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PubMed1993

Effect of color on contrast sensitivity with two different accommodative stimuli.

We studied the influence of color and accommodation on the contrast sensitivity function (CSF). At the same time, we measured the effect of axial chromatic aberration (ACA) on the CSF. The CSF's of two observers were determined using red, green, blue, and white light, at 5- and 0.5-m viewing distances. At 5 m the CSF's were measured with natural vision and also with lenses which compensated the ACA. Results show that the effect of ACA on the CSF is to reduce the sensitivity to blue with respect to the red. The difference in sensitivity between these two colors is between 50 and 150% and varies with the frequency and the subject. When the ACA is compensated the influence of the color on the CSF is very small, in our experiment, and this result is discussed in relation to the compensating effects of chromatic adaptation of the color mechanisms. In near vision, the CSF's were measured with natural vision and also with the lenses required to give the same accommodative stimulus for all colors. We discuss the effect of accommodation on the CSF. For both far and near the results are compared with the CSF with white light.

Accommodation, Ocular↗
PubMed1988

The effects of ingestion of 60 mg pyridostigmine bromide on contrast sensitivity in man.

The effects on vision of ingestion of the anticholinesterase pyridostigmine bromide (60 mg), assessed from pharmacokinetic data to provide at least 20% inhibition of blood cholinesterase over the 1 1/2-4 1/2 h experimental period, was compared with 60 mg lactose in a double-blind crossover protocol. Contrast sensitivity to stationary oscilloscope-generated gratings of 3-40 c/deg showed a small but significant increase of 7% which was consistent with a small reduction in pupil diameter, surmised to cause a small improvement in optical quality. This reduction in pupil diameter was, however, overshadowed by a larger though still non-significant reduction on the second visit to the laboratory compared with the first. Contrast sensitivities to laser interference fringes observed in the Maxwellian view, by which the effects of the optical media are essentially bypassed, thus providing an entirely neural assessment, were unchanged after pyridostigmine. It is concluded that pyridostigmine may be given as a prophylactic in anticipation of exposure to an organophosphorus anticholinesterase without a deleterious effect on stationary visual function.

Adult↗
PubMed1979

Abnormalities of central contrast sensitivity in glaucoma.

The detectability of foveally presented low-contrast flickering stimuli was determined for glaucoma patients, ocular hypertensives, and normal control subjects. Two types of stimuli, a homogeneous flickering field, and a counterphase flickering grating of low spatial frequency, were presented on a screen subtending 4 degrees of visual angle. The average of the contrast sensitivities to these two simuli (defined as the dynamic response coefficient) was consistently lower in glaucomatous than in normotensive eyes. The dynamic response coefficient was also below normal in half the ocular hypertensive eyes.

Adult↗
PubMed1987

The effect of optical degradation on the contrast sensitivity function measured at the fovea and in the periphery.

Contrast sensitivity functions (CSF's) were measured for a zone of 0.5 degree angular radius at the fovea and for annular zones extending from 0.5 degrees eccentricity to 1 degree, from 1 to 2 degrees and from 2 to 4 degrees. The effect of optical degradation was taken into account by the application of a correction factor determined from the Modulation Transfer Function (MTF). Using the reciprocal of the peak of the CSF [1/SF (max)] as a parameter, the effect of applying the MTF correction on the CSF with eccentricity was determined. The effect of applying an MTF correction is significantly to increase the rate of change of 1/SF (max) with eccentricity. Since it has been reported that hyperacuity is relatively unaffected by optical degradation, it is proposed that the differing effects of optical degradation between grating acuity and hyperacuity may account, at least partially, for the different rates of decline of these thresholds with eccentricity. The implications of this proposal for M-scaling theories and strategies are considered.

Fovea Centralis↗
PubMed2005

Senescence of spatial chromatic contrast sensitivity. I. Detection under conditions controlling for optical factors.

Chromatic contrast thresholds for spatially varying patterns of various spatial frequencies (0.5, 1, 2, and 4 cycles per degree) were measured for ten older (65-77 yr of age) and ten younger (18-30 yr of age) observers. The stimuli were Gabor patches modulated along S-varying or (L - M)-varying chromatic axes. Thresholds were determined for two sets of stimuli. For one set of stimuli, the mean chromaticity and luminance were equated at the cornea for all observers. The second set of stimuli was corrected for ocular media density differences to equate stimulation of each of the three cone types at the retina for each individual. Chromatic contrast thresholds were higher for older observers for all stimuli tested. The magnitude of this difference showed little dependence on spatial frequency. When stimuli were equated at the cornea, this difference was greater for S-varying stimuli. When stimuli were equated at the retina, the age-related difference in thresholds for S-varying stimuli was reduced. Both optical and neural factors contribute to these age-related losses in spatial chromatic contrast sensitivity.

Adolescent↗
PubMed1981

Contrast sensitivity and retinal disease.

A new and practical test for contrast sensitivity (Arden gratings) was evaluated in retinal diseases and found to be a more sensitive indicator of dysfunction than Snellen acuity. Most patients with acuity of 20/30 or better (e.g., with retinitis pigmentosa or toxic retinopathy) showed diminished sensitivity to finely spaced gratings, while patients with poor acuity (e.g., with cone dystrophy) showed normal sensitivity to coarsely spaced gratings. Grating tests may allow earlier diagnosis and more precise follow-up of retinal disease, but their specificity for particular disorders remains to be established.

Adult↗
PubMed1987

Investigation of contrast sensitivity following radial keratotomy.

Radial keratotomy is a surgical procedure for the correction of myopia in which the cornea is flattened by partial-thickness radial incisions. While postoperative visual acuity is usually good, measurements of acuity are of only limited value and do not describe visual performance for a variety of spatial frequencies and contrasts. In the present study, the effect of radial keratotomy on the contrast-sensitivity function was examined. Six spatial frequencies were tested (0.5, 1.0, 3.0, 6.0, 11.4, and 22.8 cycles/degree) using the Nicolet CS 2000 with patients wearing corrective lenses. The results revealed that, at least for the conditions tested, radial keratotomy does not produce a statistically significant decline in contrast sensitivity.

Humans↗
PubMed1996

[Reproducibility of contrast sensitivity test results].

Two methods (a double staircase and an adjustment method) for repeated measuring of the contrast sensitivity in inexperienced observers (e.g. in patients undergoing the photorefractive keratectomy) were compared in 10 subjects. Using the coefficient of repeatability of Bland and Altmann it could be shown that the reproducibility is better in the method of adjustment. The coefficient of repeatability of this method amounted for 95% confidence limits to 4.78 dB, whereas in the method of double staircase it was 8.70 dB.

Adult↗
PubMed1984

Effects of strabismus on responsivity, spatial resolution, and contrast sensitivity of cat lateral geniculate neurons.

Rearing cats with esotropia is known to cause a number of deficits in visual behavior tested through the deviated eye. These include a loss of orienting response to stimuli presented in the nasal visual field of the deviated eye, a reduction in visual acuity, and a general reduction in contrast sensitivity at all spatial frequencies. To assess the involvement of the lateral geniculate nucleus (LGN) in these deficits, we measured the following: 1) the visual responsiveness of lamina A1 cells with peripheral (more than 10 degrees from area centralis) receptive fields in three esotropic and three normal cats and 2) the spatial resolution and contrast sensitivity of lamina A X-cells with central (within 5 degrees of the area centralis) receptive fields in six esotropic and six normal cats. For comparison, we also measured LGN X-cell spatial resolutions in four exotropic cats and in two cats raised with an esotropia in one eye and the lids of the other eye sutured shut (MD-estropes). Recordings from the lateral portion of lamina A1 in esotropic cats yielded similar numbers of visually responsive cells with far nasal receptive fields as were seen in normal animals. Peak and mean response rates to a flashing spot also were normal. In addition, no differences were found between esotropes and normals in the percentages of X- and Y-cells encountered. These results suggest that the loss of orienting response to stimuli presented in the nasal field (12, 20) is not due to a loss of neural responses in the LGN of esotropic cats. In addition, they suggest that decreases in cell size in lamina A1 of esotropic cats (13, 36; R. E. Kalil, unpublished observations) are not accompanied by marked functional abnormalities of the cells and that cortical abnormalities ipsilateral to the deviated eye (22) are likely to have their origin within striate cortex itself. Recordings from lamina A cells with receptive fields near area centralis revealed that the average X-cell spatial resolution in esotropes (2.1 cycles/deg) was significantly lower than that in normal cats (3.1 cycles/deg). This reduction was seen in all esotropic cats tested and was due both to an increase in the proportion of X-cells with very low spatial resolution and to a loss of X-cells responding to high spatial frequencies (greater than 3.25 cycles/deg). The average spatial resolution of X-cells driven by the deviated eye in MD-esotropes fell midway between those of esotropes and normals. In exotropes, mean X-cell spatial resolution was normal.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed2006

Intermediate spatial frequency letter contrast sensitivity: its relation to visual resolution before and during amblyopia treatment.

We examined the loss of letter contrast sensitivity (LCS) measured using the Pelli-Robson chart, and the extent to which any such loss was modulated by spectacle wear and occlusion therapy in children participating in an amblyopia treatment trial. Their initial mean interocular difference in logMAR acuity was approximately three times that of their LCS (0.45 vs 0.14 log units). Log LCS was weakly though significantly correlated with logMAR visual acuity (VA) for all VAs better than 0.90 (r = -0.19, 95% CI: -0.28 to -0.10) whereas for all VAs of 0.90 or poorer, log LCS was markedly and significantly correlated with VA (r = -0.72, 95% CI: -0.83 to -0.53). LCS in those children with a > or =0.1 log unit interocular difference on this test improved commensurately with VA during treatment. We conjecture that the spatial visual loss in all but the most severe amblyopes occurs in an area of resolution and contrast space that lies beyond that sampled by the Pelli-Robson chart.

Adaptation, Physiological↗
PubMed2005

Oxygen-sensitive contrast in blood for steady-state free precession imaging.

Steady-state free precession (SSFP) methods have gained widespread recognition for their ability to provide fast scans at high signal-to-noise ratio. This paper demonstrates that such methods are also capable of reflecting functional information, particularly blood oxygenation state. It is well known that SSFP signals show substantial sensitivity to small off-resonance frequency variations. However, that mechanism cannot explain the oxygen-sensitive contrast in blood that was observed with steady-state methods using phase-cycled radiofrequency pulses. From theoretical and experimental models it is demonstrated that the mechanism responsible for such contrast originates from the motion of spins through local field inhomogeneities in and around deoxygenated red blood cells. In addition, this work shows that it is critical to choose the scan parameters carefully for robust oxygen-sensitive contrast. Finally, it is demonstrated that it is possible to build a quantitative model that incorporates the Luz-Meiboom model, which had been used in the past to estimate quantitative measures of vascular blood oxygen levels. It is envisioned that this method could be instrumental in real-time imaging focused on detecting diseases where the oxygen state of blood is impaired.

Chi-Square Distribution↗
PubMed1993

Spatiotemporal contrast sensitivity of early vision.

Based on the spatial and temporal statistics of natural images, a theory is developed that specifies spatiotemporal filters that maximize the flow of information through noisy channels of limited dynamic range. Sensitivities resulting from these spatiotemporal filters are very similar to the human spatiotemporal contrast sensitivity, including the dependence on ambient light intensity. The theory predicts several psychophysical laws: Ferry-Porter's law, the de Vries-Rose law, Weber's law, Bloch's law, Ricco's law, and Piper's law.

Contrast Sensitivity↗
PubMed2006

Contrast sensitivity in 10 year old preterm and full term children: a population based study.

AIMS: To determine the contrast sensitivity (CS) in 10 year old prematurely born children, previously included in a population based study on the incidence of retinopathy of prematurity (ROP), and in full term controls. METHODS: This study included 205 prematurely born children and 215 children born at term, from the same geographical area and study period. CS was assessed monocularly with the Vistech 6500 test at five spatial frequencies (1.5-18 cycles/deg). RESULTS: Prematurely born children had statistically significant lower CS at all frequencies, compared to full term ones. The mean differences in logarithmic CS were 0.03 (1.5 cycles/deg), 0.09 (3 cycles/deg), 0.10 (6 cycles/deg), 0.12 (12 cycles/deg), and 0.19 (18 cycles/deg). Even when the children with ROP and neurological disorders were excluded there was a difference between the two groups. Children who had been treated with cryotherapy had the lowest CS. CONCLUSION: CS was lower in 10 year old prematurely born children than in full term ones of the same age. Whether this finding affects their visual function in daily life is uncertain.

Child↗
PubMed1998

Predicting the effects of optical defocus on human contrast sensitivity.

We used diffraction modulation transfer functions and model eyes to predict the effect of defocus on the contrast sensitivity function (CSF) and compared these predictions with previously published experimental data. Using the principle that optically induced changes in the modulation transfer function should be paralleled by identical changes in the CSF, we used the modulation transfer function calculations with the best-focus CSF measurements to predict the defocused CSF. An aberration-free model predicted the effects of defocus well when the CSF was measured with small pupils (e.g., 2 mm) but not with larger pupils (6-8 mm). When the model included average aberrations, prediction of the defocused CSF with large pupils was better but remained inaccurate, failing, in particular, to reflect differences between individual subjects. Inclusion of measured aberrations for individual subjects provided accurate predictions in the shape of the monochromatic CSF of two of three subjects with hyperopic defocus and good predictions of the polychromatic CSF of two subjects with hyperopic defocus. Prediction of the effects of myopic defocus by use of measured individual aberrations of one subject were less successful. Hence a diffraction optics model can provide good predictions of the effects of defocus on the human CSF, given that one has knowledge of the individual ocular aberrations. These predictions are dependent on the quality of the aberration measurements.

Contrast Sensitivity↗
PubMed2000

Iodinated contrast sensitivity in ERCP.

Iodine contrast media are detectable in the bloodstream after ERCP, and sensitivity reactions have been described. The risk is very small, and the phenomenon is therefore difficult to study. This review discusses the possible need for preventative strategies, and recommends that endoscopists consider the issue and define their own policies.

Cholangiopancreatography, Endoscopic Retrograde↗
PubMed1988

Effects of temporal frequency on the contrast sensitivity of the human accommodation system.

Contrast thresholds were determined for the initiation of accommodative responses to drifting sine-wave stimuli (4.1 c/deg) over a range of temporal frequencies (0-14.0 Hz). Accommodation was monitored with a dynamic infrared optometer. Psychophysical detection thresholds were also determined for the same stimuli. A comparison of the contrast thresholds for detection with those for the initiation of accommodation indicates that these two tasks are mediated by mechanisms of comparable sensitivity. Examination of the effects of temporal frequency on the contrast sensitivity of these two visual tasks reveals modest differences in the tuning properties of the underlying sensory mechanisms. Transient mechanisms tuned to intermediate temporal frequencies appear to have a greater role in the initiation of accommodative responses to grating stimuli than in the detection of such stimuli.

Accommodation, Ocular↗
PubMed1988

Reliabilities of alternate measures of contrast sensitivity functions.

In four studies, the comparability of several measures of contrast sensitivity functions (CSF's) as well as their individual test-retest reliabilities were determined with observers drawn from a college population. The relation between CSF scores obtained by different tests or by different psychophysical procedures with the same test was consistently low and frequently nonexistent. These low intertest reliabilities were found to be due to the lack of reliability of some of the individual tests. In particular, with both stationary and flickering gratings, the von Bekesy tracking procedure produced unacceptable variations in contrast estimates. Fortunately, the reliabilities of other procedures, particularly the simple adjustment method, were much higher (greater than 0.70). CSF scores obtained from the wallchart method exhibited insufficient variability among observers in the college sample to permit similar reliability estimates to be determined. Implications of the test characteristics are discussed for users of the CSF.

Adult↗