Contrast sensitivity in multiple sclerosis measured by Cambridge Low Contrast Gratings: a useful clinical test?

SUBCLINICAL OPTIC NEURITIS

Acute optic neuritis is often associated with multiple sclerosis. It is considered to be the most common ocular symptom of multiple sclerosis. In addition to acute optic neuritis, in patients with multiple sclerosis, subclinical optic neuritis is also described. It is characterized by slow progression and bilateral involvement, thus being unnoticed by the patient. The purpose of the present study was to assess vision impairment in multiple sclerosis patients without a history of acute optic neuritis, using a number of functional tests including visual field testing by Octopus 101 perimetry N1 program, contrast sensitivity testing by Pelli Robson chart, and color vision by Ishihara pseudoisochromatic plates. The study included 35 multiple sclerosis patients aged 18-50 years, without subjective signs of vision impairment and visual acuity 1.0 according to Snellen. Visual field defects were found in 28 patients. The most common defects of visual fields were retinal sensitivity depression in peripheral zone and nerve fiber bundle defect. Reduced contrast sensitivity was found in 30 (86%) patients. Study results indicated multiple sclerosis patients free from signs of optic neuritis to suffer vision function impairment, as demonstrated by Octopus perimetry and contrast sensitivity testing with Pelli Robson charts.

The initial visual performance modulates the effects of anodal transcranial direct current stimulation over the primary visual cortex on the contrast sensitivity function

Transcranial direct current stimulation (tDCS) has great potential to modulate cortical excitability and further facilitate visual function or rehabilitation. However, tDCS modulation effects are largely variable, possibly because of the individual differences in initial performance. The present study investigated the influence of the initial performance on contrast sensitivity function (CSF) following tDCS. Fifty healthy participants were randomly assigned to three groups: anodal, cathodal and sham stimulation. The CSF was measured through a grating detection task before and immediately after tDCS. Active and reference electrodes were applied to the primary occipital cortex (Oz) and the middle of the head (Cz) for 20 min with an intensity of 1.5 mA, respectively. Compared with sham stimulation, anodal or cathodal stimulation had no effect on the area under the log CSF (AULCSF) or contrast sensitivity (CS) of various spatial frequencies at the group level. However, a negative relationship was found between initial performance and the AULCSF change (or CS change at a spatial of frequency 8 c/°) after the application of anodal tDCS, indicating that the degree of change was dependent on initial performance, with greater gains observed for those with poorer initial performance. Initial performance modulated the effect of anodal tDCS over the Oz on the CSF, indicating that the Oz plays a crucial role in visual function. These results contribute to a deep understanding of the mechanisms of tDCS and to the design of more precise and efficient personalized simulation approaches based on individual differences.

Reduced Contrast Sensitivity Function in Central and Peripheral Vision by Disability Glare

Various glares can decrease visual performance and cause discomfort, thus increasing drivers' risk for traffic accidents in real life. The current study aimed to systematically investigate glare sensitivity in the central and peripheral visual fields by measuring contrast sensitivity function (CSF) under nonglare, steady glare, and transient glare conditions. Nine observers with normal visual acuity in the dominant eye were enrolled. The CSF in central and peripheral vision (the 5° upper left visual field) was measured in a mesopic environment while the stimulus was displayed under three conditions: nonglare, steady glare, and transient glare. An orientation identification task was used to obtain the CSF. After the experiment, the observers were asked to report their level of discomfort in the presence of the glare. The area under the log CSF (AULCSF) and cut-off spatial frequency served as indicators of visual performance. In agreement with previous studies, both steady and transient glare reduced the AULCSF and cut-off frequency. However, the AULCSF and cut-off frequency were reduced more for central vision than for nearly peripheral vision. In addition, the extent of the decreases in the AULCSF and cut-off frequency was greater for steady glare than for transient glare; in contrast, more discomfort was associated with transient glare than steady glare.

Influence of multiple sclerosis, age and degree of disability, in the position of the contrast sensitivity curve peak

Context:

Contrast sensitivity (CS) function is one of the most important tests available for evaluating visual impairment. Multiple sclerosis (MS) can produce highly selective losses in visual function and psychophysical studies have demonstrated CS deficits for some spatial frequencies.

Aims:

This work studies the differences in CS between a group of controls and a group of MS patients, focusing on the location of the maximum sensitivity peak, shape of the curve, and determination of the most affected spatial frequencies.

Materials and Methods:

Using a sinusoidal stimulus the authors assessed CS function in 28 subjects with definitive relapsing remitting MS, and in 50 controls with acuities of 20/25 or better. The peaks of the CS curves were studied by fitting third degree polynomials to individual sets of data.

Results:

Compared with the control group, the CS function curve for MS subjects showed more deficits in extreme points (low- and high-spatial frequencies). Our results display significant CS losses, at the high-frequencies band level, in the beginning of the disease. When the disease progresses and the disabilities appear, there are greater losses at the low-frequencies band level. In average, the CS curve peaks for the MS group were shifted in relation to the control group.

Conclusions:

CS losses in the MS group suggest an association with ageing and disability level in the expanded disability status scale. The position of the CS function peak is influenced by MS, age, and degree of disability.

Contrast Sensitivity versus Visual Evoked Potentials in Multiple Sclerosis

PURPOSE

To compare the Cambridge contrast sensitivity (CS) test and visual evoked potentials (VEP) in detecting visual impairment in a population of visually symptomatic and asymptomatic patients affected by clinically definite multiple sclerosis (MS).

METHODS

Fifty patients (100 eyes) presenting with MS and 25 healthy subjects (50 eyes) with normal corrected visual acuity were included in this study. CS was determined using the Cambridge Low Contrast Grating test and VEP was obtained in all eyes. Findings were evaluated in two age strata of 10-29 and 30-49 years.

RESULTS

Of the 42 eyes in the 10-29 year age group, CS was abnormal in 22 (52%), VEP was also abnormal in 22 (52%), but only 12 eyes (28%) had visual symptoms. Of the 58 eyes in the 30-49 year group, CS was abnormal in 7 (12%), VEP was abnormal in 34 (58%), while only 11 eyes were symptomatic. No single test could detect all of the abnormal eyes.

CONCLUSION

The Cambridge Low Contrast Grating test is useful for detection of clinical and subclinical visual dysfunction especially in young patients with multiple sclerosis. Nevertheless, only a combination of CS and VEP tests can detect most cases of visual dysfunction associated with MS.