Navegando por Autor "GOMES, Bruno Duarte"
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Item Acesso aberto (Open Access) 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 LimaThe 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.Item Acesso aberto (Open Access) Comparative neurophysiology of spatial luminance contrast sensitivity(2011-06) SOUZA, Givago da Silva; GOMES, Bruno Duarte; SILVEIRA, Luiz Carlos de LimaThe luminance contrast sensitivity function has been investigated using behavioral and electrophysiological methods in many vertebrate species. Some features are conserved across species as a shape of the function, but other features, such as the contrast sensitivity peak value, spatial frequency contrast sensitivity peak, and visual acuity have changed. Here, we review contrast sensitivity across different classes of vertebrates, with an emphasis on the frequency contrast sensitivity peak and visual acuity. We also correlate the data obtained from the literature to test the power of the association between visual acuity and the spatial frequency of the contrast sensitivity function peak.Item Acesso aberto (Open Access) Comparison of the reliability of multifocal visual evoked cortical potentials generated by pattern reversal and pattern pulse stimulation(2012-10) SOUZA, Givago da Silva; SCHAKELFORD, H.B.; MOURA, Ana Laura de Araújo; GOMES, Bruno Duarte; VENTURA, Dora Selma Fix; FITZGERALD, M.E.C.; SILVEIRA, Luiz Carlos de LimaThis study compared the effectiveness of the multifocal visual evoked cortical potentials (mfVEP) elicited by pattern pulse stimulation with that of pattern reversal in producing reliable responses (signal-to-noise ratio >1.359). Participants were 14 healthy subjects. Visual stimulation was obtained using a 60-sector dartboard display consisting of 6 concentric rings presented in either pulse or reversal mode. Each sector, consisting of 16 checks at 99% Michelson contrast and 80 cd/m2 mean luminance, was controlled by a binary m-sequence in the time domain. The signal-to-noise ratio was generally larger in the pattern reversal than in the pattern pulse mode. The number of reliable responses was similar in the central sectors for the two stimulation modes. At the periphery, pattern reversal showed a larger number of reliable responses. Pattern pulse stimuli performed similarly to pattern reversal stimuli to generate reliable waveforms in R1 and R2. The advantage of using both protocols to study mfVEP responses is their complementarity: in some patients, reliable waveforms in specific sectors may be obtained with only one of the two methods. The joint analysis of pattern reversal and pattern pulse stimuli increased the rate of reliability for central sectors by 7.14% in R1, 5.35% in R2, 4.76% in R3, 3.57% in R4, 2.97% in R5, and 1.78% in R6. From R1 to R4 the reliability to generate mfVEPs was above 70% when using both protocols. Thus, for a very high reliability and thorough examination of visual performance, it is recommended to use both stimulation protocols.Item Acesso aberto (Open Access) Contrast sensitivity of pattern transient VEP components: contribution from M and P pathways(2013-12) SOUZA, Givago da Silva; GOMES, Bruno Duarte; LACERDA, Eliza Maria da Costa Brito; SAITO, Cézar Akiyoshi; SILVA FILHO, Manoel da; SILVEIRA, Luiz Carlos de LimaThe purpose of this study was to compare contrast sensitivity estimated from transient visual evoked potentials (VEPs) elicited by achromatic pattern-reversal and pattern-onset/offset modes. The stimuli were 2-cpd, achromatic horizontal gratings presented either as a 1 Hz pattern reversal or a 300 ms onset/700 ms offset stimulus. Contrast thresholds were estimated by linear regression to amplitudes of VEP components vs. the logarithm of the stimulus contrasts, and these regressions were extrapolated to the zero amplitude level. Contrast sensitivity was defined as the inverse of contrast threshold. For pattern reversal, the relation between the P100 amplitude and log of the stimulus contrast was best described by two separate linear regressions. For the N135 component, a single straight line was sufficient. In the case of pattern onset/offset for both the C1 and C2 components, single straight lines described their amplitude vs. log contrast relations in the medium-to-low contrast range. Some saturation was observed for C2 components. The contrast sensitivity estimated from the low-contrast limb of the P100, from the N135, and from the C2 were all similar but higher than those obtained from the high-contrast limb of the P100 and C1 data, which were also similar to each other. With 2 cpd stimuli, a mechanism possibly driven by the M pathway appeared to contribute to the P100 component at medium-to-low contrasts and to the N135 and C2 components at all contrast levels, whereas another mechanism, possibly driven by the P and M pathways, appeared to contribute to the P100 component at high contrast and C1 component at all contrast levels.Item 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 LimaThe 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.Item Acesso aberto (Open Access) Métodos utilizados na avaliação psicofísica da visão de cores humana(2011) LIMA, Monica Gomes; GOMES, Bruno Duarte; VENTURA, Dora Selma Fix; SILVEIRA, Luiz Carlos de LimaColor is a perceptual attribute that allows organisms to identify and to locate environmental patterns of equal brightnesses and constitutes an additional dimension in object identification, in addition to the detection of several other object dimensions in relation with the visual scene. Color therefore serves an important role in animal and human interaction with the environment. By supplying ways to evaluate aspects of human vision, including color vision, visual psychophysics focusses on the quantitative study of the relation between physical events of sensory stimulation and the resulting behavioral response. The objective of this paper is to demonstrate several efficient techniques in the evaluation of the chromatic human vision through adaptive psychophysical methods.Item Acesso aberto (Open Access) Optical coherence tomography and multifocal electroretinography of patients with advanced neovascular age related macular degeneration before, during, and after treatment with ranibizumab(Universidade Federal do Pará, 2015-06-02) ALMEIDA, Izabela Negrão Frota de; ALMEIDA, Luciana Negrão Frota de; SOBRINHO, Edmundo Frota de Almeida; GOMES, Bruno Duarte; SOUZA, Givago da Silva; ROSA, Alexandre Antonio Marques; SILVEIRA, Luiz Carlos de LimaTo evaluate retinal morphology and function of patients with advanced neovascular age-related macular degeneration (AMD) before, during, and after treatment with ranibizumab. Methods: Twenty-one eyes diagnosed with advanced AMD were studied with optical coherence tomography (OCT) and multifocal electroretinography (mfERG). Three intravitreal injections of ranibizumab were administered at 1-month intervals. Evaluations were performed before the first injection (D0) and at 30 (D30), 60 (D60), and 90 days (D90) after the first injection and compared to an age-matched control group (n=21 eyes). Results: The thickness of macular retinal layers increased before treatment due to the presence of intraretinal fluid. A thick retinal pigment epithelium-choriocapillaris complex (RPE-CC) suggested the presence of choroidal neovascular membrane. Intraretinal edema decreased after treatment (P<0.01), but persisting RPE-CC thickness resulted in a subretinal scar. Three different annular retinal areas were studied with mfERG (from center to periphery: rings R1, R2, and R3). The amplitude of the first negative component (N1) decreased in R1, R2, and R3 at D30, D60, and D90 when compared with that in controls (P<0.05); the N1 implicit time was delayed in R3 at D30 (P<0.05). The amplitude of the first positive component (P1) was reduced in R1 and R2 at D30, D60, and D90 when compared with that in controls (P<0.01); the P1 implicit time was delayed in R1 at D0 and D60 (P<0.05), in R2 at D0, D30, and D90 (P<0.01), and in R3 at D30 and D60 (P<0.05). Conclusion: Ranibizumab reduces intraretinal edema, even in advanced cases. Central macular activity appeared to increase after the initiation of treatment, improving over time.