Luminance contrast sensitivity and colour vision are considered to have great predictive value in the evaluation of type 2 diabetic retinopathy. However, these two visual characteristics have seldom been investigated in the same group of patients. In the present study we measured contrast sensitivity and colour vision in a group of patients with type 2 diabetes and correlated the results with estimates of common metabolic markers for the disease. A subgroup of the patients had no clinical signs of retinopathy.
We used psychometric functions to estimate the joint entropy for space discrimination and spatial frequency discrimination. Space discrimination was taken as discrimination of spatial extent. Seven subjects were tested. Gábor functions comprising unidimensionalsinusoidal gratings (0.4, 2, and 10 cpd) and bidimensionalGaussian envelopes (1°) were used as reference stimuli. The experiment comprised the comparison between reference and test stimulithat differed in grating's spatial frequency or envelope's standard deviation. We tested 21 different envelope's standard deviations around the reference standard deviation to study spatial extent discrimination and 19 different grating's spatial frequencies around the reference spatial frequency to study spatial frequency discrimination. Two series of psychometric functions were obtained for 2%, 5%, 10%, and 100% stimulus contrast. The psychometric function data points for spatial extent discrimination or spatial frequency discrimination were fitted with Gaussian functions using the least square method, and the spatial extent and spatial frequency entropies were estimated from the standard deviation of these Gaussian functions. Then, joint entropy was obtained by multiplying the square root of space extent entropy times the spatial frequency entropy. We compared our results to the theoretical minimum for unidimensional Gábor functions, 1/4? or 0.0796. At low and intermediate spatial frequencies and high contrasts, joint entropy reached levels below the theoretical minimum, suggesting non-linear interactions between two or more visual mechanisms. We concluded that non-linear interactions of visual pathways, such as the M and P pathways, could explain joint entropy values below the theoretical minimum at low and intermediate spatial frequencies and high contrasts. These non-linear interactions might be at work at intermediate and high contrasts at all spatial frequencies once there was a substantial decrease in joint entropy for these stimulus conditions when contrast was raised.
This study evaluated current levels of mercury exposure and sensory symptoms in adults from three riverine communities in Pará State, Brazil, two of which located in the Tapajós River basin and one in the Tocantins basin. Participants in this study included 78 residents in Barreiras (Tapajós), 30 in São Luiz do Tapajós (Tapajós), and 49 in Furo do Maracujá (Tocantins). Total hair mercury concentrations were quantified by atomic absorption spectrophotometry, and neurological evaluation was conducted by routine examination. Mercury concentrations in the Tapajós communities were higher than those in the Tocantins (p < 0.01). Evaluation of neurological changes showed no significant difference between the communities in exposed areas and control areas for the changes observed by conventional neurological examination, except for gait deviation (p < 0.05). The study concludes that despite the mercury exposure levels, there was a low frequency of sensory alterations according to conventional neurological testing.
The contributions of contrast detection mechanisms to the visual cortical evoked potential (VECP) have been investigated studying the contrast-response and spatial frequency-response functions. Previously, the use of m-sequences for stimulus control has been almost restricted to multifocal electrophysiology stimulation and, in some aspects, it substantially differs from conventional VECPs. Single stimulation with spatial contrast temporally controlled by m-sequences has not been extensively tested or compared to multifocal techniques. Our purpose was to evaluate the influence of spatial frequency and contrast of sinusoidal gratings on the VECP elicited by pseudo-random stimulation. Nine normal subjects were stimulated by achromatic sinusoidal gratings driven by pseudo random binary m-sequence at seven spatial frequencies (0.4-10 cpd) and three stimulus sizes (4°, 8°, and 16° of visual angle). At 8° subtence, six contrast levels were used (3.12-99%). The first order kernel (K1) did not provide a consistent measurable signal across spatial frequencies and contrasts that were tested-signal was very small or absent-while the second order kernel first (K2.1) and second (K2.2) slices exhibited reliable responses for the stimulus range. The main differences between results obtained with the K2.1 and K2.2 were in the contrast gain as measured in the amplitude versus contrast and amplitude versus spatial frequency functions. The results indicated that K2.1 was dominated by M-pathway, but for some stimulus condition some P-pathway contribution could be found, while the second slice reflected the P-pathway contribution. The present work extended previous findings of the visual pathways contribution to VECP elicited by pseudorandom stimulation for a wider range of spatial frequencies.
The objective of this study was to evaluate the visual loss due to dengue fever using retinal and cortical electrophysiology and retinal imaging. The participants were three female patients with low visual acuity after dengue fever. They were evaluated by routine ophthalmological investigations, transient pattern electroretinogram (tPERG), transient pattern visual evoked cortical potential (tPVECP), and retinal optical coherence tomography (retinal OCT). tPERG and tPVECP amplitude (microV) and implicit time (ms) were the parameters evaluated using OCT retinal thickness (microm) and reflectivity. All patients presented low visual acuity and scotomata with or without changes in the oculus fundus. tPERG from two patients showed decreased amplitude or absence of the main components; it was not possible to record a reliable response in the third patient due to excessive blinking. tPVECP at 0.5 cpd was normal in all three patients, while at 2 cpd the main components were absent in one patient and normal in the other two patients. OCT image was abnormal in two patients, one of them with high reflectance areas and another with decreased retinal thickness (the third patient was not studied with this technique).The dengue fever can lead to visual impairment detectable by ophthalmological exams such as angiography, retinography, and OCT imaging, as well as retinal and cortical electrophysiology. Dengue maculopathy which could be caused by vascular alterations and/or aberrant immune response after infection may result in temporary or permanent visual losses.
To evaluate the visual system of patients suffering from type I or VI mucopolysaccharidosis (MPS) by recording the visual evoked cortical potential (VECP).
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