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PubMed2003

Contrast sensitivity after +Gz acceleration.

BACKGROUND: This study was designed to determine the extent and duration of contrast sensitivity (CS) loss after high sustained +Gz acceleration in a centrifuge. METHODS: The subjects were 12 healthy male flight surgeons between 20 and 22 (mean = 21.1) yr of age. The human centrifuge at the Aviation Physiology Research Laboratory in Tainan, Taiwan, was used to expose the subjects to an acceleration profile. Each subject experienced three centrifuge runs made up of one gradual onset and two rapid onset profiles. Contrast sensitivity (CS) was measured before, and at 5 min, 10 min, and 20 min for the right eye; and 7 min, 12 min, and 22 min for the left eye after the acceleration. Both eyes were measured with the right eye being tested first. RESULTS: There was a generalized depression of CS at 5-12 min for both eyes. The depression was more severe at low and medium frequencies (1.5, 3.0, 6.0 cycles per degree, cpd) than at a high spatial frequency (18.0 cpd). There was a significant decrease in CS of the right eye at 1.5 cpd (p < 0.05 between control and 5 min), and on the left eye at 3.0 cpd (p < 0.05 between control and 7 min, p < 0.05 between control and 12 min) and 6.0 cpd (p < 0.05 between control and 12 min). The CS loss was more obvious at 5-12 min for both eyes, and there was only partial recovery at 22 min after the acceleration. CONCLUSIONS: These results demonstrated that +Gz acceleration is associated with CS loss. The recovery time was greater than expected. Factors other than ocular blood flow may be involved in the prolonged CS loss.

Adult↗

PubMed1987

Changes in contrast sensitivity during the first six months of soft lens wear.

Changes in the contrast sensitivity function (CSF) and corneal thickness of six subjects were monitored during the first 6 months of soft lens wear. Contrast sensitivity suffered a temporary reduction during the first two weeks of wear, subsequently recovering rapidly to normal baseline levels. Corneal thickness increased by 4.9% on the first day of wear, thereafter gradually returning to, but never attaining, prefitting levels. No evidence was found to support complaints of poor vision by long-term soft lens patients. The etiology of the contrast decrements revealed in the early (or adaptation) stages of soft lens wear is discussed.

Adolescent↗

PubMed1998

Peripheral and central factors limiting the development of contrast sensitivity in macaque monkeys.

The aim of this study was to evaluate the contribution of peripheral and central factors to the development of visual sensitivity. We used the approach of (Pelli, 1981, 1990) to evaluate the hypothesis that intrinsic noise is high in infants compared with adults, and therefore sets an important limit on contrast sensitivity in infants. We measured contrast thresholds in the presence of various levels of dynamic spatiotemporal broadband noise in infant monkeys, and evaluated the developmental changes in contrast threshold and intrinsic noise. Our data show that intrinsic noise is high in infants and falls with contrast threshold during development. However, contrast thresholds in high-contrast noise also fall during development, although by a smaller amount. Therefore, while changes in intrinsic noise set an important limit on the development of contrast sensitivity across spatial frequencies, changes in non-additive sources of noise also contribute, particularly at high spatial frequencies. We interpret these results in terms of Pelli's hypothesis about the sources of additive and non-additive noise affecting visual detection. In these terms, additive noise reflects peripheral factors and non-additive noise reflects central ones. Our results suggest that changes in peripheral sources of noise represent an important limit for the development of visual sensitivity.

Aging↗

PubMed1989

Spatial and spatiotemporal contrast sensitivity of normal and glaucoma eyes.

The spatial contrast sensitivity (CS) to static patterns was tested in the central retina of 156 normal subjects. It showed a decrease above 50 years of age at all spatial frequencies tested which was slightly more pronounced in females than in males. The spatial CS was also studied in 32 glaucoma eyes: Small reductions were found only in the group below 50 but not in eyes of patients above 50. The spatiotemporal CS to phase-reversing patterns was tested in four retinal quadrants of 99 normal subjects. It showed no age dependence in males whereas in females it decreased significantly beyond 50 years at all spatial frequencies tested. The spatiotemporal CS was studied also in 21 glaucoma eyes: Strong losses were again noted only in patients below 50. Spatiotemporal CS losses and perimetric losses were also compared in the four quadrants: For both measures the severest losses were found in the lower nasal and the mildest in the upper temporal quadrant. The spatiotemporal CS test of the peripheral retina seems to be a more powerful tool in glaucoma research than the spatial CS test of the central retina; however, effects of age and gender have to be considered.

Adult↗

PubMed1989

Contrast sensitivity in macular degeneration and the relation to subjective visual impairment.

Contrast sensitivity was determined with electronic and computer equipment (Cadwell CTS 5000) and with optotype test charts (LH low contrast test) in 31 patients, aged 47-89, with macular degeneration, mostly of the age-related type. Values of maximal sensitivity and mean sensitivity in different spatial frequency bands were estimated. Visual acuity at distance and the magnification factor needed for reading were also determined. Each of these measures were correlated with a score obtained in a subjective evaluation of difficulties with visual discrimination and orientation. It was found that poor visual discrimination and orientation was better correlated with low contrast sensitivity than with low visual acuity. The outcome of the LH-test was a better predictor of orientation problems than the electronic test.

Aged↗

PubMed1989

Contrast sensitivity norms for the Mentor B-VAT II-SG video acuity tester.

The Mentor B-VAT II-SG video acuity tester is a high-resolution video system designed to present many of the targets used in standard vision examinations (Snellen optotypes, clock charts, etc.). The SG model also presents sinusoidal gratings at various spatial frequencies and contrasts, making it possible to measure contrast sensitivity functions (CSF's). Using this system, we measured CSF's in a group of 69 young observers with well corrected vision. Contrast sensitivity scores were obtained at each of five spatial frequencies. A total of 5710 trials was presented. The mean contrast sensitivity scores of our group agree well with norms of other available CSF measurement systems, provided that the low spatial frequency truncation effects of each system are taken into account. A random subset of the group was retested 1 month later; no significant differences were found, demonstrating the reliability of the measurements. The data of this study should aid the clinician in identifying visual disorders. The data may be used to determine quantitative deviations from the norms or as a rapid screening test.

Adult↗

PubMed1983

Spatial contrast sensitivity of monocularly deprived cats after removal of the non-deprived eye.

Spatial contrast sensitivity was behaviorally determined for two monocularly lid-sutured cats. The spatial contrast sensitivity function for the non-deprived eyes matched previously reported functions obtained from normally reared cats. In comparison, sensitivity was significantly lower at all spatial frequencies for the deprived eye of both cats. In one cat, subsequent removal of the non-deprived eye resulted in a two to threefold increase in sensitivity at all spatial frequencies. However, no improvement in sensitivity was observed for the second animal. Single-unit electrophysiological recording in the striate cortex of these two animals revealed a postenucleation difference in the percent of visually influenced cells. In the cat for which no behavioral improvement occurred, only 13% of striate cortex cells could be driven by visual stimulation of the previously deprived eye. In contrast 38% of striate cortex cells were similarly influenced in the cat for which visual improvement was observed. These data suggest a correlation between the physiological effectiveness of the postcritical period enucleation procedure and the visual capacity of monocularly lid-sutured cats.

Amblyopia↗

PubMed1992

Evaluation of the efficacy of contrast sensitivity measures for the detection of early primary open-angle glaucoma.

We investigated the relative efficacy of contrast sensitivity (CS) measures for the identification of early primary open-angle glaucoma (POAG) patients. The contrast sensitivity function (CSF) was sampled at five spatial frequencies using a standard oscilloscope technique and measures of CS were also obtained using the Cambridge Gratings, Pelli-Robson CS Charts, Melbourne Edge Test (MET), and the High and Low Contrast Bailey-Lovie Letter Charts. Of the techniques evaluated, the High and Low Contrast Bailey-Lovie Letter Charts and the oscilloscope technique at the peak of the CSF exhibited the highest levels of sensitivity and specificity for differentiating between the POAG patients and normals. However, the relatively low levels of sensitivity and specificity obtained for the oscilloscope and chart tests overall indicate that, regardless of the pass/fail criterion selected, CS is unsuitable for screening for early POAG.

Adult↗

PubMed1990

Effects of dioptric blur on the Vistech contrast sensitivity test.

We studied the effect of dioptric blur on contrast sensitivity using the Vistech Vision Contrast System Chart. One diopter of blur affected the Vistech gratings by an amount consistent with expectations; sensitivity loss was greatest with higher spatial frequencies. However, a second diopter of blur induced an equal sensitivity loss for all spatial frequencies. A third diopter induced the greatest loss at the lowest frequency and an actual increase in sensitivity at the highest frequencies. This surprising finding is due to an interaction between "spuriously resolved" gratings and the border of the grating disc which resulted in the finest grating discs appearing to contain low frequency borders aligned with the fine gratings. Actually the fine gratings in the disc were invisible. When performing scanning photometry on the Vistech chart, we found that the contrasts of the unblurred gratings with higher contrast levels are 2.7 to 5.4 times higher than those stated by the manufacturer. The presence of this aliasing artifact indicates that the Vistech Vision Contrast System may produce erroneous results when used under conditions of high dioptric blur.

Adult↗

PubMed1998

Effects of a low concentration of isoflurane on contrast sensitivity in volunteers.

The effects of 0.15% quasi steady-state end-tidal isoflurane on the contrast sensitivity of five healthy volunteers were investigated by measuring their performance in computer generated letter discrimination tasks. A series of letters were displayed on a computer screen so that the luminance of the letter differed from that of the background. Two protocols were used: in the static protocol, the letter remained displayed on the screen until the subject responded, whereas in the dynamic protocol, the letter was displayed for 1/72 s only. Isoflurane significantly decreased contrast sensitivity in both protocols in all subjects.

Anesthesia Recovery Period↗

PubMed1968

The contrast sensitivity of the colour mechanisms of the human eye.

1. To isolate the colour receptive systems of the eye, a sinusoidal grating of one colour was superimposed on a bright background of another colour and the threshold contrast for resolving the grating was determined.2. A procedure is described which allows one to estimate the extent by which the bright background reduces the contrast of the test grating of another colour. Using this procedure, the measured threshold contrasts of the test grating were replotted in terms of the effective contrast sensitivity for the composite target.3. The effectivity of a red background in reducing the contrast of a green grating was found to be determined not by its apparent brightness but rather by the extent to which it excited the green mechanism.4. The effective contrast sensitivities for a green grating on a green background, for a green grating on a red background, and for a red grating on a green background were found to be not significantly different.5. Visual acuity for a blue grating on a yellow background was reduced from normal by about a factor of six. This loss in visual acuity was due to both a reduction in contrast sensitivity and a reduction in resolution.

Color Perception↗

PubMed1981

[Visual evoked potentials, contrast sensitivity and color perception in patients with optic nerve neuritis and multiple sclerosis].

Forty-nine patients with acute optic neuritis (in 21 cases associated with MS) and 26 patients known to have MS but with no history of optic nerve disease underwent visual evoked potential, contrast sensitivity and color vision tests. In patients with optic neuritis the contrast sensitivity was shown to detect optic nerve lesions better than the VEP an often permitted a distinction between acute and past optic neuritis. Combined testing with contrast sensitivity and VEP was superior to the single tests and detected 100% of the acute optic nerve lesions, although in many cases damage was selective and only involved some of the information channels. Desaturated color tests were abnormal in 3/4 of the patients, disturbances of blue-yellow discrimination being commoner than those of red-green. In cases with clinically unilateral optic neuritis the apparently normal partner eye was affected in 61% of the patients; complete recovery of optic nerve function without some residual deficit is rare. Approximately 3/4 of the eyes of patients known to have MS but with no history of past visual disturbances showed bilateral optic nerve involvement. The frequency of subclinical optic nerve lesions rose to 91% at a follow-up examination one year later. the literature is reviewed and our results are compared with the previously published data.

Adolescent↗

PubMed2006

Directional motion contrast sensitivity in developmental dyslexia.

The present study compared the perception of visual motion in two dyslexia classification schemes; the [Boder, E. (1973). Developmental dyslexia: a diagnostic approach based on three atypical reading-spelling patterns. Developmental Medicine and Child Neurology, 15, 663-687.] dyseidetic, dysphonetic and mixed subgroups and [Williams, M. J., Stuart, G. W., Castles, A., & McAnally, K. I. (2003). Contrast sensitivity in subgroups of developmental dyslexia. Vision Research, 43, 467-477.] surface, phonological and mixed subgroups by measuring the contrast sensitivity for drifting gratings at three spatial frequencies (1.0, 4.0, and 8.0 c/deg) and five drift velocities (0.75, 3.0, 6.0, 12.0, and 18.0 cyc/s) in a sample of 32 children with dyslexia and 32 matched normal readers. The findings show that there were no differences in motion direction perception between normal readers and the group with dyslexia when dyslexia was taken as a homogeneous group. Motion direction perception was found to be intact in the dyseidetic and surface dyslexia subgroups and significantly lowered in both mixed dyslexia subgroups. The one inconsistency in the findings was that motion direction perception was significantly lowered in the [Boder, E. (1973). Developmental dyslexia: a diagnostic approach based on three atypical reading-spelling patterns. Developmental Medicine and Child Neurology, 15, 663-687.] dysphonetic subgroup and intact in the [Williams, M. J., Stuart, G. W., Castles, A., & McAnally, K. I. (2003). Contrast sensitivity in subgroups of developmental dyslexia. Vision Research, 43, 467-477.] phonological subgroup. The findings also provide evidence for the presence of a disorder in sequential and temporal order processing that appears to reflect a difficulty in retaining sequences of non-meaningful auditory and visual stimuli in short-term working memory in children with dyslexia.

Adolescent↗

PubMed1984

Contrast sensitivity and visual disability in chronic simple glaucoma.

A battery of vision tests was used to quantify visual defect in a group of 50 patients with chronic simple glaucoma. The vision tests were near and distance visual acuity, visual fields, and contrast sensitivity to static and temporally modulated sinusoidal grating patterns. Of these, static contrast sensitivity function appears to be the most sensitive method of measuring visual defect in glaucoma patients. The visual disability experienced by the glaucoma patients was quantified by means of a questionnaire, and the relationship between perceived visual disability and visual defect was examined. It was found that results from a group of tests, near visual acuity, visual field, and contrast sensitivity measures, are the best predictors of the difficulty experienced by patients in performing visually dependent daily activities.

Activities of Daily Living↗

PubMed1980

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.

Animals↗

PubMed1986

Effect of Fresnel prism dispersion on contrast sensitivity function.

Fresnel prisms are often used in orthoptics for binocular anomalies and in low vision for visual field defects. These prisms are made of optical polyvinyl chloride (PVC) and this material increases chromatic dispersion and produces a loss of contrast. In this study, the effect of chromatic dispersion on contrast sensitivity is determined. Contrast thresholds over a wide range of spatial frequencies are obtained on a number of subjects with the use of Fresnel prisms ranging from 5 to 30 prism dioptres. As predicted there is a decrease in visual acuity and cut-off spatial frequency threshold as prism power increases. Similarly, a decrease in contrast sensitivity at high and medium spatial frequencies is recorded.

Form Perception↗

PubMed1984

An analysis of contrast sensitivity in identical twins with keratoconus.

We studied a pair of 36-year-old identical twins with keratoconus, one of whom had undergone bilateral penetrating keratoplasties. Both patients had final best corrected Snellen visual acuity of approximately 20/20. However, contrast sensitivity functions for the unoperated twin were abnormal when compared to the operated twin. In addition, contrast sensitivity data for the operated twin during and after a graft rejection indicate that corneal graft opacity and distortion can significantly alter the contrast sensitivity function. The unusual occurrence of identical twins with keratoconus afforded the unique opportunity to explore the visual and psychophysical aspects of keratoconus in a genetically controlled setting.

Adult↗

PubMed2002

Interactions between chromatic- and luminance-contrast-sensitive stereopsis mechanisms.

It is well known that chromatic information can assist in solving the stereo correspondence problem. It has also been suggested that there are two independent first-order stereopsis mechanisms, one sensitive to chromatic contrast and the other sensitive to luminance contrast (Vision Research 37 (1997) 1271). Could the effect of chromatic information on stereo correspondence be subserved by interactions between these mechanisms? To address this question, disparity thresholds (1/stereoacuity) were measured using 0.5 cpd Gabor patches. The stimuli possessed different relative amounts of chromatic and luminance contrast which could be correlated or anti-correlated between the eyes. Stereoscopic performance with these compound stimuli was compared to that with purely isoluminant and isochromatic stimuli at different contrasts. It was found that anti-correlated chromatic contrast severely disrupted stereopsis with achromatic stimuli and that anti-correlated luminance contrast severely disrupted stereopsis with chromatic stimuli. Less dramatic, but still significant, was the improvement in stereoacuity obtained using correlated colour and luminance contrast. These data are consistent with there being positive and negative interactions between chromatic and achromatic stereopsis mechanisms that take place after the initial encoding of disparity information, but before the extraction of stereoscopic depth. These interactions can be modelled satisfactorily assuming probability summation of depth sign information between independent mechanisms.

Color Perception↗