acesso aberto (Open Access)
Estimativa da sensibilidade ao contraste espacial de luminância e discriminação de cores por meio do potencial provocado visual transiente
(2006) GOMES, Bruno Duarte; SOUZA, Givago da Silva; RODRIGUES, Anderson Raiol; SAITO, Cézar Akiyoshi; SILVA FILHO, Manoel da; SILVEIRA, Luiz Carlos de Lima
The Visual Evoked Potential (VEP) is a cortical response obtainable on the scalp. It usually reflects the activity from V1 neurons. It is classified in transient or steady-state, according with the temporal frequency of stimulation. Other stimuli properties evoke a selective activity from different neuronal groups found in V1. This way, VEP have been used to study luminance and chromatic human vision. Several studies used VEP to estimate luminance contrast sensitivity in the spatial frequency domain. More recently, some studies used VEP to measure color discrimination thresholds. The transient VEP shows a good agreement with psychophysical measurements of spatial luminance contrast sensitivity and color discrimination, being a noninvasive method to study vision from subjects with difficulty to perform psychophysical tests.
Acesso aberto (Open Access)
Impairment of color spatial vision in chronic alcoholism measured by psychophysical methods
(2009-12) CASTRO, Antonio José de Oliveira; RODRIGUES, Anderson Raiol; CÔRTES, Maria Izabel Tentes; SILVEIRA, Luiz Carlos de Lima
We used psychophysical tests to evaluate spatial vision in 15 subjects with a clinical history of chronic alcoholism by measuring luminance contrast sensitivity and color discrimination. The subjects were initially subjected to clinical inquiry and ophthalmological exam. Subjects then performed psychophysical tests to measure spatial contrast thresholds using sine wave gratings of different spatial frequencies and contrasts and chromatic discrimination thresholds using the Mollon-Reffin test. For the analysis, subjects were divided into three groups according to age and compared with age-matched controls. Ten subjects had some degree of color vision loss, which was quite severe in seven cases. All subjects had normal luminance contrast sensitivity. The results suggest that color vision changes related to chronic alcoholism can occur in the absence of impairment of spatial luminance contrast sensitivity and thus is an important aspect to be considered in the clinical evaluation of this condition.
Acesso aberto (Open Access)
Mercury toxicity in the Amazon: contrast sensitivity and color discrimination of subjects exposed to mercury
(2007-03) RODRIGUES, Anderson Raiol; SOUZA, Cleidson Ronald Botelho de; BRAGA, Alexandre Melo; RODRIGUES, Paulo Sergio Silva; SILVEIRA, Antonio Tobias; DAMIN, Enira Teresinha Braghirolli; CÔRTES, Maria Izabel Tentes; CASTRO, Antonio José de Oliveira; MELLO, Guilherme Arantes; VIEIRA, José Luiz Fernandes; PINHEIRO, Maria da Conceição Nascimento; VENTURA, Dora Selma Fix; SILVEIRA, Luiz Carlos de Lima
We measured visual performance in achromatic and chromatic spatial tasks of mercury-exposed subjects and compared the results with norms obtained from healthy individuals of similar age. Data were obtained for a group of 28 mercury-exposed subjects, comprising 20 Amazonian gold miners, 2 inhabitants of Amazonian riverside communities, and 6 laboratory technicians, who asked for medical care. Statistical norms were generated by testing healthy control subjects divided into three age groups. The performance of a substantial proportion of the mercury-exposed subjects was below the norms in all of these tasks. Eleven of 20 subjects (55%) performed below the norms in the achromatic contrast sensitivity task. The mercury-exposed subjects also had lower red-green contrast sensitivity deficits at all tested spatial frequencies (9/11 subjects; 81%). Three gold miners and 1 riverine (4/19 subjects, 21%) performed worse than normal subjects making more mistakes in the color arrangement test. Five of 10 subjects tested (50%), comprising 2 gold miners, 2 technicians, and 1 riverine, performed worse than normal in the color discrimination test, having areas of one or more MacAdam ellipse larger than normal subjects and high color discrimination thresholds at least in one color locus. These data indicate that psychophysical assessment can be used to quantify the degree of visual impairment of mercury-exposed subjects. They also suggest that some spatial tests such as the measurement of red-green chromatic contrast are sufficiently sensitive to detect visual dysfunction caused by mercury toxicity.