Visual Contrast Sensitivity Function Research Articles

Photoreceptor and vision protective effects of astragaloside IV in mice model with light-evoked retinal damage

Cone cell-enriched macular degeneration is a major cause of functional vision deterioration. Astragaloside IV (Asg IV), an active triterpenoid saponin component with properties of anti-oxidative and anti-apoptotic damage, which benefit retinal tissue and capillaries. But, the nutraceutical therapeutic effects on functional vision have not been fully evaluated. In this study, mice were administrated to high-intensity light exposure after either receiving a vehicle or Asg IV (0.05, 0.5, and 50 mg/kg, BID). During this time, their spatial-visual performance, visual acuity (VA), and visual contrast sensitivity function (VCSF) were measured using the behavioral optomotor reflex method. Morphological changes in the retina were determined by histological examination. High energy light-evoked visual damage was confirmed by the loss in structural tissue integrity in the retina accompanied by a decline in both VA and VCSF, whereas the retina tissue exhibited loss of cone cell density and severe cone-specific opsin misplacement. In contrast, prophylactic oral Asg IV (0.5, and 50 mg/kg, BID)-treated exerted protective and improvement effects against light-evoked deterioration of functional vision. Asg IV treatment significantly improved the thresholds of VA and VCSF. In particular, Asg IV (50 mg/kg, BID) modulated and increased the survival of the photoreceptors, especially the cone cells, which targeted and enhanced the high spatial frequency-characterized VCSF. In contrast, the cellular protective effect of Asg IV (50 mg/kg, BID) on photoreceptors was significantly reversed by synchronous injection of a glucocorticoid receptor (GR) antagonist (mifepristone). This study demonstrated the major neuroretina-protective effect and functional vision-improving effect of Asg IV in vivo.

The Functional Vision Restorative Effect of Crocin via the BDNF-TrkB Pathway: An In Vivo Study.

Abnormal dislocation of cone opsin protein affects the sensitivity function of photoreceptors and results in depressed central vision. Nutraceutical therapy is needed to restore the residual function of photoreceptors. Crocin is a natural substance for retinal health. However, its effect on the restoration of functional vision and its underlying mechanisms have not been fully studied. This study analyzed the restorative effect of crocin on residual functional vision in vivo in a mouse model. High-energy light-evoked photoreceptor dysfunction was confirmed by M opsin dislocation in the retina accompanied by a loss of functional vision. Crocin treatment significantly increased brain-derived neurotrophic factor (BDNF) protein in retinas, thus contributing to the re-localization of the M opsin protein, restoration of the visual acuity (VA), and high spatial frequency-characterized visual contrast sensitivity function (VCSF). In contrast, such effects were significantly reversed after the washout period. Additionally, the restorative effect of crocin on functional vision and M opsin re-localization can be reversed and blocked by synchronous injection of a tropomyosin receptor kinase B (TrkB) receptor antagonist (ANA-12). This study demonstrated the major functional vision-rescuing or restoring effect of crocin in vivo by modulating M opsin location plasticity and increasing the capacity of the residual photoreceptor function through the BDNF–TrkB receptor pathway.

Protective Effect of a Water-Soluble Carotenoid-Rich Extract of Cordyceps militaris against Light-Evoked Functional Vision Deterioration in Mice.

Light-evoked retinal photodamage is considered an important factor contributing to functional vision deterioration and can even lead to light maculopathy or dry age-related macular degeneration. Loss of visual acuity (VA) and visual contrast sensitivity function (VCSF) are the major symptoms of retinal degenerative diseases. Cordyceps militaris is a carotenoid-rich Chinese medicinal fungus with antioxidant, anti-inflammatory, and immunomodulatory functions. C. militaris extract is a natural substance, and its bioactive constituents have been shown to confer health benefits, but their application in retinal tissue and functional vision protection in vivo remain incompletely understood. In the present study, we evaluated the influence of water-soluble, carotenoid-rich C. militaris extracts on the visual performance of light-damaged mouse retinas in vivo, using adult female CD-1® (ICR) albino mice. We showed that oral administration of this C. militaris extract (10 mg/kg, twice daily) protected the neural retina tissue against light-evoked photoreceptor cell death, reduced Müller cell hypertrophic gliosis, and elevated GSH levels and promoted the recovery of VA- and VCSF-thresholds, especially for high spatial frequency-characterized vision. These results suggest that, probably because of its water-soluble carotenoids, C. militaris extract has the potential to prevent or treat light-induced visual dysfunction.

The Functional Vision Protection Effect of Danshensu via Dopamine D1 Receptors: In Vivo Study.

Danshensu, a traditional herb-based active component (Salvia miltiorrhiza Bunge), has garnered attention, due to its safety, nutritional value, and antioxidant effects, along with cardiovascular-protective and neuroprotective abilities; however, its effect on the retinal tissues and functional vision has not been fully studied. The objective of this study was to analyze the protective effect of danshensu on retinal tissues and functional vision in vivo in a mouse model of light-induced retinal degeneration. High energy light-evoked visual damage was confirmed by the loss in structural tissue integrity in the retina accompanied by a decline in visual acuity and visual contrast sensitivity function (VCSF), whereas the retina tissue exhibited severe Müller cell gliosis. Although danshensu treatment did not particularly reduce light-evoked damage to the photoreceptors, it significantly prevented Müller cell gliosis. Danshensu exerted protective effects against light-evoked deterioration on low spatial frequency-based VCSF as determined by the behavioral optomotor reflex method. Additionally, the protective effect of danshensu on VCSF can be reversed and blocked by the injection of a dopamine D1 receptor antagonist (SCH 23390). This study demonstrated that the major functional vision promotional effect of danshensu in vivo was through the dopamine D1 receptors enhancement pathway, rather than the structural protection of the retinas.

Orthostatic blood pressure variability is associated with lower visual contrast sensitivity function: Findings from The Irish Longitudinal Study on Aging.

Hypertension is established to cause vascular end-organ damage. Other forms of dysregulated blood pressure (BP) behaviour, such as orthostatic hypotension have also been associated with cardiovascular (CV) events. The eye is potentially vulnerable to dysregulated systemic BP if ocular circulation autoregulation is impaired. We investigated whether phenotypes of abnormal BP stabilisation after orthostasis, an autonomic stressor, had a relationship with contrast sensitivity (CS), an outcome measure of subtle psychophysical visual function. This was a cross-sectional study from wave 1 of The Irish Longitudinal Study on Ageing (TILDA). From beat-to-beat orthostatic BP (BP), measured by digital photoplethysmography during active stand, 4 phenotypes have been defined 1) normal stabilisation 2) orthostatic hypotension, 3) orthostatic hypertension 4) BP variability. Contrast sensitivity was measured using a Functional Visual Analyzer. Multivariable linear regression models investigated the relationship between orthostatic BP phenotypes and contrast sensitivity in 4289 adults aged ≥50 years adjusting for, demographics, cardiovascular risk factors, self-reported eye pathologies, objective hypertension and antihypertensives. A sensitivity analysis adjusted for age-related macular degeneration, glaucoma, diabetic retinopathy and maculopathy identified on retinal photographs. Finally models were compared, adjusting for alternative measures of cataract versus not, to examine the potential effect of cataract on any associations. Systolic orthostatic BP variability was associated with worse contrast sensitivity, in the primary and the sensitivity analysis. Adjusting for alternative measures of clinical cataract attenuated the association by 18%. Orthostatic BP variability is associated with worse contrast sensitivity, independent of hypertension and retinal pathology and may be a cardiovascular biomarker of early ocular pathology.

Protective effect of crocin against the declining of high spatial frequency-based visual performance in mice

The high spatial frequency-based vision was primary on cone rich macular vision. Crocin is a major bioactive constituent of saffron (Crocus sativus L. flowers) and gardenia fruit (Gardenia spp.), which has powerful antioxidant capacities in retina. The study aim to evaluate the influence of crocin on visual performance in light-damaged mouse retinas in vivo. The visual acuity (VA), and visual contrast sensitivity function (VCSF) were measured by the behavioral optomotor reflex method. The histological changes of retinas were monitored. Both VA and VCSF declines, and that accompanied by Müller cell hypertrophic gliosis and cone cellular damage were detected in the vehicle groups. Prophylactic crocin treated groups improved VA and VCSF on sensitive to high spatial frequency, protected retinal integrity and Müller cells, and modulated the cellular function of cone. This study provides the potential use of crocin to ameliorate the visual performance due to its anti-photodamage and cytoprotective effects.

Decreased glucose-6-phosphate dehydrogenase activity along with oxidative stress affects visual contrast sensitivity in alcoholics.

To evaluate oxidative stress and glucose-6-phosphate dehydrogenase (G6PD) status of alcoholics and discern their association, if any, with visual contrast sensitivity function. Forty male alcoholic subjects and 36 male non-alcoholic subjects with the same age and nutritional status were enrolled in this study. Serum malondialdehyde (MDA) level and glucose-6-phosphate dehydrogenase (G6PD) activity of erythrocytes were determined by spectrophotometric assay. Contrast sensitivity (CS) function of study subjects was measured using the Rabin Contrast Sensitivity Test (Precision Vision®, La Salle, Illinois, United States). Serum MDA levels were significantly higher (p<0.0001) and erythrocyte G6PD activity was significantly lower (p=0.0026) in alcoholic subjects compared to the controls. CS scores of both eyes were also found to be decreased significantly in alcoholic subjects (both at p<0.0001) compared to control subjects. On the other hand, CS scores of the alcoholic subjects were inversely correlated with the serum MDA level (r=-0.746, p<0.0001) and directly correlated with erythrocyte G6PD activity (r=0.78, p<0.0001). A strong inverse correlation (r=-0.84, p<0.0001) was also observed between serum MDA level and erythrocyte G6PD activity of alcoholic subjects. Reduced G6PD activity and increased serum MDA level might be the key cause of the early visual abnormalities, such as reduced CS function of the alcoholic subjects.

No-Reference Quality Assessment of Noise-Distorted Images Based on Frequency Mapping

In this paper, we propose a no-reference image quality assessment (IQA) metric for noise-distorted images specifically based on frequency mapping (FM), namely, FMIQA index. First, we decompose the image into intrinsic mode functions (IMFs) from small to large scale by using bidimensional empirical mode decomposition (BEMD), and perform the local feature analysis on the IMFs by Riesz transform. Considering that the combination of BEMD and Riesz transform can denoise the noise-distorted image, we use this method with appropriate application of visual contrast sensitivity function to get the denoised image. Then we calculate the similarity map of the Riesz transform feature maps from the distorted image and the denoised image to obtain the similarity indices. Finally, we combine these similarity indices to obtain the final index. Experimental results on three public databases show that the proposed FMIQA evaluates the noise-distorted image in consistency with subjective assessment and can obtain better performance in image quality prediction than other existing related methods.

High Frame Rates and Human Vision: A View through the Window of Visibility

There is new interest in higher frame rates for digital cinema. The frame rate and subsequent processing have a large impact on the presence of artifacts in the final presentation. The structure of these artifacts is revealed by transforming the sequence of frames into the spatiotemporal frequency domain. The visibility of these artifacts can be determined through application of a tool called the window of visibility. This is a simplified representation of human visual sensitivity to spatial and temporal frequencies. This paper describes the capture and display of movies in signal processing terms. It shows how the several steps in the process can by represented in space and time and in spatial and temporal frequency. It then introduces the window of visibility as a simplified version of the human visual contrast sensitivity function. It shows how the tool can be used to compute the lowest artifact-free frame rate under simplified circumstances. It also shows how it can be used to visualize the impact of various steps in processing the image sequence. Finally, the paper describes the influence of luminance, eccentricity, color, and eye movements on the size and shape of the window of visibility. In conclusion, the tool provides a useful aid to understanding the role of human visual sensitivity in the selection of frame rates and frame processing. The paper also provides an interactive demonstration that allows exploration of the trade-offs in movie capture and display.

Neural correlates of stimulus spatial frequency-dependent contrast detection

Psychophysical studies on human and non-human vertebrate species have shown that visual contrast sensitivity function (CSF) peaks at a certain stimulus spatial frequency and declines in both lower and higher spatial frequencies. The underlying neural substrate and mechanisms remain in debate. Here, we investigated the role of primary visual cortex (V1: area 17) in spatial frequency-dependent contrast detection in cats. Perceptual CSFs of three cats were measured using a two-alternative forced-choice task. The responses of V1 neurons to their optimal visual stimuli in a range of luminance contrast levels (from 0 to 1.0) were recorded subsequently using in vivo extracellular single-unit recording techniques. The contrast sensitivity of each neuron was determined. The neuronal CSF for each cat was constructed from the mean contrast sensitivity of neurons with different preferred stimulus spatial frequencies. (1) The perceptual and neuronal CSFs of each of the three cats exhibited a similar shape with peak amplitude near 0.4 cpd. (2) The neuronal CSF of each cat was highly correlated with its perceptual CSF. (3) V1 neurons with different preferred stimulus spatial frequencies had different contrast gains. (1) Contrast detection of visual stimuli with different spatial frequencies may likely involve population coding of V1 neurons with different preferred stimulus spatial frequencies. (2) Difference in contrast gain may underlie the observed contrast sensitivity variation of V1 neurons with different preferred stimulus spatial frequencies, possibly from either evolution or postnatal visual experiences.

Update of Residential Tetrachloroethylene Exposure and Decreases in Visual Contrast Sensitivity

Update of Residential Tetrachloroethylene Exposure and Decreases in Visual Contrast Sensitivity

On the optical theory of underwater vision in humans

Defocus changes the visual contrast sensitivity function, thereby creating a complex curve with local dips and peaks. Since underwater vision in humans is severely defocused, we used optical theory and the phenomenon of spurious resolution to predict how well humans can see in this environment. The values obtained correspond well with experimental measurements of underwater human acuity from earlier studies and even point to an opportunity for humans with exceptional contrast sensitivity to see better underwater than the children in those studies. The same theory could be useful when discussing the visual acuity of amphibious animals, as they may use pupil constriction as a means of improving underwater vision.

Application of a noise-adaptive contrast sensitivity function to image data compression

The visual contrast sensitivity function (CSF) has found increasing use in image compression as new algorithms optimize the display- observer interface in order to reduce the bit rate and increase the perceived image quality. In most compression algorithms, increasing the quantization intervals reduces the bit rate at the expense of introducing more quantization error. The CSF can be used to distribute this error as a function of spatial frequency such that it is undetectable by the human observer. Thus, instead of being mathematically lossless, the compression algorithm can be designed to be visually lossless, with the advantage of a significantly reduced bit rate. However, the CSF is strongly affected by image noise, changing in both shape and peak sensitivity. This work describes a model of the CSF that includes these changes as a function of image noise level by using the concepts of internal visual noise. The model is tested in the context of image compression with an observer study.

The objective assessment of contrast sensitivity function by electrophysiological means.

In recent years it has been shown that it is of considerable clinical value to determine the visual contrast sensitivity function of the patient. This can reveal the wider effects of pathology on the visual system where visual acuity may or may not be affected. There is a comprehensive literature on subjective approaches of obtaining this function in the clinical environment but very little on alternative objective methods. This paper describes the latter approach, which exploits electrophysiological techniques using the visual evoked cortical potential (VECP) to checkerboard onset-offset stimulation. Its application in a variety of disorders of the visual system is described. The importance of selecting the most appropriate stimulus parameters is discussed, and the relative advantages and disadvantages as compared with psychophysical methods are appraised.

Detectability of low-contrast features in computed tomography

Factors affecting low-contrast feature detectability in computed tomography have been investigated using signal detection experiments. Detectability of a circular object in a uniform noise field was found to increase with decreasing window width. With increasing viewing distance, detectability increased to a maximum before decreasing; the optimal viewing distance was found to increase with decreasing window width. Detectability was independent of window level and image luminance, over the range of values studied. A mathematical model of the CT display system and the human visual system was constructed, using empirical transfer characteristics as system descriptors and an optimal matched filter model of pattern recognition. Theoretical signal-to-noise ratios were in qualitative agreement with the experimental data when account was taken of the visual contrast sensitivity function and the effect of noise internal to the observer. Quantitative discrepancies suggest either that visual matched filter processing is sub-optimal, or that use of the contrast sensitivity function as a spatial filter is only approximately valid. Compared with the visual system characteristics, those of the display system were insignificant. Modifications to CT display configurations are suggested in order to maximise information transfer between the display system and the visual system of the radiologist.

Optical characteristics of Transpaseal as a partial occluder.

The acuity degradation produced by Transpaseal, a typical adhesive scattering material applied to spectacle lenses to produce partial occlusion during orthoptic treatment, is studied by measuring the angular characteristics of the scattering and its effect upon the visual contrast sensitivity function. Whereas in general the material acts as a low-pass spatial frequency filter, it is shown that the scattering function is not symmetrical and hence that the visual degradation produced varies with the orientation of the detail observed.

Development of contrast sensitivity in infant Macaca nemestrina monkeys.

During an infant monkey's first 28 postnatal weeks, the visual contrast sensitivity function develops its characteristic adult form. Contrast sensitivity is depressed relative to that of the adult for all spatial frequencies during the early postnatal weeks. Absolute sensitivity to frequencies below 5 cycles per degree approaches adult levels by 20 weeks after birth, whereas sensitivity to fine spatial detail continues to develop through 28 weeks. The results imply that the development of primate spatial vision is more complex than just an improvement in the ability to resolve acuity gratings.

Visual contrast sensitivity functions obtained with colored and achromatic gratings.

Threshold contrasts for red, green, and achromatic sinusoidal gratings were measured. Spatial frequencies ranged from 0.25 to 15 cycles/deg. No significant differences in contrast thresholds were found among the three grating types. From this finding it was concluded that, under conditions of normal viewing, no significant differences should be expected in the acquisition of spatial information from monochromatic or achromatic displays of equal resolution.