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PubMed1998

Contrast sensitivity loss in the neglected hemifield.

Contrast sensitivity to gratings of various spatial frequencies displayed in the left and right visual hemifield was measured in a group of ten right brain-damaged patients with unilateral visuospatial neglect. Two groups of ten left brain-damaged (LBD) and ten right brain-damaged (RBD) patients without neglect served as controls. All patients had normal visual fields according to standard clinical procedure. Stimuli were patches of sinusoidal gratings of 1, 2, 4 and 8 c/deg spatial frequency. The patches subtended 6 deg and were displayed at 3 deg of eccentricity. A two-alternative forced-choice technique was employed. Results showed a reduction in contrast sensitivity for stimuli presented to the contralesional hemifield with respect to the ipsilesional hemifield in patients with neglect. No difference in contrast sensitivity between hemifields was found for LBD and RBD groups. These findings indicate a basic visual impairment in the contralesional hemifield in patients with neglect.

Aged↗
PubMed2001

The effect of orientation learning on contrast sensitivity.

Regan and Beverley [Regan, D., & Beverley, K. I. (1985). Postadaptation orientation discrimination. Journal of the Optical Society of America A, 2(2), 147-155] previously demonstrated that adapting to an oriented visual stimulus improves sensitivity to subtle orientation differences while impairing contrast sensitivity. Here, we investigated whether practice-based improvements in orientation sensitivity would, like adaptation, impair contrast sensitivity. To the contrary, we found that contrast sensitivity actually improved significantly after observers demonstrated practice-based increases in orientation sensitivity. Therefore, while orientation sensitivity can be enhanced either by orientation-discrimination training or by adapting to visual stimuli, these two procedures have opposite effects on contrast sensitivity. This difference suggests that adaptation and perceptual learning on orientation discrimination cannot be explained sufficiently by a shared underlying cause, such as a reduction in neural activity.

Adaptation, Physiological↗
PubMed1995

Modelling the increase of contrast sensitivity with grating area and exposure time.

We extended the contrast detection model of human vision to temporal integration by taking into account the effect of exposure duration on contrast sensitivity for stationary gratings. The extended model thus comprised: (i) low-pass filtering due to the optical modulation transfer function of the eye; (ii) high-pass filtering (lateral inhibition) due to the neural modulation transfer function of the visual pathways; (iii) addition of internal neural noise; and (iv) detection by a local matched filter whose efficiency for gratings decreased with increasing area and exposure duration. To test the model we measured binocular contrast sensitivity in foveal photopic vision as a function of exposure duration and area for sinusoidal gratings with equiluminous surround at spatial frequencies of 0.25-16 c/deg. In agreement with the model, contrast sensitivity at all grating areas first increased in proportion to square root of t when exposure duration (t) was shorter than critical duration. Thereafter the increase saturated and contrast sensitivity became independent of exposure time. Critical exposure duration was found to be independent of grating area but increased with spatial frequency. Similarly, at all exposure durations contrast sensitivity first increased in proportion to square root of A when grating area (A) was smaller than critical area. Thereafter the increase saturated and contrast sensitivity became independent of area. Critical area was found to be independent of exposure duration but decreased with increasing spatial frequency. The extended model explained 95-97% of the total variance of our contrast sensitivity data at the spatial frequencies studied. Our results also mean that spatial and temporal integration processes are mutually independent and thus area and time are separable variables in the detection of stationary gratings.

Adult↗
PubMed1991

Contrast sensitivity changes in background diabetic retinopathy.

Previous reports of contrast sensitivity in diabetic patients have shown conflicting results. We evaluated contrast sensitivity using Cambridge low-contrast sensitivity charts in 22 diabetic patients (22 eyes without retinopathy and 16 eyes with background retinopathy on fluorescein angiography) and 10 control subjects (20 eyes) matched for age and sex. The mean contrast threshold values at a spatial frequency of 4 cycles/degree were 0.46%, 0.60% and 0.43% in the three groups of eyes respectively. Contrast sensitivity was significantly lower in the diabetic eyes with retinopathy than in the normal eyes (p = 0.011) or the diabetic eyes without retinopathy (p = 0.033). This test may be of value in screening diabetic patients for retinopathy in primary care facilities.

Contrast Sensitivity↗
PubMed2000

Colour contrast sensitivity in cataract and pseudophakia.

PURPOSE: To study the influence of cataract on peripheral and central colour contrast sensitivity. METHODS: Peripheral and central colour contrast sensitivity was measured with a computer graphics system along the protan, deutan and tritan axes. Included were 30 patients with cataract divided into three sub-groups: cortical cataract, nuclear sclerosis and posterior subcapsular cataract. Colour contrast was measured before and after cataract operation. RESULTS: There were significant differences in peripheral colour contrast thresholds comparing the preoperative and postoperative results. This difference existed even in patients (n=19) with a pre-operative visual acuity > or = 0.5 (mean 0.6). The tritan axis was the one most affected by cataract. There was no significant difference between cataract sub-groups. Also, the central colour contrast sensitivity was affected by cataract. Again, the tritan axis was the most affected one. There was no significant difference between the cataract sub-groups. We also found large and significant differences in central colour contrast thresholds between normal subjects and postoperative values from the cataract group in all colour axes. The colour contrast sensitivity was poorer in pseudophakes than in normals. There was a difference between the three groups of different IOL material used (PMMA, acrylic and silicone). The difference was significant in the protan axis, the acrylic group having the best colour contrast sensitivity. CONCLUSION: Peripheral colour contrast sensitivity was affected by cataract, even when only moderately developed. This finding is of importance and should be considered when the method is used to study other eye diseases e.g. glaucoma. Central colour contrast sensitivity was also affected by cataract. The pseudophakes were found to have poorer colour contrast sensitivity than normals. The material in the IOL seemed to be of importance for colour contrast.

Acrylates↗
PubMed1984

Temporal integration and contrast sensitivity in foveal and peripheral vision.

Spatial contrast sensitivity functions and temporal integration functions for gratings with dark surrounds were measured at various eccentricities in photopic vision. Contrast sensitivity decreased with increasing eccentricity at all exposure durations and spatial frequencies tested. The decrease was faster at high than at low spatial frequencies, but similar at different exposure durations. When cortically similar stimulus conditions were produced at different eccentricities by M-scaling, contrast sensitivity became independent of visual field location at all exposure durations tested. The results support the view that in photopic vision spatiotemporal information processing is qualitatively similar across the visual field, and that quantitative differences result from retino-topical differences in ganglion cell sampling. For gratings of constant retinal area temporal integration (improvement of contrast sensitivity with increasing exposure duration) was more extensive at high than at low retinal spatial frequencies but independent of cortical spatial frequency and eccentricity. For M-scaled gratings temporal integration was more extensive at high than at low cortical spatial frequencies but independent of retinal spatial frequency and eccentricity. The results suggest that the primary determinant of temporal integration is not spatial frequency but grating value that is calculated as AF2 square cycles (cycle2), where A is grating area and F spatial frequency.

Fixation, Ocular↗
PubMed2003

[A new device for measuring contrast sensitivity with and without glare].

PURPOSE/METHOD: To measure the photopic contrast sensitivity, with and without glare, by means of a new instrument. Seventy eight right eyes of 49 young adults and of 29 adults subjects between 35 and 55 years were studied. Contrast sensitivity was measured with the Contrast Glaretester CGT-1000 (Takagi, Japan) that determines the contrast threshold by means of an automated strategy for 6 spatial frecuencies. RESULTS/CONCLUSIONS: The values of contrast sensitivity were similar to those obtained with other clinical tests. Contrast sensitivity, without and with glare, decreased significantly with the age. However, glare did not modify the contrast sensitivity under photopic conditions.

Adolescent↗
PubMed1998

Contrast sensitivity after laser in situ keratomileusis.

PURPOSE: To evaluate the effect on contrast sensitivity function of laser in situ keratomileusis (LASIK) for the correction of myopia. SETTING: Alicante Institute of Ophthalmology, University of Alicante, Spain. METHODS: Fourteen eyes of 10 patients had LASIK to correct myopia ranging from 6.00 to 19.50 diopters (D). Mean preoperative myopia was 10.39 D +/- 3.69 (SD). Contrast sensitivity was tested preoperatively and 1, 3, and 6 months postoperatively using the CVS-1000E contrast sensitivity unit (VectorVision). RESULTS: Contrast sensitivity decreased 1 month postoperatively; the decrease was significant only at the low and intermediate spatial frequencies of 3 and 6 cycles per degree (cpd) (P = .034 and .030, respectively). Starting from the first month, there was rapid recovery of contrast sensitivity and at the third month, no statistically significant decrease at all spatial frequencies. Six months after surgery, there was an increase in contrast sensitivity values at 3, 12, and 18 cpd, although the changes were not significant. CONCLUSION: Although LASIK decreased contrast sensitivity values at low and intermediate spatial frequencies for 1 month after surgery, these values rapidly returned to the preoperative values at 3 months. The improvement at certain frequencies at 6 months suggests that LASIK can improve the quality of vision in eyes with moderate and high myopia.

Adult↗
PubMed1986

Contrast sensitivity in amblyopia. III. Effect of occlusion.

Contrast sensitivity of 26 children (mean age 9 years) was measured using vertical gratings during the course of pleoptic treatment. A statistically highly significant improvement in the vision of amblyopic eyes occurred during intensive treatment in the hospital. Occlusion of the amblyopic eye (inverse occlusion) before the pleoptic treatment did not effect the function of the amblyopic eyes. During 8-week occlusion of the dominant eye (direct occlusion) after pleoptic treatment changes in the vision of the amblyopic eyes were statistically insignificant. In some patients there was change in contrast sensitivity without a corresponding change in visual acuity. The contrast sensitivity of the dominant eye decreased markedly during occlusion in 12 patients. After a continuous occlusion of only 2 weeks there was a statistically significant decrease at spatial frequency 6 c/deg. There was no simultaneous decrease of visual acuity; thus the change can be called 'hidden occlusion amblyopia'. An additional 8-week occlusion did not cause any statistically significant decrease in contrast sensitivity, but visual acuity of 2 patients decreased slightly, a sign of beginning occlusion amblyopia. The changes disappeared during 'Einschleich'-occlusion or penalization except in one child whose previously dominant eye became non-dominant and slightly amblyopic.

Adolescent↗
PubMed1975

Contrast sensitivity in humans with abnormal visual experience.

1. Grating contrast sensitivities have been determined over a range of spatial frequencies for a normal subject and for subjects who are visually biased in that they have a lower resolution capacity for targets of specific orientations. The bias si only found in astigmatic subjects and the grating orientation yielding poorest acuity coincides with the most defocused astigmatic meridian. However this resolution anisotropy remains when optical factors are accounted for. 2. For the normal subject, high and low frequency attenuation is found and a typical reduction in contrast sensitivity is exhibited for oblique target orientations. 3. The biased subjects, called meridional amblyopes because they have reduced acuity for a given grating orientation, show markedly abnormal contrast sensitivity functions. Their cut-off spatial frequencies are different for various target orientations and this difference applies also to contrast sensitivity over nearly the entire spatial frequency range tested (0-5-16 cycles/deg). The differences are of about the same magnitude for most frequencies and they are found in all types of meridional amblyopes. 4. Optical explanations of these differences are ruled out by laser-interference fringe tests and by varying effective pupil size. 5. Theoretical effects of defocus have been calculated to compare predicted visual deprivation with performance. Results indicate that reduced contrast sensitivity functions can be equivalent to a small defocus effect. 6. To examine the results in the spatial domain, inverse Fourier transforms of representative contrast sensitivity functions have been computed. The optical portion of the resulting spatial weighting functions has been parcelled out to obtain neural spatial weighting functions.

Amblyopia↗
PubMed1993

Effects of luminance and exposure time on contrast sensitivity in spatial noise.

Using gratings with and without spatial noise we measured r.m.s. contrast sensitivity as a function of (i) retinal illuminance, (ii) amount of light added onto the screen, and (iii) exposure time. Our experiments showed that contrast sensitivity in external spatial noise was independent of decreasing retinal illuminance and exposure time as long as contrast sensitivity was lower with noise than without. Thereafter the decrease of contrast sensitivity was identical with and without noise. Although contrast sensitivity without external spatial noise was independent of the amount of added light, contrast sensitivity in external spatial noise was found to increase with the amount of added light until it reached the sensitivity measured without noise. Thereafter contrast sensitivities with and without noise were identical. Our results (i) provide experimental evidence for the validity of the generally accepted hypothesis that in the human contrast detection mechanism signal-to-noise ratio is constant at threshold and (ii) indicate that external spatial noise is the principal source of noise when it reduces contrast sensitivity.

Adult↗
PubMed2000

Contrast sensitivity function in patients with beta-thalassemia major.

PURPOSE: To investigate contrast sensitivity function in patients with beta-thalassemia major, after regular transfusion and chelation therapy. METHODS: We measured contrast sensitivity at four spatial frequencies in 30 patients with beta-thalassemia major and in 30 matched normal control subjects. All subjects underwent an ophthalmic examination that included fluorescein angiography. The contrast sensitivity results from the two groups were compared between them. Patients' contrast sensitivity values were correlated to the variables age, duration of transfusion, duration of chelation therapy and serum ferritin levels, to select the important predictors. RESULTS: Contrast sensitivity function in all beta-thalassemic patients was significantly lower (p<0.0001) compared to the normal control subjects, for all spatial frequencies tested. The most important predictor of contrast sensitivity loss was patients' age. CONCLUSION: Contrast sensitivity testing can detect early changes in the visual function of beta-thalassemic patients and should be considered as a monitor for patients under chronic transfusion-chelation therapy.

Adolescent↗
PubMed1988

Spatial contrast sensitivity in clinical neurology.

We studied contrast sensitivity function in normal subjects and in three illustrative cases with various neurological disorders. This was done by measuring contrast sensitivity over a range of spatial frequencies for vertical sinewave grating stimuli. It is demonstrated that contrast sensitivity function can give information about visual function not obtainable by conventional test procedures.

Adult↗
PubMed1993

Levodopa improves spatial contrast sensitivity in Parkinson's disease.

OBJECTIVE: To study the effect of levodopa on the visual contrast sensitivity of patients with Parkinson's disease. DESIGN: Contrast sensitivity of patients was measured before and after levodopa administration. Patient contrast sensitivity was compared with that of normal controls by repeated-measures analyses of variance. SETTING: Parkinson's disease research center associated with private neurology practice. PATIENTS: Fifteen patients with idiopathic Parkinson's disease (eight men, seven women; mean age, 71.8 years) and 22 normal controls (10 men, 12 women; mean age, 68.0 years) volunteered for the study. INTERVENTION: Levodopa/carbidopa (Sinemet). MAIN OUTCOME MEASURE: Change in contrast sensitivity of parkinsonian patients. RESULTS: Following levodopa treatment, the contrast sensitivity of parkinsonian patients improved significantly at the three lowest spatial frequencies tested (0.4, 1, and 2 cycles per degree). CONCLUSIONS: Levodopa improves low-frequency contrast sensitivity in parkinsonian patients. Initially deficient contrast sensitivity in such patients may be restored to near normal levels by levodopa therapy.

Aged↗
PubMed1981

Contrast sensitivity function in evaluation of visual impairment due to retinitis pigmentosa.

Spatial contrast sensitivity functions of 11 retinitis pigmentosa patients were studied. The patients represented 3 different stages of the disease: 1: in the very severely impaired patients the contrast sensitivity and grating resolution had decreased to a fraction of normal. 2: in severely impaired patients, who had lost peripheral field but had subjectively satisfactory vision in the central field, contrast sensitivity differed considerably from one patient to another, 3: some of the moderately impaired patients, who still had useful peripheral vision, had nearly normal contrast sensitivity in the central vision while they already had large ring scotomas. The severity of reduction in contrast sensitivity was poorly correlated with visual acuity, the size of the visual field and the age of the patient. Because contrast sensitivity function cannot be predicted by means of other clinical measurements, it should be included in evaluation of visual impairment due to retinitis pigmentosa. We also measured contrast sensitivity at low luminance levels: this procedure provided useful information for evaluation of vision in retinitis pigmentosa. The contrast sensitivity function of each patient agreed with the subjective view of the patient about his visual impairment and it also corresponded with the examiners' evaluation of the patient's performance in different visual and visuomotor tasks.

Adolescent↗
PubMed1999

Contrast sensitivity in patients recovered from central serous chorioretinopathy.

OBJECTIVE: To study contrast sensitivity in patients who have recovered from central serous chorioretinopathy (CSC). PATIENTS AND METHODS: Thirty-one patients who had recovered from CSC were examined with the Vistech and Pelli-Robson contrast sensitivity charts. The time from the onset of the active disease varied from 10 to 166 months (mean 60.4 +/- 42.0, SD). The visual acuity was 1.0 (logMar 0) or better. RESULTS: Contrast sensitivity of the affected eyes was significantly worse in the intermediate spatial frequencies of 3 and 6 cycles per degree (cpd) in the Vistech test compared to the fellow eyes (p = 0.032, 0.013, respectively). Contrast sensitivity of the affected eyes was significantly worse in all 5 spatial frequencies of the Vistech test and in the Pelli-Robson test compared to age-matched normal eyes (p = 0.006, 0.000, 0.000, 0.018, 0.000, 0.000, respectively). Contrast sensitivity of the fellow eyes was significantly worse in the spatial frequencies of 3 and 18 cpd in the Vistech test and in the Pelli-Robson test compared to age-matched normal eyes (p = 0.020, 0.019, 0.000, respectively). CONCLUSIONS: Contrast sensitivity does not seem to recover in all eyes after CSC even if the visual acuity has returned to normal. Therefore, contrast sensitivity testing is recommended for the patients complaining of visual impairment in spite of good visual acuity.

Adult↗
PubMed1983

Visual fields described by contrast sensitivity, by acuity, and by relative sensitivity to different orientations.

Sinewave grating contrast sensitivity was measured as a function of eccentricity and azimuthal angle for four orientations of gratings whose spatial frequencies ranged from 2 to 20 c/deg. Visual fields for cutoff spatial frequency were also mapped. Log contrast sensitivity fell off approximately linearly with eccentricity for all azimuths. Orientational differences in contrast sensitivity varied irregularly over the visual field and, though small for central vision, could reach as high as 25 dB in localized patches at eccentricities greater than about 12 degrees.

Adult↗
PubMed2006

Contrast sensitivity function and ocular higher-order wavefront aberrations in normal human eyes.

PURPOSE: To investigate the relation between contrast sensitivity function and ocular higher-order wavefront aberrations in normal human eyes. STUDY DESIGN: Prospective observational case series. PARTICIPANTS: Three hundred seven eyes of 161 normal subjects, ranging in age from 15 to 60 years (30.9+/-8.0 [mean +/- standard deviation]). METHODS: Ocular higher-order aberrations were measured for a 4-mm pupil using the Hartmann-Shack wavefront analyzer. The root-mean-square of the third- and fourth-order Zernike coefficients was used to represent comalike and spherical-like aberrations, respectively. We measured contrast sensitivity, low-contrast visual acuity (VA), and letter contrast sensitivity. From the contrast sensitivity data, the area under the log contrast sensitivity function (AULCSF) was calculated. Pupil diameter in a photopic condition was recorded using a digital camera. RESULTS: Multiple linear regression analysis revealed that comalike aberration (P = 0.002) was significantly associated with AULCSF, but spherical-like aberration (P = 0.200), age (P = 0.185), and photopic pupil diameter (P=0.252) were not. Comalike aberration showed a significant correlation with low-contrast VA (P<0.001), but spherical-like aberration (P = 0.293), age (P = 0.266), and pupil diameter (P = 0.756) did not. Comalike aberration was found to be significantly associated with letter contrast sensitivity (P<0.001), but spherical-like aberration (P=0.082), age (P = 0.370), and pupil diameter (P = 0.160) were not. CONCLUSIONS: In normal human eyes, comalike aberration of the eye significantly influences contrast sensitivity function.

Accommodation, Ocular↗