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Showing papers on "Contrast (vision) published in 2009"


Journal ArticleDOI
TL;DR: The visual contrast sensitivity (the reciprocal of contrast threshold) was studied as a function of age and binocular and monocular contrast thresholds were made for normal observers at spatial frequencies within the range 0.5 to 40 cycles/degree.
Abstract: The visual contrast sensitivity (the reciprocal of contrast threshold) was studied as a function of age. Psychophysical measurements of binocular and monocular contrast thresholds were made for 33 normal observers at spatial frequencies within the range 0.5 to 40 cycles/degree. The observers were divided into three different age groups: young, middle-aged, and old subjects with the age ranges 6--10 years, 20--40 years, and 60--70 years, respectively. All observers had healthy eyes, normal vision, and Snellen visual acuity of 1.0 or better in both eyes. In all groups, contrast sensitivity for binocular and monocular viewing peaked at a spatial frequency around 3--5 cycles/degree and showed the typical attenuation at low and high spatial frequencies. The binocular contrast sensitivity was higher than the monocular. There was no significant difference between young and middle-aged subjects with regard to contrast sensitivity. Subjects aged 60 years or more showed significantly lower contrast sensitivity than younger subjects for most spatial frequencies above 4 cycles/degree. We may thus conclude that both the binocular and monocular contrast sensitivity seemed independent of age within the range of 6 to 40 years. For higher ages studied (above 60 years), there was a loss of sensitivity in the middle and high frequency regions.

245 citations


Journal ArticleDOI
TL;DR: It is reported that contrast sensitivity is quite different under laboratory than natural viewing conditions: adaptation or masking with natural scenes attenuates contrast sensitivity at low spatial and temporal frequencies, and results suggest that sensitivity to spatial structure in natural scenes depends on the distribution of local edges as well as the local amplitude spectrum.
Abstract: The contrast sensitivity function is routinely measured in the laboratory with sine-wave gratings presented on homogenous gray backgrounds; natural images are instead composed of a broad range of spatial and temporal structures. In order to extend channel-based models of visual processing to more natural conditions, we examined how contrast sensitivity varies with the context in which it is measured. We report that contrast sensitivity is quite different under laboratory than natural viewing conditions: adaptation or masking with natural scenes attenuates contrast sensitivity at low spatial and temporal frequencies. Expressed another way, viewing stimuli presented on homogenous screens overcomes chronic adaptation to the natural environment and causes a sharp, unnatural increase in sensitivity to low spatial and temporal frequencies. Consequently, the standard contrast sensitivity function is a poor indicator of sensitivity to structure in natural scenes. The magnitude of masking by natural scenes is relatively independent of local contrast but depends strongly on the density of edges even though neither greatly affects the local amplitude spectrum. These results suggest that sensitivity to spatial structure in natural scenes depends on the distribution of local edges as well as the local amplitude spectrum.

210 citations


Journal ArticleDOI
TL;DR: This motion contrast technique has demonstrated the ability to visualize resolution-limited vasculature independent of vessel orientation and flow velocity and to provide non-invasive vascular visualization comparable to currently used invasive angiographic imaging.
Abstract: Phase variance-based motion contrast imaging is demonstrated using a spectral domain optical coherence tomography system for the in vivo human retina. This contrast technique spatially identifies locations of motion within the retina primarily associated with vasculature. Histogram-based noise analysis of the motion contrast images was used to reduce the motion noise created by transverse eye motion. En face summation images created from the 3D motion contrast data are presented with segmentation of selected retinal layers to provide non-invasive vascular visualization comparable to currently used invasive angiographic imaging. This motion contrast technique has demonstrated the ability to visualize resolution-limited vasculature independent of vessel orientation and flow velocity.

188 citations


Journal ArticleDOI
TL;DR: Cross-modal cueing of attention boosted the apparent contrast of the visual target in association with an enlarged neural response in the contralateral visual cortex that began within 100 ms after target onset.
Abstract: The question of whether attention makes sensory impressions appear more intense has been a matter of debate for over a century. Recent psychophysical studies have reported that attention increases apparent contrast of visual stimuli, but the issue continues to be debated. We obtained converging neurophysiological evidence from human observers as they judged the relative contrast of visual stimuli presented to the left and right visual fields following a lateralized auditory cue. Cross-modal cueing of attention boosted the apparent contrast of the visual target in association with an enlarged neural response in the contralateral visual cortex that began within 100 ms after target onset. The magnitude of the enhanced neural response was positively correlated with perceptual reports of the cued target being higher in contrast. The results suggest that attention increases the perceived contrast of visual stimuli by boosting early sensory processing in the visual cortex.

161 citations


Journal ArticleDOI
TL;DR: The development of visual acuity and contrast sensitivity into childhood is discussed, with a focus on visual development of infants.

147 citations


Journal ArticleDOI
TL;DR: The findings clearly show that fearful facial expressions increases the amplitude of P1 and N170 in comparison to neutral faces but only in LSF faces, irrespective of contrast or luminance equalization, further suggesting that LSF information plays a crucial role in the early brain responses to fear.
Abstract: Rapidly decoding the emotional content of a face is an important skill for successful social behavior. Several Event Related brain Potential (ERP) have indicated that emotional expressions already influence brain activity as early as 100 ms. Some studies hypothesized that this early brain response to fear depends on coarse-magnocellular inputs, which are primarily driven by Low Spatial Frequency (LSF) cues. Until now however, evidence is inconclusive probably due to the divergent methods used to match luminance and contrast across spatial frequencies and emotional stimuli. In the present study, we measured ERPs to LSF and HSF faces with fearful or neutral expressions when contrast and luminance was matched across SF or not. Our findings clearly show that fearful facial expressions increases the amplitude of P1 (only for contrast–luminance equated images) and N170 in comparison to neutral faces but only in LSF faces, irrespective of contrast or luminance equalization, further suggesting that LSF information plays a crucial role in the early brain responses to fear. Furthermore, we found that, irrespective of luminance or contrast equalization, N170 occurred faster faster when perceiving LSF faces than HSF faces, again emphasizing the primacy of LSF processing in early face perception.

145 citations


Patent
22 Oct 2009
TL;DR: In an image processing method, extraction points are set inside the draw line as the region with less luminance change relative to the periphery, and extraction points on the background outside the drawline in a sample image such as a letter and a number.
Abstract: In an image processing method, extraction points are set inside the draw line as the region with less luminance change relative to the periphery, and extraction points are set on the background outside the draw line in a sample image such as a letter and a number. Pixel data of the extraction points are used to obtain the normalization correlation coefficient with respect to the target image in the determination region. As the template data are generated using pixel data of two groups of the extraction points with clear contrast in the luminance difference therebetween, the true image to be determined as being the same as the template image is detected accurately through the calculation for a short period of time.

135 citations


Journal ArticleDOI
TL;DR: The results show that chromatic edge contrast is an independent source of information that can be linearly combined with other cues for the proper segmentation of objects in natural and artificial vision systems.
Abstract: Form vision is traditionally regarded as processing primarily achromatic information. Previous investigations into the statistics of color and luminance in natural scenes have claimed that luminance and chromatic edges are not independent of each other and that any chromatic edge most likely occurs together with a luminance edge of similar strength. Here we computed the joint statistics of luminance and chromatic edges in over 700 calibrated color images from natural scenes. We found that isoluminant edges exist in natural scenes and were not rarer than pure luminance edges. Most edges combined luminance and chromatic information but to varying degrees such that luminance and chromatic edges were statistically independent of each other. Independence increased along successive stages of visual processing from cones via postreceptoral color-opponent channels to edges. The results show that chromatic edge contrast is an independent source of information that can be linearly combined with other cues for the proper segmentation of objects in natural and artificial vision systems. Color vision may have evolved in response to the natural scene statistics to gain access to this independent information.

119 citations


Journal ArticleDOI
TL;DR: It is shown that a major reason for this well-known contrast discrepancy lies in the neglect of the detector modulation-transfer function in image simulations.
Abstract: A fully quantitative approach to high-resolution transmission electron microscopy requires a satisfactory match between image simulations and experiments. While almost perfect agreement between simulations and experiments is routinely achieved on a relative contrast level, a huge mutual discrepancy in the absolute image contrast by a factor of 3 has been frequently reported. It is shown that a major reason for this well-known contrast discrepancy, which is often called Stobbs-factor problem, lies in the neglect of the detector modulation-transfer function in image simulations.

117 citations


Journal ArticleDOI
TL;DR: It is indicated that adjusting for contrast can increase the sensitivity of MR morphometry to variables of interest, particularly in areas earlier reported to be compromised in AD.

109 citations


BookDOI
01 Jan 2009
TL;DR: A.L. Gilchrist, Absolute Versus Relative Theories of Lightness Perception as mentioned in this paper, The Psychophysics of Contrast Brightness, and Contrasting Brightness and Ordinary Seeing.
Abstract: Contents: A.L. Gilchrist, Absolute Versus Relative Theories of Lightness Perception. P. Whittle, The Psychophysics of Contrast Brightness. P. Whittle, Contrast Brightness and Ordinary Seeing. L. Arend, Surface Colors, Illumination, and Surface Geometry: Intrinsic-Image Models of Human Color Perception. W. Gerbino, Achromatic Transparency. S.S. Bergstrom, Color Constancy: Arguments for a Vector Model for the Perception of Illumination, Color, and Depth.

Journal ArticleDOI
TL;DR: Patients with relatively well conserved visual acuity showed a marked impairment in contrast sensitivity for targets of high and intermediate spatial frequencies, while patients with more advanced disease showed a pronounced impairment across a larger spectrum of frequencies.
Abstract: Psychophysical measurements of contrast thresholds for sinusoidal gratings of variable frequency were made in normal controls and in patients with macular disease. Normal controls showed a U-shaped contrast sensitivity function comparable with previous reports. Patients with relatively well conserved visual acuity showed a marked impairment in contrast sensitivity for targets of high and intermediate spatial frequencies, while patients with more advanced disease showed a pronounced impairment across a larger spectrum of frequencies. Our findings provide insight into the visual difficulties of daily life of patients with macular disease. The determination of contrast sensitivity seems to be an important and very sensitive tool for the detection of early disturbances.

Journal ArticleDOI
TL;DR: In this paper, the authors proposed a method to enhance the image quality for a given backlight intensity by performing brightness compensation and local contrast enhancement, where global image statistics and backlight level are considered to maintain the overall brightness of the image.
Abstract: One common way to extend the battery life of a portable device is to reduce the LCD backlight intensity. In contrast to previous approaches that minimize the power consumption by adjusting the backlight intensity frame by frame to reach a specified image quality, the proposed method optimizes the image quality for a given backlight intensity. Image is enhanced by performing brightness compensation and local contrast enhancement. For brightness compensation, global image statistics and backlight level are considered to maintain the overall brightness of the image. For contrast enhancement, the local contrast property of human visual system (HVS) is exploited to enhance the local image details. In addition, a brightness prediction scheme is proposed to speed up the algorithm for display of video sequences. Experimental results are presented to show the performance of the algorithm.

Journal ArticleDOI
TL;DR: Pattern-VER and visual field examinations are sensitive tests to detect early toxicity and together with OCT, they may help to identify patients who are likely to develop clinical toxicity.
Abstract: Aim: The aim of the study was to evaluate various visual parameters for early detection of ethambutol toxicity. Method: This was a prospective study of 104 eyes of 52 patients being treated with ethambutol in the Directly Observed Treatment Strategy Centre (Dr R P Centre for Opthalmic Sciences, New Delhi, India). Visual acuity, visual fields, visual evoked responses (VER), stereoacuity and retinal nerve fibre layer (RNFL) thickness on optical coherence tomography (OCT) were assessed. Examinations were done before the start of therapy, after 1 and 2 months of treatment, and 1 month after stopping ethambutol. Results: No visual functional defect was noted at baseline. On follow-up, visual acuity, colour vision, contrast sensitivity, fundus and stereoacuity were not affected in any patient. Visual field defects developed in 7.69% (8/104) of the eyes. Pattern-VER showed an increased mean latency of the P 100 wave after 1 and 2 months of therapy (p Conclusion: Pattern-VER and visual field examinations are sensitive tests to detect early toxicity. Together with OCT, they may help to identify patients who are likely to develop clinical toxicity.

Journal ArticleDOI
TL;DR: The aspheric IOL provided good functional vision at far and near, with lower performance at intermediate distance; good photopic contrast sensitivity and lower mesopic performance; and a low incidence of visual disturbances.
Abstract: Purpose To evaluate distance, intermediate, and near vision after bifocal aspheric AcrySof ReSTOR SN6AD1 intraocular lens (IOL) implantation. Setting Fernandez-Vega Ophthalmological Institute, Oviedo, Spain. Methods Binocular distance best corrected visual acuity (BCVA) (4.0 m), best distance-corrected near (40.0 cm) and intermediate (70.0, 60.0, 50.0 cm) acuities, and contrast sensitivity under photopic (85.0 candelas [cd]/m 2 ) and mesopic (3.0 cd/m 2 ) conditions with and without glare were measured postoperatively. A patient-satisfaction and visual phenomena questionnaire was administered. Results Six months postoperatively, the mean acuities (logMAR) were binocular BCVA, −0.064 ± 0.049 (SD); best corrected near, −0.041 ± 0.061; best corrected intermediate, 0.147 ± 0.130 (70.0 cm), 0.036 ± 0.133 (60.0 cm), and −0.126 ± 0.077 (50.0 cm). The BCVA and best corrected near acuity were 20/25 or better in all patients. Through-focus binocular logMAR acuities had 2 peaks at the expected far focus and near focus (0.00 diopter [D] and −2.40 D, respectively), with somewhat reduced acuity (20/32) at intermediate distances. Photopic contrast sensitivity was within the standard normal range. Mesopic contrast sensitivity was lower than under photopic conditions, particularly at higher spatial frequencies. Patients reported good performance for distance, near, and intermediate visual tasks with no or minimal difficulty with specific tasks. No patient reported severe visual phenomena; halos and glare were rated as none to moderate. Conclusions The aspheric IOL provided good functional vision at far and near, with lower performance at intermediate distance; good photopic contrast sensitivity and lower mesopic performance; and a low incidence of visual disturbances.

Journal ArticleDOI
TL;DR: In this paper, the authors assessed the postural stability and gait characteristics of adults with age-related maculopathy and identified the visual factors associated with postural stabilisation.
Abstract: PURPOSE. To assess the postural stability and gait characteristics of adults with age-related maculopathy (ARM) and to identify the visual factors associated with postural stability and gait in this clinical population. METHODS. Participants included 80 individuals with a range of severity of ARM (mean age, 77.2 years). Binocular visual function measures included visual acuity, contrast sensitivity, and merged binocular visual fields. Postural stability was assessed on both a firm and a foam surface using center-of-pressure measures derived from a force platform. Forty three of the participants underwent a three-dimensional motion analysis to quantify gait characteristics, including walking velocity, proportion of time spent with both feet in contact with the ground (double-support time), stride length, and step width. RESULTS. After adjustment for age, sex, self-reported physical function, and cataract severity, all the vision measures were significantly associated with postural stability on the foam surface, with contrast sensitivity being the strongest correlate. In the analysis of the gait measures, only contrast sensitivity was significantly associated with walking velocity, step width, or stride length, whereas contrast sensitivity and visual field loss were both significantly associated with double-support time. CONCLUSIONS. Impaired contrast sensitivity was associated with postural instability, slower walking velocity, increased step width, and reduced stride length. Impairments in either contrast sensitivity or visual fields were associated with increased double-support time. This result suggests that loss of contrast sensitivity and visual fields in patients with ARM can lead to balance and mobility problems.

Journal ArticleDOI
TL;DR: Both visual acuity and contrast sensitivity measurements are useful in the evaluation of the nature of visual impairment due to diabetic eye disease.
Abstract: Spatial contrast sensitivity of 19 diabetics with different degrees of visual impairment was studied. It was found that contrast sensitivity at intermediate and low spatial frequencies may decrease without corresponding loss of visual acuity. In advanced cases of diabetes the opposite may be true: contrast sensitivity was better than expected on the basis of visual acuity. Thus both visual acuity and contrast sensitivity measurements are useful in the evaluation of the nature of visual impairment due to diabetic eye disease.

Journal ArticleDOI
TL;DR: The objective is to study the relationship between lens opacity and intraocular straylight, visual acuity and contrast sensitivity, and to establish a baseline for this type of research.
Abstract: PURPOSE: To study the relationship between lens opacity and intraocular straylight, visual acuity and contrast sensitivity. METHODS: We investigated 2422 drivers in five clinics in different European Union (EU) member states aged between 20 and 89 years as part of a European study into the prevalence of visual function disorders in drivers. We measured visual acuity [Early Treatment Diabetic Retinopathy Study (ETDRS) chart], contrast sensitivity (Pelli-Robson chart) and intraocular straylight (computerized straylight meter). Lens opacities were graded with the Lens Opacities Classification System III (LOCS) without pupillary dilation. Participants answered the National Eye Institute Visual Functioning Questionnaire - 25. RESULTS: Intraocular straylight was related more strongly to LOCS score than to both visual acuity and contrast sensitivity. Visual acuity and contrast sensitivity were correlated to each other well, but to intraocular straylight to a much lesser extent. Self-reported visual quality was best related to contrast sensitivity; night driving difficulty was best related to visual acuity. CONCLUSION: Straylight is found to have added value for visual function assessment in drivers, whereas if visual acuity is known contrast sensitivity has limited added value. Language: en

Journal ArticleDOI
TL;DR: The majority of mimics closely resembled models in terms of color and luminance from a nonsubjective perspective, but fish that have potentially trichromatic visual systems with ultraviolet sensitivity had a much better capacity to discriminate between models and mimics compared with fish with midrange sensitivity or dichromatic (2 cone photoreceptors) fish.
Abstract: Batesian and aggressive mimics are considered to be under selective pressure to resemble their models, whereas signal receivers are under selection to discriminate between mimics and models. However, the perceptual ability of signal receivers to discriminate between mimics and models is rarely studied. Here we examined 15 model-mimic coral reef fish pairs using nonsubjective methods to judge the accuracy of mimics in terms of color and luminance. We then investigated the potential ability of fish with various visual systems to discriminate between model and mimic colors using theoretical vision models. We found the majority of mimics closely resembled models in terms of color and luminance from a nonsubjective perspective. However, fish that have potentially trichromatic (3 distinct cone photoreceptors) visual systems with ultraviolet sensitivity had a much better capacity to discriminate between models and mimics compared with fish with midrange sensitivity or dichromatic (2 cone photoreceptors) fish. The spectral reflectance of color patches reflected by models and mimics became more similar with an increase in depth, indicating that signal receivers may be more likely to distinguish mimics from models in habitats located closer to the surface. There was no such change in luminance contrast with depth. The selection pressure on mimics to accurately resemble their model is therefore predicted to vary depending on the visual system of the signal receiver and the light environment.

Journal ArticleDOI
TL;DR: The results offer a unifying explanation for disparate studies and suggest that deficits in early sensory gain affect subsequent integrative processes.
Abstract: Deficits in early visual processing are well documented in schizophrenia, using methods such as contrast sensitivity. Higher, integrative stages of functioning, such as susceptibility to visual illusions, have been evaluated less extensively. For example, patients show increased susceptibility to (ie, are more easily affected by) the Muller-Lyer illusion but decreased susceptibility (ie, are less easily affected by) to stereopsis based upon binocular disparity. The basis for pattern of illusion response and interaction between sensory and integrative stages of processing, however, is unclear. We tested a group of 38 patients and 28 control subjects in contrast sensitivity, the Muller-Lyer and Poggendorff illusions, as well as a subgroup in stereopsis and the Ponzo illusion, Sander parallelogram, and Hermann grid illusions. We predicted that patients would be more susceptible to tests that become more apparent with increased contrast (Muller-Lyer illusion), less susceptible to tests that become less apparent with increased contrast (stereopsis, Ponzo illusion, Hermann grid), and equally susceptible to contrast-insensitive tests (Poggendorff illusion). Additionally, the Hermann grid was tested at varying levels of contrast. Patients demonstrated significant deficits in contrast sensitivity, especially to brief, low spatial frequency stimuli, and the predicted differential response to the tested illusions. Additionally, poor performance on stereopsis and the Hermann grid significantly correlated with decreased contrast sensitivity (all P's <.01). Muller-Lyer illusion and stereopsis performance were also inversely related (P < .01). This study replicates and expands upon previous findings with visual illusions. Our results offer a unifying explanation for disparate studies and suggest that deficits in early sensory gain affect subsequent integrative processes.

Journal ArticleDOI
TL;DR: Normal central and peripheral contrast sensitivity is determined in 10 subjects 61–71 years‐old, to serve as a basis for the glaucoma studies, and it is confirmed that contrast sensitivity was higher for dynamic than for static presentation of gratings of low spatial frequencies both centrally and peripherally.
Abstract: Contrast sensitivity for moving and stationary sine grating patterns was determined in central and peripheral parts of the visual field. The method was primarily developed as a possible screening procedure for visual defects in glaucoma. Contrast sensitivity to moving patterns seemed maximal both in central and in 10 degrees of eccentric viewing for square wave reversals of temporal frequencies 0.5-5 Hz. We selected 2Hz for the clinical procedure. Further, we have determined normal central and peripheral contrast sensitivity in 10 subjects 61-71 years-old, to serve as a basis for the glaucoma studies. We used this age group since glaucoma mainly affects elderly people. We confirmed that contrast sensitivity was higher for dynamic than for static presentation of gratings of low spatial frequencies (below 1 c/d) both centrally and peripherally. For patterns of medium or high spatial frequencies, dynamic and static stimuli were equally detectable. The absolute level of contrast sensitivity was higher centrally than peripherally in the interval 0.3-4 c/d. The lower visual hemifield exhibited greater sensitivity, for both static and dynamic gratings, than the upper one.

Journal ArticleDOI
TL;DR: The diffractive multifocal intraocular lens with a low add power provided significantly better intermediate and near visual acuity than the monofocal IOL, and all‐distance visual AcrySof IQ was independent of pupil diameter and IOL displacement.
Abstract: Purpose To compare visual acuity from far to near, contrast visual acuity, and acuity in the presence of glare (glare visual acuity) between an aspheric diffractive multifocal intraocular lens (IOL) with a low addition (add) power (+3.0 diopters) and a monofocal IOL. Setting Hayashi Eye Hospital, Fukuoka, Japan. Methods This prospective study comprised patients having implantation of an aspheric diffractive multifocal ReSTOR SN6AD1 IOL with a +3.0 D add (multifocal group) or a monofocal AcrySof IQ SN60WF IOL (monofocal group). Visual acuity from far to near distances, contrast acuity, and glare acuity were evaluated 3 months postoperatively. Results Each IOL group comprised 64 eyes of 32 patients. For monocular and binocular visual acuity, the mean uncorrected and distance-corrected intermediate acuity at 0.5 m and the near acuity at 0.3 m were significantly better in the multifocal group than in the monofocal group (P≤.0035); distance and intermediate acuity at 0.7 m and 1.0 m were similar between the 2 groups. No significant differences were observed between groups in contrast acuity and glare acuity under photopic and mesopic conditions. Furthermore, no significant correlation was found between all-distance acuity and pupil diameter or between visual acuity and IOL decentration and tilt. Conclusions The diffractive multifocal IOL with a low add power provided significantly better intermediate and near visual acuity than the monofocal IOL. Contrast sensitivity with and without glare was reduced with the multifocal IOL, and all-distance visual acuity was independent of pupil diameter and IOL displacement.

Journal ArticleDOI
TL;DR: In this paper, the spatial contrast sensitivity function (CSF) and grating acuity were measured in two barn owls with psychophysical techniques, and the CSF found here renders the typical band-limited, inverted U-shaped function, with a low maximum contrast sensitivity of 8-19 at a spatial frequency of 1 cyc/deg.
Abstract: The eyes of barn owls (Tyto alba pratincola) display very little aberrations, and have thus excellent optical quality. In a series of behavioral experiments, we tested whether this presumably beneficial feature is also reflected at a perceptual level in this species. As fundamental indicators for visual performance, the spatial contrast sensitivity function (CSF) and grating acuity were measured in two barn owls with psychophysical techniques. Stimulus luminance was 2.7 cd/m(2). The CSF found here renders the typical band-limited, inverted U-shaped function, with a low maximum contrast sensitivity of 8-19 at a spatial frequency of 1 cyc/deg. Grating acuity was estimated from the CSF high frequency cut-off and yielded 3.0-3.7 cyc/deg. In a second experiment, in which contrast was held constant and spatial frequency was varied, grating acuity was measured directly (2.6-4.0 cyc/deg). These results put barn owls at the very low end of the visual acuity spectrum of birds, and demonstrate that visual resolution and sensitivity cannot be predicted by optical considerations alone.

Journal ArticleDOI
TL;DR: Contrast thresholds were continuously recorded in six points of the visual field through a repetitive up-and-down staircase method using the automatic perimeter developed by Heijl & Krakau (1975b), finding a decreased contrast sensitivity with increasing test time.
Abstract: Contrast thresholds were continuously recorded in six points of the visual field through a repetitive up-and-down staircase method using the automatic perimeter developed by Heijl & Krakau (1975b). The uninterrupted sessions lasted about 30 min. Nineteen patients with a verified diagnosis of glaucoma, or in whom glaucoma was suspected, and twelve healthy normal subjects were tested. With increasing test time, a decreased contrast sensitivity was found. In most subjects the mean threshold increment was small (less than 1.5 dB). The threshold increments were larger in the patient group than in the normal subjects--many test points showing increments of 6-10 dB during the test session. Such a large deterioration of sensitivity was most common in eyes with visual field defects. Test points which showed large threshold increments were often situated in the vicinity of documented visual field defects. In eyes with pathological visual fields, the short-term variation increased with increasing test time. An impairment of fixation with increasing test time was found in the patient group.

Journal ArticleDOI
TL;DR: This study shows that blue-light-filtering IOLs negatively affect contrast acuity and blue/yellow foveal threshold when compared with UV- Filtering Iols, and suggests bilateral implantation of the same IOL type and avoidance of a mixed implantation in patients with high demands in color vision.

Journal ArticleDOI
TL;DR: Current research into visual hallucination is predominantly ophthalmology-led, with increasing recognition of the phenomena, their prevalence and prognosis within the specialty, and whether hallucinations require treatment and, if so, what that treatment should be remains unclear.
Abstract: Purpose of reviewThe literature related to visual hallucinations in ophthalmological settings from 2007 to 2008 is presented as a review of recent developments and trends.Recent findingsAcuity, contrast sensitivity, age and sex emerge as significant and consistent risk factors for visual hallucinati

Journal ArticleDOI
TL;DR: Determination of the contrast sensitivity function seems to be an additional tool besides acuity measurements to document changes of visual function during treatment of amblyopia to indicate that the abnormalities in spatial vision are different in amblyopic due to strabismus or anisometropia during childhood.
Abstract: The contrast threshold of sinusoidal gratings of varying contrast and frequency was examined in children with amblyopia due to strabismus or anisometropia. In strabismic amblyopia the contrast sensitivity is depressed for only a limited band of high spatial frequencies. In anisometropic amblyopia depression of the contrast sensitivity function (CSF) was found over the whole frequency range. The CSF could not be predicted from the visual acuity measurements in amblyopic eyes due to strabismus, whereas a rough correlation was observed in anisometropia. During occlusion treatment of the dominant eye in anisometropia the visual acuity and the contrast sensitivity function of the amblyopic eye improved in parallel. The study indicates that the abnormalities in spatial vision are different in amblyopia due to strabismus or anisometropia during childhood. Determination of the contrast sensitivity function seems to be an additional tool besides acuity measurements to document changes of visual function during treatment of amblyopia.

Journal ArticleDOI
TL;DR: Close-loop adaptive optics is used to test the visual benefit of correcting monochromatic high-order aberrations on spatial vision for observers ranging in age from 18 to 81 years, indicating a larger role of additional optical factors when the impact of HOAs is removed and lending support for the importance of neural factors in age-related changes in spatial vision.
Abstract: The contributions of optical and neural factors to age-related losses in spatial vision are not fully understood. We used closed-loop adaptive optics to test the visual benefit of correcting monochromatic high-order aberrations (HOAs) on spatial vision for observers ranging in age from 18 to 81 years. Contrast sensitivity was measured monocularly using a two-alternative forced-choice (2AFC) procedure for sinusoidal gratings over 6 mm and 3 mm pupil diameters. Visual acuity was measured using a spatial 4AFC procedure. Over a 6 mm pupil, young observers showed a large benefit of AO at high spatial frequencies, whereas older observers exhibited the greatest benefit at middle spatial frequencies, plus a significantly larger increase in visual acuity. When age-related miosis is controlled, young and old observers exhibited a similar benefit of AO for spatial vision. An increase in HOAs cannot account for the complete senescent decline in spatial vision. These results may indicate a larger role of additional optical factors when the impact of HOAs is removed, but also lend support for the importance of neural factors in age-related changes in spatial vision.

Journal ArticleDOI
TL;DR: This work examines the first stage of visual processing – sampling by the ommatidial array – in the compound eye of the fiddler crab Uca vomeris and reveals five distinct eye regions which exhibit clear differences in the organisation of the local sampling array.
Abstract: Given the great range of visual systems, tasks and habitats, there is surprisingly little experimental evidence of how visual limitations affect behavioural strategies under natural conditions. Analysing this relationship will require an experimental system that allows for the synchronous measurement of visual cues and visually guided behaviour. The first step in quantifying visual cues from an animal's perspective is to understand the filter properties of its visual system. We examined the first stage of visual processing - sampling by the ommatidial array - in the compound eye of the fiddler crab Uca vomeris. Using an in vivo pseudopupil method we determined sizes and viewing directions of ommatidia and created a complete eye map of optical and sampling resolution across the visual field. Our results reveal five distinct eye regions (ventral, dorsal, frontal, lateral and medial) which exhibit clear differences in the organisation of the local sampling array, in particular with respect to the balance of resolution and contrast sensitivity. We argue that, under global eye space constraints, these regional optimisations reflect the information content and behavioural relevance of the corresponding parts of the visual field. In demonstrating the tight link between visual sampling, visual cues and behavioural strategies, our analysis highlights how the study of natural behaviour and natural stimuli is essential to our understanding and interpretation of the evolution and ecology of animal behaviour and the design of sensory systems.

Journal ArticleDOI
TL;DR: The spatial contrast threshold for a sinusoidal grating of varying contrast and frequency generated with a small‐field or a large‐field TV‐display was examined in normal subjects and in patients with macular disorders.
Abstract: The spatial contrast threshold for a sinusoidal grating of varying contrast and frequency generated with a small-field or a large-field TV-display was examined in normal subjects and in patients with macular disorders. Impairment of contrast sensitivity (reciprocal of contrast) was observed in the different maculopathies investigated. Attenuation of the high- and middle-frequency ranges was an early finding in macular disease, whereas changes including the low-frequency range was observed in more advanced maculopathies. Comparison of results obtained using the small (1.4 degree) or large-field (6 degree--24 degree) TV-system demonstrated a field-dependence of the contrast sensitivity attenuation in localized macular disorders. In more wide-spread lesions in the posterior pole, a contrast attenuation over the whole frequency range was found also with the largest (24 degree) stimulation field used. The study of the contrast sensitivity function supplements the traditional acuity measurements in quantifying the visual loss for objects larger than the resolution limit. I conclude that contrast threshold measurements are not only useful for describing visual loss, but also for tracking progression or recovery. The findings provide some additional insight into the visual difficulties of daily life of patients with a macular disorder. However, the definite role of contrast sensitivity measurements for diagnosing different visual disorders is still lacking.