Showing papers on "Contrast (vision) published in 1998"

Visual impairment and falls in older adults: the Blue Mountains Eye Study.

Abstract: OBJECTIVES: To examine the association between visual impairment and falls in older people. DESIGN: Cross-sectional survey of eye disease with retrospective collection of falls data. SETTING: Two postcode areas in the Blue Mountains west of Sydney, Australia. PARTICIPANTS: All people 49 years of age and older were invited to participate, 3654 (82.4%) of 4433 eligible residents took part, and 3299 answered questions about falls. MEASUREMENTS: Subjects had a detailed eye examination and answered questions about health and vision status, use of medication, and number of falls in the previous 12 months. RESULTS: Tests of visual function that had a statistically significant association with two or more falls after adjustment for confounders were visual acuity (prevalence ratio (PR) 1.9 for visual acuity worse than 20/30), contrast sensitivity (PR 1.2 for a 1-unit decrease at 6 cycles per degree), and suprathreshold visual field screening (PR 1.5 for 5 or more points missing). However, only visual acuity and contrast sensitivity were significantly associated with two or more falls per 1 standard deviation decrease. The presence of posterior subcapsular cataract (PR 2.1) and use of nonmiotic glaucoma medication (PR 2.0) had a statistically significant association with two or more falls; presence of age-related macular degeneration, diabetic retinopathy, and cortical or nuclear cataract did not. CONCLUSION: Visual impairment is strongly associated with two or more falls in older adults. In addition to poor visual acuity, visual factors such as reduced visual field, impaired contrast sensitivity, and the presence of cataract may explain this association.

Color and luminance information in natural scenes

Abstract: The spatial filtering applied by the human visual system appears to be low pass for chromatic stimuli and band pass for luminance stimuli. Here we explore whether this observed difference in contrast sensitivity reflects a real difference in the components of chrominance and luminance in natural scenes. For this purpose a digital set of 29 hyperspectral images of natural scenes was acquired and its spatial frequency content analyzed in terms of chrominance and luminance defined according to existing models of the human cone responses and visual signal processing. The statistical 1/f amplitude spatial-frequency distribution is confirmed for a variety of chromatic conditions across the visible spectrum. Our analysis suggests that natural scenes are relatively rich in high-spatial-frequency chrominance information that does not appear to be transmitted by the human visual system. This result is unlikely to have arisen from errors in the original measurements. Several reasons may combine to explain a failure to transmit high-spatial-frequency chrominance: (a) its minor importance for primate visual tasks, (b) its removal by filtering applied to compensate for chromatic aberration of the eye's optics, and (c) a biological bottleneck blocking its transmission. In addition, we graphically compare the ratios of luminance to chrominance measured by our hyperspectral camera and those measured psychophysically over an equivalent spatial-frequency range.

Visual features that vary together over time group together over space

Abstract: The visual system perceives objects as coherent even when some parts are hidden or discontinuous. How this representation is constructed from local features of many nearby objects is termed the 'binding problem.' Here we manipulate contrast in several drifting gratings that can be perceived as either independent objects or parts of a single object. Contrast modulations that are correlated in time enhance perceptual coherence, whereas uncorrelated modulations impair coherence. Presumably, correlated contrast modulations produce correlated responses in cortical neurons. Therefore, our results are consistent with the hypothesis that temporal correlation of neural activity is important for feature binding.

Poor visual discrimination and visual hallucinations in Parkinson's disease.

Abstract: This study examined the relationship between deficits in color and contrast discrimination and visual hallucinations (VH) in patients with Parkinson's disease (PD) and normal visual acuity. Thirty-five nondemented and nonpsychotic PD patients with normal visual acuity and without major ophthalmologic disease were interviewed twice and divided into two groups: hallucinators (n = 14) and non-hallucinating controls (n = 21). The groups were compared for color vision (assessed by Lanthony D-15 [LD] and Farnsworth-Munsell 100 hue [FM] tests), and for contrast sensitivity (tested by Vis tech tables [VT] and monocular and binocular Pelli-Robson test [PR]). There was no difference in age, duration or stage of PD, or dosage or duration of levodopa therapy between the two groups. Parkinson's disease patients showed impairment on all visual tests, with the hallucinators performing worse than the controls on all tests. This difference was significant for the LD (p < 0.007), the VT at 1.5 and 3 cycles per degree (p < 0.037 and 0.043, respectively) and the monocular PR tests (p < 0.049). The results led the authors to conclude that in patients with normal visual acuity, those with VH show added visual deficits of color and contrast discrimination. These ophthalmopathies may therefore be facilitating factors for visual hallucinations in PD and justify more focused research on the pathophysiology of visual hallucinations in Parkinson's disease.

Assessment of visual function in idiopathic intracranial hypertension: A prospective study

Abstract: The visual function of 35 patients with a diagnosis of idiopathic intracranial hypertension was assessed prospectively over a 3 year period. In assessing the visual function of cases of idiopathic intracranial hypertension a number of tests were employed including visual field assessment with Humphrey and Goldmann perimeters and documentation of visual acuity and contrast sensitivity. Loss of visual function is the only serious complication and may occur early or late in the course of the condition. An appropriate and sensitive clinical assessment regime is therefore of importance in the outpatient situation. Visual field assessment was documented as the most sensitive to detection of visual loss, with statistically greater sensitivity in comparison with visual acuity and contrast sensitivity testing. Detection of asymptomatic visual loss indicates the necessity for visual monitoring to ensure detection of insidious visual loss. The types of visual field defects noted in this study were typical of anterior optic nerve pathology of raised intracranial pressure and commonly included arcuate defects, nasal steps and global constriction. Visual loss was noted at presentation and during follow-up in up to 87% of patients using Goldmann perimetry and up to 82% of patients using Humphrey perimetry. The visual status improved significantly throughout the follow-up period and the final visual outcome was excellent or good in 83% of patients.

Visual correlates of mobility in real world settings in older adults with low vision

Abstract: :Purpose.To determine the effects of reducing light level from photopic to mesopic on performance of real world mobility tasks and how performance of these tasks relates to measures of visual sensory and perceptual function.Methods.The visual functions, acuity, peak letter contrast sensitivi

The Visible Differences Predictor: applications to global illumination problems

Abstract: In this study of global illumination computations, we investigate the applications of the perceptually-based Visual Difference Predictor (VDP) developed by Daly [5]. First, we validate the performance of this predictor in shadow masking by texture and luminance contrast experiments. We also experiment with Contrast Sensitivity Functions (CSFs) derived from the results of various psychophysical experiments, various spatial frequency and orientation channel decomposition schemes, and contrast definitions, in order to check predictor integrity and sensitivity to differing models of visual mechanisms. We show applications of the VDP to monitor the perceived quality of the progressive radiosity and Monte Carlo solutions, and decide upon their stopping conditions. Also, based on the local error metric provided by the predictor we show some initial attempts to drive adaptive mesh subdivision in radiosity computations.

A Comparison of Seven Visual Fatigue Assessment Techniques In Three Data-Acquisition VDT Tasks:

Abstract: We compared 7 methods of measuring visual fatigue--accommodation power, visual acuity, pupil diameter, critical fusion frequency (CFF), eye movement velocity, subjective rating of visual fatigue, and task performance--for their sensitivity to visual load. In the experiment, 10 participants performed a monitoring task at 2 viewing distances, read articles under 2 levels of screen contrast, and tracked visual targets at 2 different speeds. The same measurement techniques, excluding pupil diameter and eye movement velocity, were compared by extending the task time from 20 to 60 min with the same VDT tasks to test for possible improvement in sensitivity. The results indicated that sensitivities of accommodation power, visual acuity, and CFF were greatly improved by a longer task period, but these 3 measurement techniques did not distinguish among tasks. Pupil diameter, eye movement velocity, and subjective rating of visual fatigue were sensitive in differentiating tracking from reading and monitoring tasks. Eye movement velocity and subjective rating were sensitive to the changes in target velocity of the tracking task. Although task performance was not directly comparable to other measurement techniques, it helped to ensure that participants maintained the same performance level by devoting more resources to the high-load conditions. Actual or potential applications of this research include using some of these assessment techniques for the design of adaptive displays.

Spatial attention: effect of position uncertainty and number of distractor patterns on the threshold-versus-contrast function for contrast discrimination

Abstract: Our goal is to integrate knowledge about contrast discrimination with knowledge about spatial attention effects. An experiment is described that measures the effects of position uncertainty, number of distractors, and contrast on the contrast discrimination threshold in a fully crossed factorial design. The threshold-versus-contrast function is nonmonotonic in all conditions, decreasing and then increasing as contrast increases. Increasing uncertainty and/or the number of distractors increases thresholds, and there are interactions among the three variables indicating that uncertainty and distractor number have different effects on detection as distractor contrast varies. The results are well accounted for by a model that combines a nonlinear excitation/divisive inhibition model of pattern mechanisms with a noise-limited model of the decision process.

Contrast sensitivity and glare disability with diffractive and refractive multifocal intraocular lenses.

Abstract: Purpose: To compare contrast sensitivity and glare disability provided by diffractive and refractive multifocal intraocular lenses (IOLs). Setting: University Eye Clinic Vienna, Austria. Method: This study evaluated the contrast sensitivity and glare disability in 29 eyes with a diffractive multifocal IOL (3M815LE) and 12 with a three-piece, five-zone refractive multifocal IOL (AMC Array SSM 26 NB). The Brightness Acuity Tester (Mentor, Inc.) was used with stationary sinusoidal gratings at spatial frequencies of 0.5, 1, 3, 6, 11.4, and 22.8 cycles per degree (cpd) generated on a television monitor (Nicolet CS 2000). Results: The contrast sensitivity functions of both multifocal IOL groups were within the reference range and were identical at 0.5, 1, and 22.8 cpd spatial frequencies. At 3, 6, and 11.4 cpd, the contrast sensitivity function in the diffractive IOL group was 6, 9, and 10% lower than in the refractive IOL group, and the difference between groups was statistically significant at 6 cpd. When glare was present, contrast sensitivity in the diffractive IOL group was generally in the lower limit of the reference range and remained below at 3 and 6 cpd. Contrast sensitivity in the refractive IOL group remained below the reference range at 3 cpd. At 0.5 and 1 cpd, there were no differences between the groups. At the middle and high spatial frequencies (3, 6, 11.4, 22.8 cpd), contrast sensitivity in the diffractive group was 8, 16, 11, and 12% lower than in the refractive group. At 6 cpd, the between-group difference was statistically significant. Conclusion: Diffractive multifocal IOLs provided decreased contrast sensitivity and greater glare disability than refractive multifocal IOLs.

Seeing Beyond Retinopathy in Diabetes: Electrophysiological and Psychophysical Abnormalities and Alterations in Vision

Abstract: Contrast sensitivity testing, in common with color vision (another test of psychophysical function), demonstrates significant changes in diabetic subjects compared with nondiabetic controls, and there is some evidence for a relationship with grade of retinopathy. Changes in contrast sensitivity have been demonstrated in children and adults with diabetes of short duration, and some evidence exists for a correlation with poor glycemic control, although prospective studies are required to assess this relationship over a longer time period. Although both color vision and contrast sensitivity demonstrate similar patterns, studies that directly compare the two tests suggest that measurement of contrast sensitivity is the more sensitive and specific.

The selective impairment of the perception of first-order motion by unilateral cortical brain damage.

Abstract: First-order (Fourier) motion consists of stable spatiotemporal luminance variations. Second-order (non-Fourier) motion consists instead of spatiotemporal modulation of contrast, flicker, or spatial frequency. In spite of extensive psychophysical and computational analysis of the nature and relationship of these two types of motion, it remains unclear whether they are detected by the same mechanism or whether separate mechanisms are involved. Here we report the selective impairment of first-order motion, on a range of local and global motion tasks, in the contralateral visual hemifield of a patient with unilateral brain damage centered on putative visual areas V2 and V3 in the medial part of the occipital lobe. His perception of second-order motion was unimpaired. As his disorder is the obverse of that reported after damage in the vicinity of human visual area MT (V5), the results support models of motion processing in which first- and second-order motion are, at least in part, computed separately at the extrastriate cortical level.

Effect of Luminance Contrast on BOLD fMRI Response in Human Primary Visual Areas

Abstract: Goodyear, Bradley G. and Ravi S. Menon. Effect of luminance contrast on BOLD fMRI response in human primary visual areas. J. Neurophysiol. 79: 2204–2207, 1998. In this study, we examined the effect...

The angular range of achromatic target detection by honey bees

Abstract: Honeybees Apis mellifera were trained to enter a Y-maze and choose the arm with a rewarded disc presented against a grey background. The alternative arm displayed the unrewarded grey background alone. Training and testing were performed with the rewarding disc subtending different visual angles. The training disc was either achromatic and provided green contrast, or chromatic and provided the same amount of green contrast as the achromatic one. The bee-achromatic disc could be learned and detected by the bees whenever it subtended 5° or 10°, but not if it subtended 30°. The chromatic disc was learned well and detected at all three visual angles. However, at 5° the maximum level of correct choices was ca. 75% with the achromatic disc whilst it was ca. 90% with the chromatic one. Thus, the presence of chromatic contrast enhances considerably the level of correct choices for the same amount of green contrast. The lower threshold of achromatic target detection lies between 3.7° and 5°; the upper threshold between 15° and 10°. At the upper threshold, detection switches from chromatic-based to achromatic-based. Thus, in the context of target detection, the achromatic green contrast channel specialises in the detection of objects of reduced angular size, whilst the chromatic channels are specialised for objects of large angular size. We suggest that achromatic detectors with a centre-surround organisation are involved in the task of detecting achromatic targets.

Retinal image quality in the rodent eye

Abstract: Many rodents do not see well. For a target to be resolved by a rat or a mouse, it must subtend a visual angle of a degree or more. It is commonly assumed that this poor spatial resolving capacity is due to neural rather than optical limitations, but the quality of the retinal image has not been well characterized in these animals. We have modified a double-pass apparatus, initially designed for the human eye, so it could be used with rodents to measure the modulation transfer function (MTF) of the eye's optics. That is, the double-pass retinal image of a monochromatic (λ = 632.8 nm) point source was digitized with a CCD camera. From these double-pass measurements, the single-pass MTF was computed under a variety of conditions of focus and with different pupil sizes. Even with the eye in best focus, the image quality in both rats and mice is exceedingly poor. With a 1-mm pupil, for example, the MTF in the rat had an upper limit of about 2.5 cycles/deg, rather than the 28 cycles/deg one would obtain if the eye were a diffraction-limited system. These images are about 10 times worse than the comparable retinal images in the human eye. Using our measurements of the optics and the published behavioral and electrophysiological contrast sensitivity functions (CSFs) of rats, we have calculated the CSF that the rat would have if it had perfect rather than poor optics. We find, interestingly, that diffraction-limited optics would produce only slight improvement overall. That is, in spite of retinal images which are of very low quality, the upper limit of visual resolution in rodents is neurally determined. Rats and mice seem to have eyes in which the optics and retina/brain are well matched.

Method of and apparatus for controlling contrast of liquid crystal displays while receiving large dynamic range video

Abstract: An apparatus and method for controlling contrast for a liquid crystal display ('LCD'), especially active-matrix LCDs, while receiving large dynamic range video data to be displayed to the user by the LCD. Contrast settings of the LCD correspond to a single look-up table from a set of different and multiple look-up tables rather than using the contrast setting of the LCD to select different voltage values from a single look-up table. The values of the reference voltages of the LCD are varied so that all shades of gray are available with each contrast selection resulting in a high image quality and a high contrast.

Standard properties of ultrasound contrast agents

Abstract: A standardization procedure for in vitro acoustic characterization of ultrasound contrast agents is presented. One new acoustic parameter for particular importance is retained: This is STAR, scattering-to-attenuation ratio, for quantification of the effectiveness of the contrast agent. The STAR expresses the ability of the contrast agent to enhance the visualization of the tissue containing the contrast agent and, at the same time, represents the degree of its absorption. So, it is desirable to produce a contrast agent with high STAR, having good scattering properties to improve the image visualization, and low attenuation to image the underlying biological structures and to avoid shadowing. In this study, we present methods for calculations and measurements of the STAR and comparison between different contrast agents.

Near Real Time Confocal Microscopy of Cultured Amelanotic Cells: Sources of Signal, Contrast Agents and Limits of Contrast

Abstract: The use of high resolution, in vivo confocal imaging for noninvasive assessment of tissue pathology may offer a clinically important adjunct to standard histopathological techniques. To augment the present understanding of both the capabilities and limitations of in vivo confocal imaging, we investigated cellular sources of image contrast in amelanotic tissues, how contrast can be enhanced with external agents and how contrast is degraded by the scattering of overlying cells. A high-resolution reflected light confocal microscope was constructed and used to obtain images of various types of unstained amelanotic cells in suspension in real time before and after the addition of contrast agents. Reflectance images were compared to phase contrast images and electron micrographs to identify morphology visible with real time reflected light confocal microscopy. Mechanisms which decrease image contrast, including interference effects and scattering in overlying layers of cells, were considered. In amelanotic epithelial cells, fluctuations in the nuclear index of refraction provide signal which can be imaged even under several overlying cell layers. Acetic acid is an external contrast agent which can enhance this nuclear backscattering. Image contrast is degraded by the presence of multiple scattering in overlying cell layers. The degradation of image contrast by cell scattering depends on the scattering phase function; in vitro models which use polystyrene microspheres to approximate tissue underestimate the actual degradation caused by cell scattering. The loss in contrast can be explained using a finite difference time domain model of cellular scattering. We conclude that near real time reflected light confocal microscopy can be used to study cell morphology in vivo. Contrast degradation due to overlying tissue is a concern and cannot adequately be modeled using conventional tissue phantoms; however, acetic acid may be used to substantially increase intrinsic contrast, allowing imaging at significant depths despite distortion from overlying layers. © 1998 Society of Photo-Optical Instrumentation Engineers.

Limited translation invariance of human visual pattern recognition

Abstract: Visual object recognition is considered to be largely translation invariant. An earlier study (Foster & Kahn, 1985), however, has indicated that recognition of complex novel stimuli is partially specific to location in the visual field: It is significantly easier to determine the identity of two briefly displayed random patterns if both stimuli are presented at the same, rather than at different, locations. In a series ofsame/different discrimination tasks, we characterize the processes underlying this “displacement effect”: Horizontal and vertical translations are equally effective in reducing performance. Making the task more difficult by increasing pattern similarity leads to even higher positional specificity. The displacement effect disappears after rotation or contrast reversal of the patterns, indicating that positional specificity depends on relatively low levels of processing. Control experiments rule out explanations that are independent of visual pattern memory, such as spatial attention, eye movements, or retinal afterimages. Positional specificity of recognition is found only forsame trials. Our results demonstrate that position invariance, a widely acknowledged property of the human visual system, is limited to specific experimental conditions. Normalization models involving mental shifts of an early visual representation or of a window of attention cannot easily account for these findings.

Visual Correlates of Obstacle Avoidance in Adults with Low Vision

Abstract: This study examined how mobility performance in a heterogeneous sample of visually impaired adults relates to measures of visual sensory and perceptual function. We found that the best predictors of mobility performance under photopic and scotopic lighting conditions were models that incorporated visual field extent (VFE) and scanning ability. Together with measures of contrast sensitivity and spatial resolution, these models accounted for approximately 50% of the variance in mobility performance. We also found that VFE and scanning ability were the dominant predictor variables when the sample was broken down by subjects' type of vision loss into an acuity loss, a visual field restriction, and a combination loss group.

Responses of ganglion cells to contrast steps in the light-adapted retina of the tiger salamander

Abstract: The impulse discharge of single ganglion cells was recorded extracellularly in superfused eyecup preparations of the tiger salamander (Ambystoma tigrinum). Contrast flashes (500 ms) were applied at the center of the receptive field while the retina was light adapted to a background field of 20 cd/m2. The incidence of cell types in a sample of 387 cells was: ON cells (4%), OFF cells (28%), and ON/OFF cells (68%). Quantitative contrast/response measurements were obtained for 83 cells. On the basis of C50, the contrast necessary to evoke a half-maximal response, ON/OFF cells fell into 3 groups: (1) Positive Dominant (26%), (2) Balanced (23%), and (3) Negative Dominant (51%). Positive Dominant cells tended to be relatively contrast insensitive. On the other hand, many Negative Dominant cells showed remarkably low C50 values and very steep contrast/response curves. Contrast gain to negative contrast averaged 8.5 impulses/s/% contrast, some four times greater than that evoked by positive contrast. In most ON/OFF cells, the latency of the first spike evoked by a negative contrast step was much shorter (40-100 ms) than that evoked by a positive contrast step of equal contrast. OFF cells typically showed higher C50 values, larger dynamic ranges, and longer latencies than those of Negative Dominant ON/OFF cells. Thus, different pathways or mechanism apparently mediate the off responses of OFF and ON/OFF cells. In sum, the light-adapted retina of the tiger salamander is strongly biased in favor of negative contrast, as shown by the remarkably high contrast sensitivity and faster response of Negative Dominant cells, the remarkably low incidence of ON cells, and the insensitivity of Positive Dominant cells. Some possible underlying influences of bipolar and amacrine cells are discussed.

A perceptual distortion metric for digital color images

Abstract: This paper presents a comprehensive distortion metric for digital color images. It is based on a normalization model of the human visual system that incorporates color perception. The model is shown to accurately fit psychophysical contrast sensitivity data as well as intra- and inter-channel contrast masking data from several different psychophysical experiments. The output of the metric is compared with subjective data for natural images.

Normalized contrast sensitivity values.

Abstract: hroughout the history of refractive surgery, therapeutic procedures have been the focus of development. As the scope of treating refrac-tive disorders widens, there is increasing emphasis on diagnostic interventions that can help practitioners evaluate procedures with increased sophistication. It is not uncommon for patients to have visual complaints despite having 20/20 or better uncorrect-ed visual acuity. These occurrences highlight the need for sensitive tests of quality of vision. One study has shown that visual acuity did not significantly change following photorefractive keratecto-my (PRK), although contrast sensitivity was significantly decreased. 1 A mathematical model has shown the value of detecting subtle vision changes with contrast sensitivity. 2 Contrast sensitivity may be the method of choice because it is sensitive to changes in the refractive state, 3,4 but clinicians presently have difficulty using this test, which explains why it has remained predominantly in the research environment. Traditionally, charting the results of contrast sensitivity requires plotting curves on special graph paper (Fig 1). These curves are difficult to interpret in clinical practice, scientific presentation, and publication. Visual acuity, on the other hand, is reference based on the visual angle of resolution with familiar clinical notation, such as 20/20. Therefore, the clinician can understand the meaning of changes in visual acuity. What refractive surgery needs is a normalized notation for contrast sensitivity that is referenced to a normal population and can be incorporated into all contrast sensitivity devices. We introduce a novel method by which we generate a normalized notation of contrast sensitivity for two charts. METHODS AND RESULTS The contrast sensitivity of thirty-eight eyes of 19 healthy myopic individuals (ten male, nine female) was measured with two charts: 1) VectorVision CSV-1000E (VectorVision, Dayton, OH) without room lights and, 2) Stereo Optical F.A.C.T. (Stereo Optical, Chicago, IL) with luminance as per manufacturer guidelines (85 cd/m 2). Mean age was 34 years (range 26 to 44 yr). Mean and (standard deviation) for best spectacle-corrected logMAR visual acuity was-0.105 (SD .05) and spherical equivalent manifest refrac-tion was-3.91 diopters (D) (SD 2.33). The mean and standard deviation log contrast sensitivity values for the VectorVision CSV-1000E and Stereo Optical F.A.C.T. are shown in Table 1. These results are similar to those of a larger sample of over 100 eyes that is part of an ongoing FDA clinical trial. We determined the absolute log values and normalized ratios for the CSV-1000E chart and for the F.A.C.T. chart. The normalized …

Effect of Motion Contrast on Human Cortical Responses to Moving Stimuli

Abstract: Shulman, Gordon L., Jacob Schwarz, Francis M. Miezin, and Steven E. Petersen. Effect of motion contrast on human cortical responses to moving stimuli. J. Neurophysiol. 79: 2794–2803, 1998. The cort...

Comparison of methods to assess visual impairment from glare and light scattering with posterior capsule opacification.

Abstract: Purpose: To compare 2 glare tests to determine their relative usefulness in the assessment of posterior capsule opacification (PCO) and to evaluate the potential benefits of combined visual acuity, contrast sensitivity, and glare testing Setting: Teaching hospital ophthalmology department Methods: Sixteen patients had glare, visual acuity, and contrast sensitivity testing before and after neodymium:YAG (Nd:YAG) capsulotomy Results with the Brightness Acuity Tester (BAT, Mentor), which measures disability glare, and the Straylightmeter (Foundation for Eye Research, The Netherlands), which quantifies forward scatter by direct compensation techniques, were compared The correlation between glare, ETDRS visual acuity, and Pelli-Robson contrast sensitivity was determined Results: Pretreatment visual acuity was significantly correlated with contrast sensitivity (P 05), indicating that visual acuity is predictive of contrast sensitivity but a poor predictor of glare Glare was significantly improved (Straylightmeter, P < 0001; BAT, P < 05) following capsulotomy While the Straylightmeter consistently measured precapsulotomy forward scatter that improved with treatment, corresponding BAT disability glare was unmeasurable in 188% of patients with PCO, as their visual acuities improved rather than deteriorated with glare testing Conclusions: Glare testing provided more information than contrast sensitivity when combined with visual acuity in the evaluation of PCO Glare related to PCO is better assessed using the Straylightmeter because the BAT may yield aberrant disability glare results

Defining color borders in a raster image by identifying and breaking contrast ties

Abstract: A method and apparatus is disclosed for converting raster images into a vector format by identifying and converting the borders of image features into a mathematical format referred to as string sequences. To enable the string sequencing of color images, the present invention identifies and resolves contrast conflicts in the image features in order to avoid misperceiving the vectorized image when converted back into a raster format. A contrast conflict occurs when there is a “contrast tie” between overlapping features of the image. The feature that would normally be perceived as the dominant feature breaks the contrast tie so that when the vector image is reconstructed, the dominate feature appears in the foreground of the image while the recessive feature appears in the background. A contrast tie detector (CTD) performs a set of comparisons on the raw pixel data to detect the occurence of a contrast tie, and a contrast tie breaker (CTB) performs another set of comparisons on the raw pixel data to break the contrast tie. A contrast tie is broken by modifying a color identifier of a perimeter pixel relative to the color identifier of a target pixel, thereby enabling the correct string sequencing of color borders.