Contrast (vision)

About: Contrast (vision) is a research topic. Over the lifetime, 10379 publications have been published within this topic receiving 221480 citations.

Contrast sensitivity in age-related macular degeneration.

Abstract: • Low-contrast charts were used to investigate the possibility that patients with drusen have visual deficits not detected by standard Snellen charts. We compared performance on Regan letter charts between 52 eyes with drusen and Snellen acuity of 20/20 and 27 control eyes. The drusen group read fewer letters than the control group on all of the charts tested. This difference increased as the contrast of the charts decreased. The loss of performance on all of the Regan charts correlated with drusen severity. Twenty-one eyes with drusen and normal Snellen acuity also were tested with a Ginsburg contrast sensitivity chart and compared with age-matched normal controls. The results showed a loss of contrast sensitivity at high spatial frequencies and a loss of peak contrast sensitivity with increasing drusen severity. These results suggest that in patients with drusen, low-contrast charts may be useful for measuring visual loss not detected by standard Snellen charts.

Subjective depth-of-focus of the eye.

Abstract: An experiment is described in which the subjective depth-of-focus (DOF) of the eye, defined as the range of focusing errors for which the image of the target appears to have the same clarity, contrast, and form as the optimal in-focus image, was measured as a function of the size of high contrast (99%) Snellen Es for 5 trained subjects under cycloplegia. Mean DOF increased by approximately 60% as the size of the letter detail increased from -0.2 to 0.87 log min arc (Snellen equivalent: 6/3.8 to 6/45), although there were considerable intersubject variations. DOF declined with increasing pupil diameter, the mean total DOFs being 0.86, 0.59, and 0.55 D for 2-, 4-, and 6-mm pupils, respectively. In a second experiment, use of low (21%) contrast letters with a 4-mm pupil and 4 subjects marginally increased the DOF (by 0.08 +/- 0.05 D); refraction also shifted in a myopic direction by a mean of 0.15 +/- 0.06 D compared with the high contrast letters. A third experiment with four less-experienced subjects demonstrated the importance of instruction and training in any measurement involving judgment of just-perceptible defocus blur. The clinical implications of the results for measurements of refraction and amplitude of accommodation are discussed.

Lack of cortical contrast gain control in human photosensitive epilepsy

Abstract: Television and video games may be powerful triggers for visually induced epileptic seizures. To better understand the triggering elements of visual stimuli and cortical mechanisms of hyperexcitability, we examined eleven patients with idiopathic photosensitive epilepsy by recording visually evoked potentials (VEPs) in response to temporally modulated patterns of different contrast. For stimuli of low–medium, but not high, temporal frequency, the contrast dependence of VEP amplitude and latency is remarkably abnormal for luminance contrast (black–white), but not so for chromatic contrast (equiluminant red–green) stimuli. We conclude that cortical mechanisms of contrast gain control for pattern stimuli of relatively low temporal frequency and high luminance contrast are lacking or severely impaired in photosensitive subjects.

Measuring contrast sensitivity in normal subjects with OPTEC® 6500: influence of age and glare

Abstract: The purpose of this study was to develop age-related curves for contrast sensitivity (CS) in normal subjects under day and night conditions with and without glare. Sixty-one healthy eyes from 61 subjects were measured with the OPTEC® 6500 P under day and night conditions (luminance levels: 85 cd/m2 and 3.0 cd/m2 with and without glare; spatial frequencies: 1.5, 3, 6, 12 and 18 cycles/degree). A reliability analysis with five repeated measurements of six persons on 4 days was performed to examine the repeatability. The influence of age on contrast sensitivity, forward and backward scatter was examined by means of linear regression. Contrast sensitivity was significantly reduced under night conditions with glare, whereas glare had less influence under daylight illumination. Mean reliability coefficients are 0.87 (day), 0.77 (day with glare), 0.69 (night) and 0.81 (night with glare), which suggests sufficient retest reliability of the device. Regression analyses showed a highly significant influence of age, but the variance of the measurement values is not explained by age alone. The coefficients of determination for the regression of area under the log contrast sensitivity function (AULCSF) on age are 0.33 (photopic), 0.34 (photopic with glare), 0.29 (mesopic) and 0.36 (mesopic with glare, p < 0.0001 in all cases). A significant relationship between age, CS and scatter was confirmed in our study. The results provide baseline values for the examination of patients with different diseases in which contrast sensitivity is impaired (such as glaucoma, cataracts and amblyopia) and might be useful in studies of roadworthiness or in investigation of the impact of intraocular lenses.

New look at Bloch's law for contrast.

Abstract: It has been commonly reported that the temporal integration of grating contrast proceeds more slowly as spatial frequency is increased. Such results have been based on the critical duration for sensitivity to contrast pulses varying in duration, but the analyses have not assumed full integration at short durations and have neglected the effects of probability summation over time. To take such effects into account, we discuss a class of analytical models based on nonlinear temporal integration. On the assumption that the temporal impulse response of the visual system determines contrast integration over time, we develop both a high-threshold model and a signal-detection approach involving multiple and independent nonlinear signal detectors with a time-limited integration span. The redefined critical durations predicted by the models and verified by the data are about 35 msec and vary by no more than 10 msec across spatial frequency. This variation is entirely attributable to a change in the strength of inhibition with spatial frequency, and the analysis implies that the excitatory component is constant at all spatial frequencies, contrary to previous accounts.