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Results for “Contrast Sensitivity”

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PubMed2001

Can contrast sensitivity functions in dyslexia be explained by inattention rather than a magnocellular deficit?

We examined whether data demonstrating contrast sensitivity losses in dyslexia that have been interpreted as evidence for loss of magnocellular visual function could be explained by inattention. Computer simulations of observers with poor concentration yielded inflated estimates of threshold that were a constant proportion of the true threshold across spatial frequencies. Data from many, but not all, studies supporting the magnocellular deficit theory are well described by these simulations, which predicted no interaction between observer group and spatial frequency. Some studies have reported significant interactions, but suffer from statistical deficiencies. This compromises some of the evidence for a magnocellular deficit in dyslexia derived from studies of threshold contrast sensitivity.

Analysis of Variance↗

PubMed1993

Contrast sensitivity in elderly subjects with a diagnosed ocular disease.

In a random sample of 3283 subjects, 1266 right eyes and 1334 left eyes were diagnosed as having one of the following: age-related macular degeneration (ARMD), cataract, or glaucoma. In this same sample 1369 right eyes and 1312 left eyes had no ocular disease. All eyes had their contrast sensitivity measured using the Arden-type gratings manufactured by The American Optical Corporation. This is a large sample survey and although prevalence rates for the diseases examined may be inferred, this must be carried out with caution. I found for those eyes where the disease interfered with the integrity of the retina (ARMD, glaucoma) the mean contrast sensitivity scores were higher, in the middle and upper frequencies, than for those eyes with lens opacities. For frequencies above 0.4 cpd contrast sensitivities associated with diseased eyes were significantly (p < 0.001) reduced when compared to the same measures obtained on nondiseased eyes.

Aged↗

PubMed1976

The measurement of spatial contrast sensitivity in cases of blurred vision associated with cerebral lesions.

Thirty-five patients with known cerebral lesions complained of recently acquired blurred vision. None of them had evident oculomotor or pupillary abnormalities, and each had intact central fields and normal visual acuity by conventional standards. Examination of spatial contrast sensitivity was carried out with sinusoidal grating patterns, by determining the minimum contrast between alternate light and dark bars required to distinguish the pattern from a homogeneous field. This was done at each of several spatial frequencies which were established by varying the width of the bars and hence the coarseness of the pattern. The contrast sensitivities were plotted as "visuograms" which, by analogy to audiograms, record the sensitivities in comparison to normal standards. Of the 35 patients, most showed significant losses, amounting to greater than 50 per cent elevation of contrast thresholds. Eighteen showed high frequency losses; 11 had uniform reductions over the entire visible spatial frequency range and 6 had selective frequency losses in the intermediate frequency ranges. These defects in spatial contrast sensitivity, which were not predictable from standard acuity scores, indicate that the visual symptoms in our patients may have been caused by damage to frequency-selective neural elements in the central visual systems. The method may be used to advantage in clinical investigations as well as in physiological investigations of the functional pathways subserving central vision.

Adolescent↗

PubMed1984

Large-sample norms for contrast sensitivity.

A portable microprocessor-controlled instrument automatically measured the static and dynamic contrast sensitivity functions (CSF's) of 265 observers for a normal population at the Dayton Air Fair and Air Force Museum. Repeat measures for six observers taken 6 months later show small, nonsystematic differences from original measurements. Median values of contrast sensitivity as well as regions encompassing 75 of 90% of our sample are shown.

Adult↗

PubMed1987

Regional threshold contrast sensitivity within the central visual field in optic neuritis.

Contrast sensitivity was measured at nine locations within the central 10 degrees of the visual field in cases of recovered optic neuritis having varying degrees of residual deficit. A sample of 82 patches of visual field was obtained in 14 cases. Circular patches of vertically orientated sinusoidal gratings, 2.5 degrees in diameter, were used. The gratings were modulated in time at 8 Hz and the effect of spatial frequency on the threshold loss determined at each visual field location. As anticipated from what is known of visual field changes in the disorder there was considerable variation in the magnitude of the contrast threshold elevation at different locations in the visual field in any one case. The variability was more marked in cases with greater overall deficit. Three types of spatial loss were encountered. The most common was a loss which increased at higher spatial frequencies, found in 65 of the 82 patches of visual field examined. In 11 the loss was unaffected by spatial frequency and in the remaining 6 the loss was maximal at an intermediate spatial frequency. There was no instance of a loss maximal at low spatial frequencies. Overall the results indicate that sensitivity to higher spatial frequencies is more likely to be impaired following an attack of optic neuritis. In the combined results the effect of spatial frequency on the threshold elevation was statistically significant at all eccentricities (P less than 0.001). Analysis of the combined results revealed no difference in the mean contrast sensitivity loss at eccentricities of zero, 3.75 degrees or 7.5 degrees for intermediate and low spatial frequencies. There is no evidence from these results to suggest that the central foveal projection (papillomacular bundle) is more likely to be affected following an attack of optic neuritis than the projections of other eccentricities within the central 10 degrees as far as mechanisms subserving luminance vision are concerned at these spatial frequencies. Overall there was slightly greater reduction in acuity within the central 5 degrees than at 7.5 degrees eccentricity (P less than 0.05). This may be accounted for by the finding that higher spatial frequencies are more affected, rather than being related to eccentricity per se.

Demyelinating Diseases↗

PubMed1991

Spatial contrast sensitivity in Alzheimer's disease: a comparison of two methods.

The present study was designed to compare the contrast sensitivity functions (CSF) obtained with the Nicolet CS2000 and the Vistech VCTS6500 for a sample (N = 25) of patients diagnosed with probable Alzheimer's disease (AD) and a sample (N = 25) of healthy elderly adults. With the Nicolet, CSF were determined for gratings presented under static and rapidly counterphased (7.5 Hz) conditions. All research participants were able to complete the Vistech test. However, 13.7 and 7.4% of the original samples of Alzheimer patients and healthy adults, respectively, did not yield usable data. Both test instruments showed uniformly low contrast sensitivities for the AD group. The results support the proposition that AD involves a primary visual disturbance and suggest that the Vistech chart can be used with a broader range of patients for initial screening.

Aged↗

PubMed1983

Age, the eye, and the visual channels: contrast sensitivity and response speed.

Age differences in spatial vision were examined by establishing contrast sensitivity functions for young and old adults. In addition, differences in the speed of operation of the different visual channels and their contribution to age differences in reaction time were assessed in a comparison of response speed to sinusoidal gratings of varied spatial frequency. An age-related loss in contrast sensitivity was observed primarily for stimuli of intermediate and high spatial frequency, an effect apparently due mostly to age-related optical differences. Reaction time varied markedly as a function of spatial frequency for the older participants, an outcome only partly attributable to age differences in target visibility. These data indicate a slowing in the speed of operations of individual visual channels and/or a change in the relationship between visual channel classes. These findings also raise a question in regard to the meaning and comparability of any studies that have used measures of response latency to the figural aspects of stimuli.

Adolescent↗

PubMed1990

Visual acuity and contrast sensitivity of the S cone pathway: preliminary measures with letter charts.

Letter charts were used to measure visual acuity and peak contrast sensitivity of the short wavelength sensitive (S cone)-pathway. The accommodative response was monitored retinoscopically. The mean visual acuity (0.92 logMAR) and spatial contrast threshold (8.7%) were comparable to values reported elsewhere, and variability was relatively low. Both S-pathway acuity and contrast sensitivity were selectively reduced in one patient with central serous retinopathy and in another with retinitis pigmentosa. These simple spatial tests offer an additional index of S-pathway integrity which will be useful for detection and evaluation of ocular disease.

Accommodation, Ocular↗

PubMed1984

An anticipated threshold technique for measuring contrast sensitivity.

A new psychophysical procedure for assessing contrast sensitivity rapidly and reliably is reported. The technique consists of increasing the contrast of a conventional sine wave grating according to the parameters set in a computer implemented algorithm. During the first half of a trial, the contrast increases quickly to a point just below an expected threshold, and in the second stage the contrast increases slowly until a threshold is reached. Details and advantages of the algorithm are presented as well as a comparison of data generated by this and other techniques.

Computers↗

PubMed2005

Association between intensity of posterior capsule opacification and contrast sensitivity.

PURPOSE: To investigate the correlation between change in contrast sensitivity (CS) and difference in objective posterior capsule opacification (PCO) score before and after Nd:YAG laser capsulotomy. DESIGN: Prospective interventional case series. METHODS: CS (Functional Acuity Contrast Test, or FACT, chart), distance visual acuity (Early Treatment Diabetic Retinopathy Study [ETDRS] chart), and pupil size of 30 pseudophakic eyes with PCO of varying intensity were measured before and after capsulotomy. Digital retroillumination images were taken, and the area corresponding to the pupil size was evaluated with an automated PCO analysis program known as AQUA. RESULTS: The correlation between change in PCO score and change in CS was highest (r = 0.85) for row B on the FACT chart and lowest (r = 0.09) for row E. The correlation with change in ETDRS visual acuity was 0.57. CONCLUSIONS: Objective PCO assessment by an automated image analysis system correlates well with PCO-induced loss of CS and is therefore an appropriate method for clinical studies on the development and prevention of PCO.

Cataract↗

PubMed2005

Magnocellular channel subserves the human contrast-sensitivity function.

There is evidence that the human contrast-sensitivity function (CSF) is mediated by the spatiotemporal characteristics of magno and parvo neurons early in the visual pathway. In this study we use a measure of contrast gain derived from simple reaction times, to investigate the neural substrates of suprathreshold performance. The results reveal the activity of two mechanisms having distinctly different contrast-gain characteristics. Comparing these to neurophysiological data, we find that the magnocellular system dominates close-to-threshold detection and probably forms the basis of the achromatic CSF, whereas the parvocellular system dominates detection at higher contrasts, when the magnocellular system saturates.

Adult↗

PubMed1995

Peripheral contrast sensitivity for dynamic sinusoidal gratings in early glaucoma.

Automated contrast thresholds were established for dynamic, 2 reversals per sec phase-shifted, sinusoidal gratings in a 5 degrees circular test field centred 7.5 degrees from the fixation point in six positions in the visual field in 16 patients (age 56-76 years) with clinically established (optic disc or nerve fibre layer damage) early glaucoma, without visual field defects. For reference, contrast thresholds were also obtained in 16 sex-matched and age-matched controls. For all three spatial frequencies, thresholds were raised in the glaucoma group (0.5 c/deg: p = 0.0034-0.041, 2 positions n.s.; 1.0 c/deg: p = 0.0093-0.049, 1 position n.s.; 2.0 c/deg: p = 0.0011-0.041, 1 position n.s.). Deficiencies did not correlate to glaucoma type (simplex vs capsular), intraocular pressure level at examination, visual acuity, or local therapy (beta-blockers vs miotics). In the glaucoma group, there was a general loss of contrast sensitivity in all six positions tested in the visual field, reflected in roughly similar threshold elevations. Losses appeared slightly greater in the lower hemi-field. Definite contrast threshold elevations from the early glaucomatous process were established in this group of glaucoma patients without visual field defects. However, the method was considered to be of less value in glaucoma detection for individual subjects, due to the large overlap in threshold values between glaucoma patients and controls.

Aged↗

PubMed1989

The contrast sensitivity gradient across the human visual field: with emphasis on the low spatial frequency range.

The regional variation of contrast sensitivity along the greater extent of each of the four principal hemi-meridia of the normal human eye was determined under photopic conditions using horizontally-orientated sinusoidal grating stimuli. The stimuli were well localized in space and frequency, and special attention was paid to the low spatial frequency range. The results confirm that contrast sensitivity is maximal for central vision for all test spatial stimuli. Extra-foveal fall-off in sensitivity can be represented as a linear function of eccentricity if the latter is expressed in relative units (i.e. periods of the stimulus). The regional variation parameter depends upon whether the horizontal or vertical field is tested and upon the spatial frequency of stimulation. The visible spatial frequency range (0.05-24 c/deg) can be approximately described by just three different rules. The fact that more than one rule is found bears upon current models of the functional organization of the visual system.

Contrast Sensitivity↗

PubMed1995

Contrast sensitivity and spatial frequency response of primate cortical neurons in and around the cytochrome oxidase blobs.

The striate cortex of macaque monkeys contains an array of patches which stain heavily for the enzyme cytochrome oxidase (CO blobs). Cells inside and outside these blobs are often described as belonging to two distinct populations or streams. In order to better understand the function of the CO blobs, we measured the contrast sensitivity and spatial frequency response of single neurons in and around the CO blobs. Density profiles of each blob were assessed using a new quantitative method, and correlations of local CO density with the physiology were noted. We found that the CO density dropped off gradually with distance from blob centers: in a typical blob the CO density dropped from 75% to 25% over 100 microns. Recordings were confined to cortical layers 2/3. Most neurons in these layers have poor contrast sensitivity, similar to that of the parvocellular neurons in the lateral geniculate nucleus. However, in a small proportion of layers 2/3 neurons we found higher contrast sensitivity, similar to that of the magnocellular neurons. These neurons were found to cluster near blob centers. This finding is consistent with (indirect) parvocellular input spread uniformly throughout layers 2/3, and (indirect) magnocellular input focused on CO blobs. We also measured spatial tuning curves for both single units and multiple unit activity. In agreement with other workers we found that the optimal spatial frequencies of cells near blob centers were low (median 2.8 c/deg), while the optimal frequencies of cells in the interblob regions were spread over a wide range of spatial frequencies. The high cut-off spatial frequency of multi-unit activity increased with distance from blob centers. We found no correlation between spatial bandwidth and distance from blob centers. All measured physiological properties varied gradually with distance from CO blob centers. This suggests that the view of blob cells subserving visual functions which are entirely distinct from non-blob cells may have to be reevaluated.

Animals↗

PubMed1986

Changes in the contrast sensitivity of an amblyopic eye after losing the other normal eye.

A man aged 17 had an amblyopic left eye with central fixation and lost his normal right eye by an accident. After the accident, spontaneous improvement of the visual acuity of the amblyopic left eye was rapid. Just after the accident, overall contrast sensitivity of the left eye was considerably less than that of a normal adult. Improvement of the contrast sensitivity was recorded first at low spatial frequencies and then at high spatial frequencies. However, the contrast sensitivity at medium spatial frequencies remained less than that of a normal adult. These results suggest that lateral inhibitory processes may be relatively undeveloped or receptive fields do not develop to be as small as those of normal adults.

Adaptation, Ocular↗

PubMed2006

[The influence of IOL implantation on visual acuity, contrast sensitivity and colour vision 2 and 4 months after cataract surgery].

PURPOSE: To assess the change in visual acuity, contrast sensitivity and colour vision in relation to the time after cataract surgery and to the type of implanted IOL, and to compare visual functions by patients with one and two pseudophakic eyes. METHODS: 45 cataract patients were examined before and then 2 and 4 month after the cataract surgery. Visual acuity (VA) was tested on logMAR optotype chart with Landolt rings, contrast sensitivity (CS) was tested on the Pelli-Robson chart and the SWCT chart. For colour vision (CV) testing, the standard Farnsworth D-15 test and the desaturated Lanthony D-15 test were used. The patients were divided into two groups--a group with one pseudophakic eye and a group with two pseudophakic eyes, and also according to the type of IOL--PMMA or hydrophobic acrylate that had been implanted. Control group was composed of phakic subjects with no ocular pathology. RESULTS: After the cataract surgery, in both groups there was a significant improvement in monocular and binocular VA (p < 0.05), in monocular and binocular CS using both types of charts--Pelli-Robson (p < 0.05) and SWCT in all the spatial frequencies (p < 0.05). Also, a significant decrease in the number of minor errors in the standard Farnsworth D-15 test (p < 0.05) as well as a substantial decrease in the number of minor and major errors in the desaturated Lanthony D-15 test (p < 0.05) and an overall improvement of CV (p < 0.05) were detected. There was no difference between the results 2 and 4 month after the surgery, except for CS in 12 c/deg (p < 0.05). The patients with two pseudophakic eyes had postoperatively better binocular VA and CS in the spatial frequencies of 12 c/deg and 18 c/deg and attained postoperative values comparable to those of control subjects. No significant difference in VA, CS or CV was found between the PMMA and hydrophobic acrylate intraocular lenses. CONCLUSION: After the cataract surgery, the visual functions tested by means of psychophysical methods of VA, CS and CV significantly improve and are stable 2 month after the surgery. The second eye surgery improves binocular visual functions the level of which doesn't differ from that of normal phakic subjects. There was no influence of the type of IOL on final state of VA, CS or CV.

Aged↗

PubMed2001

Effect of chromatic aberration on contrast sensitivity in pseudophakic eyes.

OBJECTIVE: To evaluate the effect of chromatic aberrations in pseudophakic eyes with various types of intraocular lenses (IOLs). PATIENTS AND METHODS: The study included 51 eyes of 33 patients who underwent cataract surgery. The eyes were divided into 3 groups according to the material from which their IOL was made: group 1, polymethyl methacrylate; group 2, silicone; and group 3, an acrylate/methacrylate copolymer. Ten normal phakic control eyes (group 4) underwent the same examination. Best-corrected distance visual acuity and contrast sensitivity were measured under white light and monochromatic light with wavelengths of 470 nm, 549 nm, and 630 nm, with the best correction under white light. RESULTS: There were no significant differences in best-corrected visual acuity and contrast sensitivity under the 549-nm monochromatic light in any group. However, under both white multichromatic light and 470- and 630-nm monochromatic light, the mean contrast sensitivity in group 3 tended to be lower, sometimes significantly, than in the other IOL groups. CONCLUSIONS: Our results showed that longitudinal chromatic aberrations of some IOLs may degrade the quality of the retinal image. Attention must be paid to the detailed optical performance of IOL materials to achieve good visual function.

Acrylates↗

PubMed2005

Chromatic and luminance contrast sensitivities in asymptomatic carriers from a large Brazilian pedigree of 11778 Leber hereditary optic neuropathy.

PURPOSE: To determine whether asymptomatic 11778 LHON carriers demonstrated impairments in (1) chromatic red/green (R/G) and blue/yellow (B/Y) contrast sensitivity functions (CSF) and in (2) luminance contrast sensitivity functions in the spatial CSF (SCSF) and temporal CSF (TCSF) domains. METHODS: Twenty-five carriers (8 male, 17 female; 34.1 +/- 15.1 years of age) of homoplasmic 11778 LHON from the same well-described family and 30 age-matched controls (17 male, 13 female; 29.2 +/- 7.1 years of age) were tested in one eye, randomly selected. Of the 25 eyes tested, 18 had normal fundus, 5 had swelling and microangiopathy, and 2 had temporal pallor. The R/G and B/Y CSFs were obtained after equiluminance correction with bichromatic horizontal sinusoidal gratings at 0.3, 0.7, and 2 cycles per degree (cpd); the SCSFs were obtained with achromatic gratings at 0.3, 2, 6, and 12 cpd; and the TCSFs were obtained at 2, 10, 20, and 33 Hz with sinusoidal modulation of a 2.7 degrees field with a superimposed spatial Gabor function. RESULTS: Differences between carriers and controls were statistically significant for all spatial frequencies of chromatic and luminance SCSFs, but not for the TCSFs. R/G equiluminance settings of carriers differed from those of controls (P < 0.001), requiring higher luminance in the green; B/Y equiluminance settings were not statistically different in carriers and controls. Fundus findings did not correlate with CS results. CONCLUSIONS: Luminance and chromatic spatial CS losses that affected all tested spatial frequencies, are reported in LHON asymptomatic carriers with the mtDNA 11778 mutation. No losses were found in the temporal CSF. An intriguing finding is that the blue system is substantially spared in this LHON family. These represent subclinical visual impairments in otherwise asymptomatic LHON carriers.

Adolescent↗