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Results for “Contrast Sensitivity”

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At least 667 records · Page 37Linked to original sources

PubMed1989

Letter contrast sensitivity in retinitis pigmentosa patients assessed by Regan charts.

Regan Contrast Sensitivity Letter Charts were used to assess the effects of reduced contrast and luminance on visual acuity in retinitis pigmentosa (RP) patients. Letter acuity was measured monocularly in 17 RP patients and in 14 age-similar normals using charts of three different contrast levels presented at each of four levels of illumination. Despite visual acuities of 20/40 or better under standard clinical test conditions, an appreciable number of RP patients were unable to identify any letters on the intermediate- and/or low-contrast Regan charts. For example, even at the recommended test luminance, 5 patients could not read any letters on the intermediate (11%) contrast chart, and 9 could not be scored on the low (4%) contrast chart. Consequently, the Regan charts were found to have limited usefulness in quantifying the exact extent of visual impairment in this group of RP patients. Nevertheless, our results document the degree of visual acuity loss that can be experienced by RP patients under conditions of low contrast and luminance.

Adolescent↗

PubMed2005

Smooth-pursuit eye movement and directional motion-contrast sensitivity in schizophrenia.

Although the occurrence of visual processing and eye-movement disorders in schizophrenia have been widely recognized, their relationship with the symptoms of schizophrenia is less well understood. In two experiments the relationship between directional-motion processing and smooth-pursuit eye movement was investigated in normal observers and in groups with positive and negative symptoms in schizophrenia. The first experiment measured linear smooth-pursuit eye movement at six target velocities from 5.0 to 30.0 degrees s(-1) and the second experiment measured directional motion-contrast sensitivity at three spatial (1.0, 4.0 and 8.0 c/deg) and five temporal (0.75, 3.0, 6.0, 12.0 and 18.0 Hz) frequencies in the same groups of observers. No significant differences were found between the control and positive-symptom group in directional motion-contrast sensitivity and smooth-pursuit eye movements. In comparison, a relationship was found between a significant reduction in directional motion-contrast sensitivity and significantly reduced smooth-pursuit eye movement in the negative-symptom group and serves to further cleave the distinction between positive and negative symptoms in schizophrenia. The relationship between visual motion processing and pursuit eye movement in the negative-symptom group was explained by a disorder in directional motion processing that fails to fully engage the pursuit eye movement system and reduces smooth pursuit eye-velocity gain.

Adult↗

PubMed2000

[Retreatment after PRK for low and medium myopia. Results and study of contrast sensitivity].

PURPOSE: To examine the results of retreatment with eximer laser photorefractive keratectomy (PRK) on refraction, visual acuity, haze, and contrast sensitivity. PATIENTS AND METHODS: Excimer laser photorefractive keratectomy was performed in 18 patients, once for one eye and twice for the other eye due to undercorrection or regression. Outcome was compared between the two eyes. RESULTS: Uncorrected visual acuity was above 20/40 in 94.4% of the retreated eyes. There was no statistical difference between the two eyes for haze and contrast sensitivity. CONCLUSION: Retreatment with laser photorefractive keratectomy is a safe procedure and should be performed when regression or undercorrection occurs after the first laser excimer treatment.

Adult↗

PubMed1986

A new photographic-based system for the measurement of contrast sensitivity.

A new photographic-based system has been developed for the measurement of contrast sensitivity in human vision. The system has several advantages over other photographic methods and is relatively easy and inexpensive to produce. This paper describes the design of the new system and the methods used in the production of the photographic prints. Preliminary tests show that full contrast sensitivity curves can be obtained with a small number of photographic prints and that these curves are very similar to those obtained using a carefully calibrated electronic pattern generator.

Form Perception↗

PubMed1995

Deriving channel gains from large-area sine-wave contrast sensitivity data.

A wealth of detection data can be accounted for by a spatial-vision model including a finite number of space-variant, spatial-frequency and orientation-selective channels of varying gains coupled with a detection rule involving probability summation over space and among channels. This paper shows that the detection of large-area, foveally fixated sine-wave gratings can be understood as if it occurred merely as a result of the activity of the subset of channels whose orientation matches that of the gratings, and operating under a peak-detection rule. This simplification makes it possible to show the theoretical relationship between the large-area sine-wave contrast sensitivity function, the channel gain function, and the channel modulation-transfer functions. It is also shown that the human visual system must have many more channels than are normally assumed in spatial-vision models, for otherwise the contrast sensitivity function would show significant bumps. An unlimited-channel model with a given mathematical form for the channels' modulation transfer functions is used to derive a mathematical expression for the (foveal) channel gain function from the large-area psychophysical sine-wave contrast sensitivity function.

Contrast Sensitivity↗

PubMed1994

Contrast sensitivity of the visual system in speckle imagery.

The contrast sensitivity function (CSF) of the whole visual system is determined with the use of coherent diffuse illumination. This function provides supplementary data about the effect of speckle on the ability of the visual system to perceive the spatial information contained in an image. The results show that speckle not only prevents perception of the finest details (highest frequencies) but also reduces the visibility of lower frequencies (especially where contrast is low). The difference between the CSF's determined with and without speckle is quantitatively very important. And the ratio between the two CSF's is a measure of the retinal ability to perceive contrast in the presence of speckle noise. The influence of the pupil size and luminance level on the CSF with speckle is studied and compared with the influence of the same parameters on the classical CSF.

Contrast Sensitivity↗

PubMed1993

GABA-ergic control of visual perception in healthy volunteers: effects of midazolam, a benzodiazepine, on spatio-temporal contrast sensitivity.

1. We studied the effects of midazolam (MDZ), a benzodiazepine, on spatio-temporal contrast sensitivity, choice reaction time, and mood visual analogue scales in healthy volunteers. 2. Eight extensively trained, healthy volunteers were included in a placebo-controlled cross-over double-blind trial of MDZ (0.15 mg kg-1). Treatments were injected intramuscularly and evaluations were performed before and 0.5, 1, 2, 3 and 4 h after drug administration. Spatio-temporal contrast sensitivity was measured using a micro-computer with appropriate software. Stimuli were vertical gratings with adjustable contrast, with spatial frequencies of 0.25, 1 and 4 cpd. Four conditions of temporal modulation were used: the grating was either static or drifting laterally with temporal frequencies of 1, 3 and 9 Hz. 3. An analysis of variance was performed on the data. As compared with placebo, MDZ induced an increase in choice reaction time and sedation (as assessed on visual analogue scales). From 0.5-4 h after the injection, MDZ produced an overall decrease in visual sensitivity, as compared with placebo. More specifically, MDZ preferentially affected medium to high spatial frequencies and low temporal frequencies. Several non-exclusive hypotheses may account for the results: 1) an increase in the size of the receptive fields, 2) a preferential effect on the visual parvocellular pathways which mediate the sensitivity to high spatial and low temporal frequencies.

Adult↗

PubMedDate not supplied

[Changes in contrast sensitivity in children with optic neuritis].

Changes of spatial contrast sensitivity (SCS) were studied in children with optic neuritis in the acute, convalescent, and remote periods of disease. A selective reduction of SCS of involved and intact eyes in the high frequency band was revealed, indicating the predominant involvement of the parvocellular subsystem of vision in optic neuritis. A correlation of SCS disorders with abnormalities of visual evoked potentials was revealed. The detected regularities indicate shifts on the part of the retrochiasmal structures in patients with optic neuritis, this being confirmed by studies making use of computer-aided tomography and magnetic imaging.

Adolescent↗

PubMed2005

Colour contrast sensitivity with different intraocular lens materials in the right and left eyes in same day surgery.

PURPOSE: To study possible differences in colour contrast sensitivity between different intraocular lens (IOL) materials with consecutive same day cataract surgery performed in the right and left eyes. METHODS: Central colour contrast sensitivity was measured with a computer graphics system along the protan, deutan and tritan axes. Thirty-four patients with cataract were studied. The patients were randomized to one of three groups: group 1 received a Clariflex (silicone) lens in one eye and an Akreos Fit (hydrophilic acrylic) lens in the other; group 2 received an Akreos lens in one eye and a Sensar AR40e (hydrophobic acrylic) lens in the other, and group 3 received a Clariflex lens in one eye and an AR40e lens in the other. Surgery was performed in both eyes on the same day. A postoperative questionnaire was distributed, asking the patients to describe any differences experienced between their two eyes. RESULTS: There were no significant differences between the three different IOLs in any colour axis. There were no complications of importance during surgery. Thirty-two of the 34 patients answered the questionnaire. Twenty-one patients experienced some difference between their two eyes in distance vision and 23 noticed differences in near vision. For distance vision, nine reported better vision in the eye with the Akreos IOL, eight in the eye with the Clariflex IOL lens and four in the eye with the AR40e IOL. For near vision, 12 preferred the Akreos lens, eight the Clariflex lens and three the AR40e lens. CONCLUSION: There were no significant differences between the three different IOLs in any colour axis.

Acrylic Resins↗

PubMed1993

Loss of contrast sensitivity in diabetic patients with LOCS II classified cataracts.

Contrast sensitivity function (CSF) was assessed in a population of diabetics with moderate cataracts to determine if CSF testing provides more information about visual dysfunction than Snellen or Lotmar interferometric visual acuity. With the Lens Opacities Classification Systems Version II (LOCS II) of cataract classification it was possible to grade accurately the type and severity of cataract and nuclear brunescence. The presence of statistically significant relationships between increasing LOCS II classification (worsening cataract) and diminished function, even when the regression model was controlled for Snellen visual acuity, supports the thesis that CSF measurements do provide more information about cataract related visual loss than Snellen acuity alone. Statistically significant (p < or = 0.05) relationships existed between different morphological types of cataract, nuclear colour, and CSF at specific frequencies. The frequencies affected differed with cataract type or nuclear colour, and with distance and near CSF.

Adult↗

PubMed2000

Assessing spatial vision - automated measurement of the contrast-sensitivity function in the hooded rat.

The contrast-sensitivity function (CSF) provides a concise and thorough description of an organism's spatial vision; it is widely used to describe vision in animals and humans, to track developmental changes in vision, and to compare vision among different species. Despite the predominance of rats in neuroscience research, their vision is not thoroughly studied due to the complexity of psychophysical measurement and a generally held notion that rat vision is poor. We therefore designed an economical and rapid method to assess the hooded rat's CSF, using a computer monitor to display stimuli and an infrared touch screen to record responses. A six-alternative forced-choice task presented trials in which a sine-wave grating (S+), varying in spatial frequency and contrast, was displayed at different locations along with five gray stimuli (S-). Nose pokes to the S+ but not the S- produced water reinforcers. Contrasts were tested at each spatial frequency with a simple adaptive procedure until stimulus detection fell below chance. Psychometric functions were obtained by maximum-likelihood fitting of a logistic function to the raw data, obtaining the threshold as the function's point of inflection. As in previous studies with rats, CSFs showed an inverse-U shape with peak sensitivity at 0.12 cyc/deg and acuity just under 1 cyc/deg. The results indicate the present computer-controlled behavioral testing device is a precise and efficient instrument to assess spatial visual function in rats.

Animals↗

PubMed1993

The effects of daily-wear contact lenses on contrast sensitivity in selected professional and collegiate female tennis players.

Contrast sensitivity (CS) has recently emerged as an important predictor of visual performance. Few studies, however, have been published involving CS and its role in vision for sport. The purpose of this investigation was to determine if significant differences occurred in CS between female professional and collegiate tennis players who wore daily-wear soft contact lenses (N = 10) and those players who wore no corrective lenses (N = 10) in competition as measured by the Stereo Optical Optec 2000 Vision Tester. Subjects were between the ages of 18 and 37 years. Mean ages were 21.76 (+/- 4.018) and 25.40 (+/- 5.379) years for those wearing lenses and those not, respectively. Each subject was preliminarily screened for SVA-distance, lateral/vertical phorias, stereopsis, and color perception. All subjects were within accepted limits. CS was assessed at 1.5, 3, 6, 12, and 18 cycles per degree (cpd). Each subject was assessed monocularly; eye initially assessed was determined randomly. A 2 x 2 factorial analysis of variance (alpha = .05) was used to analyze data. No significant differences were found between eyes. Significant differences were found at 3, 6, 12, and 18 cpd. It may be concluded that those female professional and collegiate tennis players wearing no corrective lenses were significantly higher in CS at intermittent and high spatial frequencies than those who wore daily-wear soft contact lenses in competition.

Adolescent↗

PubMed1985

Contrast sensitivity to drifting low spatial frequency gratings in central and peripheral retinal areas.

We measured contrast sensitivity to drifting sine wave gratings in central (20 degrees) and peripheral (from +/- 10 degrees to +/- 30 degrees) retinal areas. Low spatial frequencies were used (0.1-3 c/deg). The spatiotemporal sensitivity for spatial frequencies above 0.8 c/deg was found to be better in the central than in the peripheral retina. However, for spatial frequencies below 0.8 c/deg, the spatiotemporal contrast sensitivities of central and peripheral retinal areas were found to be the same. These results were obtained without scaling the peripheral gratings by the reciprocal of the cortical magnification factor.

Form Perception↗

PubMed1982

Arden contrast sensitivity testing in glaucoma.

Two hundred sixteen eyes (164 patients) were studied with the Arden printed contrast gratings to test Arden's hypothesis that an abnormal score would distinguish between eyes with and without glaucoma. Ninety-five eyes were normal and 75 eyes were glaucomatous; 46 eyes suspected of being glaucomatous were also studied to determine whether such eyes would score differently than eyes with normal intraocular pressures. No age-dependent trend in scoring was found in the different diagnostic categories, except with the age group younger than 40 years, which had consistently better contrast sensitivity. The tests were demonstrated to be reproducible over time and showed little or no intertester variability. Decreased contrast sensitivity was found in the glaucomatous eyes compared with normal eyes. The scores of the eyes suspected of being glaucomatous fell between the scores of the glaucomatous and normal eyes. Overlapping distributions among the three groups, however, limit the diagnostic value of the test.

Adult↗

PubMed1984

The effect of penetrating keratoplasty on contrast sensitivity in keratoconus.

Complaints of visual distortion often precede a decrement in visual acuity in keratoconus. We studied seven patients with keratoconus who had undergone keratoplasty in one eye and whose Snellen visual acuity measurements were equal in the grafted and nongrafted eyes. Subjects were examined clinically; we then measured contrast thresholds for seven spatial frequencies of computer-generated sinusoidal gratings after optimal contact lens correction. Results indicate that nongrafted keratoconic eyes demonstrate abnormal contrast sensitivity, even with good visual acuity measurements. Eyes with clear corneal grafts and with visual acuities comparable to nongrafted eyes fell within the 95% confidence limits of the normal contrast sensitivity curve. The findings confirm that corneal distortion or opacity in the optimally corrected keratoconic eye may account for notable visual dysfunction and that keratoplasty improves not only Snellen visual acuity but contrast sensitivity as well.

Adult↗

PubMed1999

Long-term changes in retinal contrast sensitivity in chicks from frosted occluders and drugs: relations to myopia?

Experiments in animal models have shown that the retinal analyzes the image to identify the position of the plane of focus and fine-tunes the growth of the underlying sclera. It is fundamental to the understanding of the development of refractive errors to know which image features are processed. Since the position of the image plane fluctuates continuously with accommodative status and viewing distance, a meaningful control of refractive development can only occur by an averaging procedure with a long time constant. As a candidate for a retinal signal for enhanced eye growth and myopia we propose the level of contrast adaptation which varies with the average amount of defocus. Using a behavioural paradigm, we have found in chickens (1) that contrast adaptation (CA, here referred to as an increase in contrast sensitivity) occurs at low spatial frequencies (0.2 cyc/deg) already after 1.5 h of wearing frosted goggles which cause deprivation myopia, (2) that CA also occurs with negative lenses (-7.4D) and positive lenses (+6.9D) after 1.5 h, at least if accommodation is paralyzed and, (3) that CA occurs at a retinal level or has, at least, a retinal component. Furthermore, we have studied the effects of atropine and reserpine, which both suppress myopia development, on CA. Quisqualate, which causes retinal degeneration but leaves emmetropization functional, was also tested. We found that both atropine and reserpine increase contrast sensitivity to a level where no further CA could be induced by frosted goggles. Quisqualate increased only the variability of refractive development and of contrast sensitivity. Taken together, CA occurring during extended periods of defocus is a possible candidate for a retinal error signal for myopia development. However, the situation is complicated by the fact that there must be a second image processing mode generating a powerful inhibitory growth signal if the image is in front of the retina, even with poor images (Diether, S., & Schaeffel, F. (1999).

Adaptation, Ocular↗

PubMed1992

Improvement of contrast sensitivity with yellow filter glasses.

Yellow filter glasses, often sold as "antifog" or "safety" glasses at department stores and other retail outlets, are claimed to improve contrast sensitivity and the yield of visually perceived objects, particularly under poor conditions (e.g., fog, rain and twilight), by enhancing contrast. These claims were tested in 15 healthy subjects (30 eyes) aged 26 to 58 (mean 42.5) years with the Vision Contrast Test System (VCTS 6500), first with and then without yellow filter glasses. Testing was done with commercial antifog glasses and frame-mounted, hand-held filter glasses of CR (Columbia resin) 39 quality with a yellow tint made by an optician. Contrast sensitivity was found to be significantly improved with yellow filter glasses (p less than 0.0001). The use of yellow filter glasses may safely be recommended to patients who report subjective improvement in contrast vision with such glasses.

Adult↗

PubMedDate not supplied

Pharmacological separation of mechanisms contributing to human contrast sensitivity.

Two basic types of cholinergic receptor have been identified in nervous systems: nicotinic and muscarinic. In the mammalian visual system, the balance of evidence suggests that nicotinic activity is associated primarily with transmission and processing of information while muscarinic activity reflects modulatory influences arising in the brainstem and basal forebrain. We have measured contrast sensitivity functions using a two-alternative forced-choice procedure in young human volunteers with and without administration of nicotine (1.5 mg by buccal absorption) or the muscarinic antagonist scopolamine (1.2 mg orally). Scopolamine elevates contrast-detection thresholds uniformly at all spatial frequencies, consistent with blocking of a nonspecific arousal system. Nicotine, in contrast, improves sensitivity at low spatial frequencies (below about 4 cycle/deg); at higher spatial frequencies sensitivity is, if anything, impaired. Using counterphase gratings, we find that scopolamine elevates thresholds uniformly at all temporal frequencies. Nicotine lowers thresholds at high but not low temporal frequencies. The results obtained with nicotine suggest that contrast sensitivity reflects the activity of two mechanisms, or sets of spatiotemporal filters, that are pharmacologically distinct, the contrast sensitivity function reflecting the envelope of their sensitivities.

Administration, Oral↗