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PubMedDate not supplied

From retina to response: contrast sensitivity and memory retrieval during visual word recognition.

Twenty-four young adults (M = 19.5 years) and 24 older adults (M = 68.4 years) performed a word/nonword classification task (i.e., lexical decision) in which a single letter-string was presented on each trial. Estimates were obtained of the time required to retrieve information regarding the orthography (pronounceability) and meaning of the letter-string. A measure of subjects' spatial resolution ability (contrast sensitivity) was also obtained. In the lexical decision task, the older adults' word recognition speed was slower than that of the young adults overall, but there was no age-related slowing associated specifically with the retrieval of either orthographic or semantic information. The similarity of the two age groups' retrieval estimates was independent of whether a manual or vocal response was required. An age-related change in the shape of the contrast sensitivity function was present. The age differences in the speed of word recognition, however, were not attributable to contrast sensitivity.

Adolescent↗

PubMed2004

[Changes in contrast sensitivity in glaucoma patients].

OBJECTIVE: To evaluate changes of temporal contrast sensitivity (TCS) in patients with glaucoma. MATERIAL AND METHOD: We measured TCS (for 10, 20 and 30 Hz frequencies) in 57 eyes with glaucoma using a prototype that produces a red colour flicker stimulus (lambda = 626 nm) projected in the central 320 of the visual field. In all patients measurements were undertaken for the visual acuity and intraocular pressure. Also the optic disc was evaluated (including C/D ratio), as well as the visual field using the 24/2 program of the Humphrey automated perimeter. RESULTS: For all tested frequencies we computed sensitivity and specificity of the test S < 0 as diagnostic tool for glaucoma. The sets of determination with 30 Hz flicker stimulus have a validity score of 83.8%. We also evaluated the correlation curves between the S score, C/D ratio and mean deviation from automated perimetry. CONCLUSIONS: Patients with glaucoma present a significant drop of the S score for all three tested frequencies. The S score positively correlates with mean deviation (MD) and negatively with C/D ratio reflecting thus diffuse alterations of the magnocellular system. The decrease of the S score in the 30 Hz set of data is major and S < 0 as a diagnostic test has very good sensitivity and specificity. S score might be used in screening for glaucoma as well as monitoring progression of the disease (rapid test, low cost, good validity).

Analysis of Variance↗

PubMed1986

Radial keratotomy and glare effects on contrast sensitivity.

After radial keratotomy (RK) to correct myopia, some patients complain of 'glare'. Effects of a glare source on contrast sensitivity were measured in fifteen patients after unilateral RK. With each eye, determinations were made of the contrast required for detection of steady gratings (spatial frequencies of 0.7 and 2.9 cycles/deg), and for detection of flicker (unpatterned field flickering at rates of 8, 16, and 32 Hz). Grating or flicker was presented on a centrally fixated 4 deg test target (34 cd/m2 mean luminance), surrounded by a diffuse glare source (1700 cd/m2 mean luminance). For each stimulus, contrast thresholds were determined with glare-source off and with glare-source on. 'Glare loss' was defined as the decrement in contrast sensitivity measured with the glare source on. Significant findings were: (1) Both eyes showed glare losses for detection of gratings and for detection of flicker; (2) Spectacle lenses increased glare losses both for gratings and for flicker; (3) The RK eye showed a larger glare loss for flicker than the unoperated eye, but a smaller glare-loss for gratings; (4) For both flicker and gratings, glare loss tended to be greater in the RK eye, compared to the unoperated eye, in subjects who had larger pupil diameters in the testing situation; (5) The psychophysical measurements obtained in this study were not significantly correlated either with a questionnaire index of glare complaints or with the score obtained with the Miller-Nadler GlareTester.

Adult↗

PubMed1997

Decreased contrast sensitivity in normal tension glaucoma determined by pattern visually evoked cortical potentials.

Little is known about the central visual function of patients with normal tension glaucoma (NTG). We estimated the contrast sensitivity of patients with NTG and normal subjects with the use of pattern visually evoked cortical potentials (PVECPs). PVECPs were recorded using checkerboard pattern reversal system display on television monitor of check size 15', 60' and frequency 3 reversals per second and contrast varied in 7 steps. Our results show that a significant delay of the P100 component for 60' check size in the NTG group was found at every contrast level (P < 0.05). Contrast threshold was determined as the value to obtain a criterion peak latency from a regression line calculated within a contrast range from 10% to 56%. The contrast threshold for both check sizes of the NTG group showed an increased threshold (P < 0.05). We conclude that contrast sensitivity decreased in NTG as determined by PVECP. The PVECP was a sensitive test for detecting the functional abnormalities of NTG.

Contrast Sensitivity↗

PubMed1987

Contrast sensitivity, acuity, and the perception of 'real-world' targets.

A major assumption underlying the use of contrast sensitivity testing is that it predicts whether a patient has difficulty seeing objects encountered in everyday life. However, there has been no large-scale attempt to examine whether this putative relationship actually exists. We have examined this assumption using a clinic based sample of adults aged 20-77 years. Contrast thresholds were measured for both: (1) gratings of 0.5-22.8 cycles/degree; and (2) real-world targets (faces, road signs, objects). Multiple regression techniques indicated that the best predictors of thresholds for real-world targets were age and middle to low spatial frequencies. Models incorporating these variables accounted for 25-40% of the variance. Although acuity significantly correlated with thresholds for real-world targets, the inclusion of acuity as a predictor variable did not improve the model. These data provide direct evidence that spatial contrast sensitivity can effectively predict how well patients see targets typical of everyday life.

Adult↗

PubMedDate not supplied

[A new method of assessing contrast sensitivity in patients with eye diseases].

A new method for examining spatial contrast sensitivity (SCS) is described, making use of the display of an IBM-compatible computer, on which sinusoidal patterns are presented: achromatic and chromatic red, green, blue against the black background at a frequency of 0.5 to 22 cycles/degree. In health similarity of curves to the achromatic and chromatic patterns was observed, with the maximal sensitivity at spatial frequencies from 2 to 8 cycles/degree and a reduction at low and high spatial frequencies. In patients with the initial open-angle glaucoma the SCS at the high spatial frequencies was reduced for all colors with "dips" at the medium spatial frequencies in response to the blue pattern. In patients with albinism the SCS to achromatic and chromatic patterns were appreciably decreased in the entire range of spatial frequencies and absent at all in the range of high spatial frequencies. The method is recommended for investigating the channels of achromatic and chromatic spatial sensitivity, detecting the contribution of color receptors to the color contrast, and for the initial diagnosis of diseases of the retina and optic nerve.

Albinism↗

PubMed1988

Effect of radial keratotomy on the contrast sensitivity function.

A group of six patients had the radial keratotomy (RK) procedure carried out on one eye only as part of the Prospective Evaluation of Radial Keratotomy (PERK) study. Contrast sensitivity was measured in the operated and unoperated eyes of these patients under conditions of maximum correction and no over-correction. Analysis of variance indicated a significant reduction in the contrast sensitivity function (CSF) of the operated eye postsurgically when compared to the operated eye for all patients. Analysis of results for individual patients indicated that three of the six patients showed significant reductions in CSF between the two eyes. Reasons for these changes are offered in terms of the change in glare produced by the surgical procedure and the difference in spherical aberration of the eye.

Adult↗

PubMed1984

The effect of a yellow filter on contrast sensitivity.

Most previous studies have found no visual advantage for the use of yellow filters. This study reports the effect of wearing a long-pass yellow filter on monocular spatial contrast sensitivity under photopic and mesopic conditions. Contrast sensitivity was improved with the yellow filter under photopic conditions but not significantly at most spatial frequencies under mesopic conditions.

Adult↗

PubMed1988

Contrast sensitivity after epikeratophakia.

Epikeratophakia is a rapidly evolving surgical procedure for the refractive correction of aphakia. Even when Snellen acuity after epikeratophakia is normal, patients often report a subjective degradation of the visual image through the surgically corrected eye. To further define visual performance in the patient with optically successful epikeratophakia, we examined contrast sensitivity in two patients surgically corrected for monocular aphakia. Contrast thresholds were measured over a range of spatial frequencies using both computer-generated sinusoidal gratings and a commercially available wall chart system. The eye with epikeratophakia in each case was compared with the opposite normal eye with comparable acuity. One patient was also tested prospectively in the same eye both before and after surgery. Data demonstrate a depression of the contrast sensitivity function in the middle and high spatial frequencies induced by the placement of an epikeratophakia lenticule when compared with the normal eye or contact lens-corrected, preoperative aphakic eye with comparable good acuity. These findings may explain the subjective experience of epikeratophakia patients.

Adult↗

PubMed1999

Functional complaints, visual acuity, spatial contrast sensitivity, and glare disability in preoperative and postoperative cataract patients.

PURPOSE: To quantify cataract patients' functional visual complaints and correlate them with their objective glare disability and spatial contrast sensitivity (SCS) scores. SETTING: Sir Mortimer B. Davis Jewish General Hospital. Montreal, Quebec, Canada. METHODS: Thirty patients scheduled for cataract surgery with a visual acuity of 20/70 or better at the time of patient selection and no other ocular pathology were evaluated objectively and subjectively for visual function preoperatively and within 3 months postoperatively. Objective measures of SCS and visual acuity in the presence and absence of glare were obtained with the Optec 3000 vision tester. Subjective visual function was evaluated with the Activities of Daily Vision Scale (ADVS), a questionnaire that evaluates patients' visual function by assessing the degree of difficulty they experience in performing tasks involving distance vision, near vision, and glare conditions. RESULTS: Preoperatively, patients had decreased visual acuity and SCS in the presence of glare. The ADVS scores were correlated with visual performance. Postoperatively, there was a statistically significant improvement in all dependent measures (i.e., visual acuity and SCS in the presence of glare) as well as in the subjective report of visual performance assessed by the ADVS. CONCLUSION: Spatial contrast sensitivity, glare disability, and the ADVS questionnaire should be considered as adjuncts to visual acuity testing in evaluating certain cataract patients.

Adult↗

PubMed1989

Comparison of contrast sensitivity between posterior chamber lenses of silicone and PMMA material.

Seventeen patients received a posterior chamber lens of PMMA in one eye and a silicone lens (Staar Surgical Co.) in the other. Contrast sensitivity was examined in both eyes in order to detect differences with respect to the material used for lens implantation. An attempt was made to exclude any changes in the eyes that were not due to lens implantation and that might possibly have an influence on the result. A paired T-test was performed for each spatial frequency. No statistically significant difference was found between the two materials with regard to contrast sensitivity.

Aged↗

PubMed1981

Contrast sensitivity function of preschool children.

A procedure specifically adapted for children of preschool age has been used to measure contrast sensitivity in emmetropic children aged 3 to 5 years. Mothers of the children acted as adult observers using the same procedure. The results show that the contrast sensitivity function of adults and children is very similar, sensitivity for the children being slightly lower than that for adults at all spatial frequencies. The sensory and cognitive factors involved in these differences are discussed.

Adult↗

PubMed1983

Contrast sensitivity in monocular glaucoma.

The results of this selected group of glaucoma patients demonstrate that the effect of glaucoma on the contrast sensitivity can be assessed only after careful exclusion of all other causes for decrease in contrast sensitivity. Further development of methods is necessary.

Aged↗

PubMed2006

Wavefront analysis and contrast sensitivity of aspheric and spherical intraocular lenses: a randomized prospective study.

PURPOSE: To compare visual performance, total and high order wavefront aberrations (coma, spherical aberration, and other terms), and contrast sensitivity in 120 eyes implanted with one monofocal aspheric intraocular lens (IOL) and two spherical IOLs. DESIGN: Randomized prospective study. METHODS: Sixty patients were randomized to receive three IOL types: Alcon AcrySofIQ (40 eyes), AcrySofNatural (40 eyes), and advanced medical optic (AMO)Sensar (40 eyes). Complete ophthalmologic examination including uncorrected visual acuity (UCVA), best-spectacle corrected visual acuity (BSCVA), corneal topography, and wavefront analysis were performed preoperatively, 30 days, and 90 days postoperatively. Pelli-Robson chart test and functional acuity contrast testing (FACT-Optec6500) were performed approximately 50 days after surgery. Statistical analyses were performed using analysis chi(2), analysis of variance (ANOVA), and multiple comparisons Tukey test. RESULTS: After 90 days, all eyes had postoperative BSCVA > or =20/32. The AcrySofIQ IOL showed statistically significant less induction of spherical aberration (P < .001) when compared with the AMOSensar and the AcrySofNatural IOLs. The AMOSensar presented significantly less spherical aberration then the AcrySofNatural (P < .05). The AcrySofIQ also had lower values of total and high-order aberration (HOA) (P < .05) when compared with the AMOSensar and the AcrySofNatural. The mean values of trefoil 9, coma, and HOA root mean square (RMS) decreased between one and three months (P < .001, P < .001, P = .023, P < .001, respectively) in all groups. Mean Pelli-Robson contrast sensitivity values in photopic condition were similar between the groups. The AcrySofIQ showed better results in 3cpd spatial frequency in mesopic condition using FACT-Optec 6500 (P = .008), although there were no statistical differences in photopic and mesopic with glare conditions.

Aged↗

PubMed1988

The effect of radial keratotomy on contrast sensitivity.

In the period after surgical correction of myopia and astigmatism in 30 patients (44 eyes) by radial keratotomy, contrast sensitivity deteriorated slightly. The disturbances, however, were transitory, and the general trend was toward restoration of function. Strict adherence to an adequate operative technique prevented a marked decline in contrast sensitivity. The decrease must be considered before surgery, particularly in patients who need a high degree of fine motor control.

Adult↗

PubMed1997

Development of spatial frequency tuned "covariance" channels: individual differences in the electrophysiological (VEP) contrast sensitivity function.

We investigated the spatial frequency tuned channels underlying the contrast sensitivity functions (CSFs) of adults and infants. CSFs were measured in adults and in 8-, 14-, 20-, and 32-week-old infants, using the swept-contrast visual evoked potential (sweep-VEP). At each age, 8 to 21 subjects provided complete data. Subjects viewed achromatic sine wave gratings (0.3 to 8 c/deg) on a 20 degrees field presented on a CRT. Gratings were counterphased at 12 reversals/s (6 Hz). The second harmonic response was used to interpolate thresholds. We computed statistical "sources" of individual variability (or factors) underlying CSFs, then calculated the number, nature (discrete vs. continuous) and frequency tuning of "covariance" channels. CSFs from adults each contained three spatial frequency tuned covariance channels, consistent with psychophysical results spanning a similar spatial frequency range. Covariance channels in infants shifted upward in spatial frequency with age, with rapid shifts occurring between 8 and 14 weeks. The change in scale coincided with, and was probably determined by, developmental cone migration into the fovea and growth in eye size.

Adult↗

PubMed1992

[Discrete media clouding and its effect of contrast transfer coefficients, the pattern ERG and contrast sensitivity].

As a model for our study we selected 11 pseudophacic patients with secondary cataracts who experienced good postoperative visual acuity after extracapsular cataract extraction. Besides best visual acuity and contrast sensitivity Pattern-ERG (PERG) and Contrast-Transfer-Ratio (CTR) were measured before and after YAG-Kapsulotomy was performed. Visual acuity and contrast sensitivity increased in all patients after treatment, whereas CTR increased in eight patients. PERG was measured in five patients, in two cases its amplitudes were higher, the other measurements revealed unchanged or lower amplitudes. Our model shows that in addition to the usual psychophysic tests, with CTR and PERG there are objective methods available to measure discrete opacities of the visual system.

Cataract↗

PubMed2001

Contrast sensitivity function and image discrimination.

A previous study tested the validity of simulations of the appearance of a natural image (from different observation distances) generated by using a visual model and contrast sensitivity functions of the individual observers [J. Opt. Soc. Am. A 13, 1131 (1996)]. Deleting image spatial-frequency components that should be undetectable made the simulations indistinguishable from the original images at distances larger than the simulated distance. The simulated observation distance accurately predicted the distance at which the simulated image could be discriminated from the original image. Owing to the 1/f characteristic of natural images' spatial spectra, the individual contrast sensitivity functions (CSF's) used in the simulations of the previous study were actually tested only over a narrow range of retinal spatial frequencies. To test the CSF's over a wide range of frequencies, the same simulations and testing procedure were applied to five contrast versions of the images (10-300%). This provides a stronger test of the model, of the simulations, and specifically of the CSF's used. The relevant CSF for a discrimination task was found to be obtained by using 1-octave Gabor stimuli measured in a contrast detection task. The relevant CSF data had to be measured over a range of observation distances, owing to limitations of the displays.

Adult↗