Top PDF Contrast Sensitivity Studies and Test- Review

Contrast Sensitivity Studies and Test- Review

Contrast Sensitivity Studies and Test- Review

Many conditions (age, myopia, etc.) and eye diseases (diabetes, cataract, glaucoma, etc.) affect CS, just before any change in V.A. is detected. Studies around the world have been conducted by various researchers on CS changes depending on the case and the effect this change has on patients’ daily lives. With age, the functions of the body begin to decline and so does CS. Although it has generally not been established by studies in patients with good visual acuity, what exactly neurological changes in age contribute to the loss of CS[22].The frequencies initially affected are the lowest and begin at approximately after the age of 40 [22]. Although myopia is a refractive error, it is a significant factor in effecting CS of the eye. Several studies show that there is a decrease in CSF in myopia, but the role of refractive error is unclear, as various optical factors, such as eye aberration (spherical aberration, diffusion by the crystalline lens), are inserted [23-25].The retina and the macula area are affected by several diseases, such as age-related macular degeneration, diabetes, detachment, central serous retinopathy, macular holes, etc. CS appears weakened to a degree regarding the severity of the disease [26-30]. For example, in the case of macular holes, the less tissue missing, the closer the CS is to the normal (but not completely normal) [30].Nevertheless, CS is definitely affected and usually before V.A. of the patient, in the early stages of the disease (age-related macular degeneration, diabetic retinopathy), causing problems in his quality of the patient life (driving, working etc.) [27,31,32]. In the retinal diseases category there are also studies with positive CS results. In some situation it is possible to recover part of the lost CS by restoring the tissue, such as retinal detachment, following surgery [28] or in cases of diabetic macular edema resection [6,32].
Show more

7 Read more

Magnetic resonance imaging for detecting root avulsions in traumatic adult brachial plexus injuries: protocol for a systematic review of diagnostic accuracy

Magnetic resonance imaging for detecting root avulsions in traumatic adult brachial plexus injuries: protocol for a systematic review of diagnostic accuracy

There are many potential sources of bias in the studies of diagnostic accuracy [49]. We expect a mi- nority of patients with BPI will not have undergone operative exploration for various reasons, e.g. they did not consent to surgery, anaesthesia was unsafe or the treatment of other injuries took precedence. This would upwardly bias the sensitivity of MRI if the pro- portion of false negatives is underestimated. This problem cannot be reliably mitigated by replacing or supplementing exploratory surgery with another refer- ence standard, e.g. clinical observation because (a) the reanimation of the limb may evolve over several years and concurrent stiffness and contractures may prevent reliable and repeatable inferences about function; (b) testing a given muscle in isolation (and thus the sup- plying root) may be impossible as many movements involve several muscles working in synergy, each re- ceiving input from different nerves and thus, different cervical roots; (c) cerebral cortical reorganisation may undermine clinical observations of muscle power and sen- sation, e.g. where two roots supply one muscle and one is injured, the cortex may reroute more input to the remaining fibres, confounding the assessment of function; and (d) the end organs of the limb (muscles, skin, joints, tendons, etc.) may receive input from several roots and equally, one root may innervate several structures, so the constellation of clinical abnormalities cannot be confidently attributed to a specific site of injury. In contrast, the diag- nostic accuracy of MRI may be downwardly biased because patients may have been referred based on MRI findings ra- ther than the presence of symptoms alone. We also expect most studies to be retrospective, and some studies may have recruited an unrepresentative sample of patients which may bias diagnostic accuracy and raise con- cerns about applicability. These and other issues will be addressed in the quality assessment, and we will interpret the findings of our review with respect to these potential limitations.
Show more

6 Read more

Contrast sensitivity deficits in patients with mutation-proven inherited retinal degenerations

Contrast sensitivity deficits in patients with mutation-proven inherited retinal degenerations

In this study, we demonstrated that patients with IRD have significant deficits in CS when visual acuity is relatively pre- served. By using the QCSF test, we also showed that CS in these patients is reduced in all spatial frequencies. We also found the greatest reductions in CS at the higher spatial fre- quencies (from 6.0 to 18.0), which is consistent with previous studies [19]. These changes may be missed by Pelli-Robson testing which at fewer spatial frequencies. Furthermore, pa- tients with STGD had worse CS than patients with the other IRDs, even though visual acuities were similar between IRD subgroups. Our study therefore indicates that CS is not merely a surrogate for visual acuity, as it can provide more information about visual dysfunction in these patients than visual acuity alone.
Show more

6 Read more

The importance of contrast sensitivity testing in children

The importance of contrast sensitivity testing in children

literature suggesting that this does not apply to a child’s visual system. Evaluating remaining functional vision such as CS and VA in both children and adults with severe vision loss is key when determining rehabilitative strategies and quality of life. Overall, studies have shown that the assessment of other spatial vision measures contributes additional information to that provided by acuity alone. 2–3,5,12–14

6 Read more

Evaluation of contrast sensitivity and other visual function outcomes in neovascular age-related macular degeneration patients after treatment switch to aflibercept from ranibizumab

Evaluation of contrast sensitivity and other visual function outcomes in neovascular age-related macular degeneration patients after treatment switch to aflibercept from ranibizumab

When reviewing the results of our study, differences in participant selection, baseline features, and inclusion criteria limit generalizability and direct comparisons between reported anti-VEGF switch studies in neovascular AMD. The sample size of the switch cohort in this study was relatively small, many patients had received chronic long-term ranibi- zumab treatment, and follow-up of participants was limited at 12 weeks only. Comparative analyses involving a control arm of patients continuing on ranibizumab despite recur- rent or persistent fluid might have strengthened the overall analysis. A crossover study design incorporating a reswitch arm from aflibercept back to ranibizumab may be a useful consideration in the development of future anti-VEGF treat- ment switch studies. It would also be of interest to conduct a larger study to evaluate long-term outcomes, including the potential for greater improvement in vision-related functional benefit with continuing treatment, after a treatment switch to aflibercept from ranibizumab.
Show more

7 Read more

Fuzzy Logic based watermarking using non – blind HVS technique

Fuzzy Logic based watermarking using non – blind HVS technique

With the increase in the availability of digital data over internet, the images so distributed can be copied repeatedly with or without error, putting the rights of owner at risk. One way to arrest illegal duplication is to in-sert owner’s identity known as watermark into potentially vulnerable images so that watermarks are inseparable from the images itself. The important requirements of watermarking [1] are centered on three main issues -These are imperceptible quality of watermarked and attacked images, robustness and embedding capacity. Among these the former two parameters are important and these are found to be mutually conflicting. Because of this water-marking may be perceived as an optimization problem to obtain robust embedding and extraction scheme. This paper addresses the problem by constructing fuzzy perpet- ual masks. Human Visual System is the ultimate receiver of most processed images. Incorporating. Just Noticeable Difference (JND) provides a means to model perpetual redundancy that is the maximum distortion which cannot be perceived by human eye. In [6]-[8] JND thresholds are computed based on background luminance adaption and spatial contrast masking. In [2] a more accurate JND map is deduced considering
Show more

6 Read more

Analysis of visual function and quality of life in patients with uveitis

Analysis of visual function and quality of life in patients with uveitis

In general, the methods recommended to measure contrast sensitivity include: simple plates, cathode ray tube display on a screen, letter acuity charts, laser interferometer (LI) which produces grating on the retina, visual field testing using low contrast rings on stimuli, pattern discrimination test, prototype for forced choice printed test, visually evoked cortical potentials to checkerboard pattern reversal dependent contrast threshold measurement, two-alternative forced choice test and many more.

159 Read more

Quality of Financial Reporting, Investment and Quality of Disclosure: With Stressing on Type of Financing

Quality of Financial Reporting, Investment and Quality of Disclosure: With Stressing on Type of Financing

statistic value of Durbin-Watson test is about 2 (nearly 2 ± 0.5), it means that the sample is random and represents the lack of self-correlation. Pearson correlation coefficient is also investigated between variables. Coefficients of regression model variables are tested using T-student test. In this study, Durbin- Watson test is used to test the overall significance of regression model fitted to the Fisher statistic (F) in 95% confidence level as well as to test the lack of correlation between errors of the model. At the end, the error components curve was plotted in regression model to assess normality of error components. Using linear regression (Linear-Regression) we will test the hypotheses. In this study, the multivariate regression method will be used as statistical method and panel data. In the regression, the main objective is to examine whether there is a relationship between dependent and independent variables or not. Moreover, data analysis in descriptive statistics will be started by calculating central parameters including mean, median and distribution indexes of standard deviation, skewness and skewness elongation. These indicators will be conducted by separate industries and as a whole. After necessary corrections and classification based on variables, collected data entered Spss software using Excel software and the final analysis will be conducted. Ultimately, we will focus on confirming or refusing the research hypotheses using the results of Spss and EViews 7 software.
Show more

15 Read more

Mesopic Visual Contrast Sensitivity in Patients with Major Depression

Mesopic Visual Contrast Sensitivity in Patients with Major Depression

Changes in visual CS caused by major depression were ex- pected in the present study, based on studies that reported that neuropsychiatric disorders affect cognition and central nervous system function (Bubl et al., 2010; Duman, Heninger, & Nes- tler, 1997; O’Donnell et al., 2002; Slaghuis, 1998; Wolman & Stricker, 1990). Some studies used electrooculography (EOG) (Lam et al., 1991; Fountoulakis, Foutiou, Iacovides, & Kaprinis, 2005) and flash electroretinography (ERG) (Fountoulakis et al., 2005; Hébert et al., 2004; Lavoie et al., 2009) to evaluate pa- tients with seasonal depression and reported the presence of changes in the retina at the photoreceptor level, which resulted in decreased light sensitivity in depressive patients compared with the control group. Both EOG and ERG are useful tools, the results of which indirectly reflect dopamine activity in the retina. Several studies have related decreased dopamine activity with specific depressive symptoms. For example, Harris, Cal- vert, Leendertz e Phillipson (1990) suggested that lower dopa- mine levels in the brain in depressed patients result in a de- crease in visual CS. Bodis-Wollner e Tzelepi (1998) proposed that dopamine D 2 receptors affect the ability to visually detect
Show more

5 Read more

THE DEVELOPMENT OF A GENDER-SENSITIVITY TEACHING TEST

THE DEVELOPMENT OF A GENDER-SENSITIVITY TEACHING TEST

Five variables loaded on this factor with an explained variance of 16.242%. The researchers named this factor as “gender equality” which explains the importance of every teacher to treat everyone fairly and equally regardless of gender. The indicators (items 14, 16, 7, and 5) under the third dimension could be deliberated in the second factor or the indicator, item number 3, in the first Factor. However, this dimension should be treated as necessary as the other two factors for this emphasizes the need to foster respect and promote gender equality in all aspects and processes in teaching and learning. It is noteworthy that in all of the five items loaded on this factor, the idea of equality is explicitly expressed, namely: holds the same academic and behavioral expectations… (item 14), provides equal praise, punishment, and other disciplinary measures… (item 16), provides students with equal opportunities for class participation… (item 7), accepts and treats all students in class without bias… (item 3), and creates a classroom environment that supports equal opportunities for all students regardless of gender (item 5). This only highlights the relevance of this construct as an essential construct in measuring gender- sensitivity in teaching. Evaluate the Items. The final statistical analysis for the data was the coefficient alphas for each factor using Cronbach‟s alpha [14]. Table 5 below shows that the three factors in the developed tool have a coefficient of more than 0.90. This strongly indicates good internal reliability among the items of each factor.
Show more

8 Read more

Motion processing deficits in migraine are related to contrast sensitivity

Motion processing deficits in migraine are related to contrast sensitivity

For motion discrimination trials, a percentage of the dots moved in a coherent direction (up or down) for 300 ms while the remainder moved in random directions. On consecutive trials, the percentage of dots moving coherently was either decreased or increased, depending on whether the preceding response had been correct or incorrect. A two down, one up staircase procedure was used to converge upon a threshold coherence corresponding to a 71% correct discrimination rate (35, 36). The two-down, one-up staircase procedure, and the resulting 71% threshold discrimination rate, were chosen to achieve a reasonable estimate of threshold without needing an excessive number of trials. Two staircases were interleaved, both starting at 70% coherence. An initial step size of 10% was reduced to 1% after 3 staircase reversals. The practice blocks of trials terminated after a minimum of 2 reversals for each staircase in the four conditions. For the experimental trials, each block of trials was terminated after a minimum of 8 reversals for each staircase in the four conditions. Condition order [display density (50 or 300 dots) and display contrast (low or high)] was randomised for each
Show more

39 Read more

Visual resolution and contrast sensitivity in two benthic sharks

Visual resolution and contrast sensitivity in two benthic sharks

The information content of vision is, to a large extent, determined by the spatial resolving power and contrast sensitivity of the eye (Eckert and Zeil, 2001; Land and Nilsson, 2012). Both contrast sensitivity and spatial resolving power influence an animal ’ s ability to discriminate objects against a background and affect the distance at which detection can occur (Land, 1999; Eckert and Zeil, 2001). Anatomical estimates of spatial resolving power have been obtained for a number of shark species and range from two to 11 cycles per degree (cpd) (Hueter, 1990; Lisney and Collin, 2008; Litherland and Collin, 2008). However, no estimates of contrast sensitivity or behavioural estimates of spatial resolution currently exist, suggesting that categorising sharks as having ‘ poor ’ vision may be presumptuous. In aquatic environments, absorption and light scattering strongly affect the visual contrast of an object as the distance from the observer increases (Lythgoe, 1980, 1988; McFarland, 1990; Land and Nilsson, 2012). Thus, underwater contrast, rather than spatial resolving power, is often the limiting factor in the early detection and identification of objects. Sharks may trade off spatial resolving power and enhance contrast sensitivity.
Show more

10 Read more

Sensitivity of test of significance   problem posed

Sensitivity of test of significance problem posed

We wish to decide from the sample, using the test c, whether in the population the value of /x could plausibly be taken as zero hypothesis H„ or whether /x has probably some value greate[r]

10 Read more

The spectral, spatial and contrast sensitivity of human polarization pattern perception

The spectral, spatial and contrast sensitivity of human polarization pattern perception

Spatial resolution for grating patterns and Landolt C optotypes. The solid symbols in Fig. 4a show the contrast sensitivity measures, averaged across six observers, for discriminating the orientation of polarization-modulated square-wave gratings as a function of grating periodicity (cpd). For comparison, sensi- tivity measures are also shown for luminance-modulated gratings (open symbols). All measures were obtained using a backlighting filtered to a waveband peaking at 460 nm, chosen to approximate the maximum spectral sensitivity of human polarization vision (see Supplementary Material Figure S2). Note that, over the range of val- ues assessed, contrast sensitivity for polarization-modulated patterns is an order of magnitude less than that for luminance-modulated patterns. When plotted on logarithmic co-ordinates, an exponential function provided an excellent fit (R 2 > 0.95) to the decline in sensitivity at higher spatial frequencies 27 (continuous line through each
Show more

10 Read more

The effect of pterygium surgery on contrast sensitivity and corneal topographic changes

The effect of pterygium surgery on contrast sensitivity and corneal topographic changes

Patient and methods: The IRB approved this prospective, nonrandomized, self-controlled study. Computerized videokeratography (Orbscan II) was performed in 36 patients with primary pterygia, both before and 1 month after pterygium excision with limbal-conjunctival autografting. The topographic parameters were compared. Spatial contrast sensitivity testing was performed using VCTS 6500. Differences between preoperative and postoperative values were evaluated statistically.

5 Read more

Miniaturisation reduces contrast sensitivity and spatial resolving power in ants

Miniaturisation reduces contrast sensitivity and spatial resolving power in ants

Although the smallest ant in our study, R. inornata, had 8% of the facets of the largest ant, M. tarsata, it still had 80% of their spatial resolution but only 8% of their contrast sensitivity. This suggests that R. inornata requires spatial resolving power more than contrast sensitivity. This also indicates that spatial resolution and contrast sensitivity do not decrease similarly with size. The reduced contrast sensitivity can also be attributed to the decreased number of facets, with M. nigrocincta being an outlier given their unique foraging behaviour, as discussed earlier. Smaller individuals of Drosophila melanogaster have sacrificed contrast sensitivity to improve spatial resolution (Currea et al., 2018). But these flies rely on temporal summation to improve contrast sensitivity. Increased integration duration of photoreceptors enhances visual sensitivity by increasing photon capture, signal to noise ratio and contrast discrimination (Warrant, 1999). To determine whether this was the case in our ants, from our electroretinogram recordings of the largest and smallest ant, we measured the duration of the ON response (first peak in Fig. 6) as the full-width of the response at half the maximum amplitude. The duration of the ON response was short in M. tarsata (106.95±3.84 ms; n=4) compared with that in R. inornata (261.35±53.49 ms; n=4). This shows that R. inornata have longer integration times, which may allow them to improve their low contrast
Show more

10 Read more

The improvement of contrast sensitivity with practice is not compatible with a sensory threshold account

The improvement of contrast sensitivity with practice is not compatible with a sensory threshold account

For each observer in each condition, we regressed maximum- likelihood estimates of threshold (in dB) and slope (Weibull β ) against the day of testing. For each observer and each day, lapse rates ( δ ) were fixed at the values determined from the high-contrast/no- noise trials (or 0.01; whichever was larger). Without exception, the line best fit to every observer's detection thresholds in the absence of noise had a negative gradient (see Fig. 4a). Across the group, the mean and standard error of the fitted slopes were –0.72 and 0.15 dB/day, respectively. Thus, there can be no question that our methods were sufficient to elicit a significant facilitatory effect of practice on contrast sensitivity, t(8) = –4.93, p < 0.001.
Show more

12 Read more

Elevated sensitivity to tactile stimuli in stereotypic horses

Elevated sensitivity to tactile stimuli in stereotypic horses

The statistical analyses were carried out on the behavioral parameters for which the inter-observer reliability (ICC) between the two observers was fair to excellent (ICC: mean ± SD = 0.84 ± 0.14; range = 0.55–0.98). The behavior of the crib-biters (CB) was compared to the behavior of the control horses (C) for each test separately (Tables 2, 3), using linear mixed-effects models (LMM; lmer function, lme4 library), generalized linear mixed models [GLMM; glmer function; lme4 library; multcomp library; (77)], or cumulative link mixed models [CLMM, clmm function in R 3.0.2 (78)]. The different models included as a response variable the behavioral parameters scored (Tables 2, 3). The fixed and control factors are described in Tables 2, 3. To control for repeated measurements of the same subjects, the identity of the horses nested within the farms where they were housed (“Farms”) was included as a random factor for Tests 2 and 4. For Test 1, Test 5, and for the locomotor activity, only Farms was included as a random factor, as there was only one behavioral value for each horse. When significant interaction effects between fixed and/or control factors were found, further post-hoc analysis were carried out using further LMMs and GLMMs. Bonferroni corrections were applied to these post-hoc tests accordingly.
Show more

14 Read more

Diagnostic value of ultrasound in calcium pyrophosphate deposition disease: a systematic review and meta analysis

Diagnostic value of ultrasound in calcium pyrophosphate deposition disease: a systematic review and meta analysis

Our report is the fi rst systematic review with meta-analysis to examine diagnostic performances of US in CPPD. Although its incidence and prevalence remain unclear, CPPD is a frequent disease with currently no real pharmacological option to address the crystal forma- tion and dissolution. 27 Since the clinical presentation of CPPD can vary and can mimic other rheumatic diseases, its detection relies on the accuracy of the imaging tech- nique used. US has growing importance in the fi eld of rheumatology and speci fi cally in crystal-related arthropa- thies. After an exhaustive search of the scienti fi c litera- ture, we found several studies of the diagnostic value of US in CPPD, but they included a small number of patients and controls. The meta-analysis allowed us to pool these studies and improve the power.
Show more

8 Read more

Critical duration, contrast sensitivity, and specific reading disability

Critical duration, contrast sensitivity, and specific reading disability

In view of the evidence on spatial frequency-specific temporal properties in visual processing, the possibility of abnormal interaction, in SRD children, of spatial frequency channels, b[r]

106 Read more

Show all 10000 documents...

Related subjects