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At least 109 records · Page 6Linked to original sources
PubMedDate not supplied

Visual acuity in a community-dwelling Japanese population and factors associated with visual impairment.

PURPOSE: The aim of this study was to describe the distribution of visual acuity and investigate the predictors of visual impairment in a Japanese population. METHODS: Best-corrected visual acuity was measured in 2263 subjects aged 40-79 years randomly selected from a local community. Relations between visual impairment and possible risk factors were investigated. RESULTS: Among these subjects, 41 individuals (1.8%) were identified as visually impaired (best-corrected visual acuity in the better eye <0.5). Both sexes in the older age groups had a higher frequency of visual impairment (Mantel-Haenszel chi-square test: P<0.001). A multiple logistic regression indicated that an increase in age of 10 years [odds ratio (OR) 3.9; 95% confidence interval (CI) 2.3-6.7] and myopia (OR 2.9; 95%CI 1.4-6.0) were independent risk factors for visual impairment. Individuals with the highest level of education (college or higher) had a lower risk of visual impairment (OR 0.1; 95%CI 0-0.7) compared to individuals with the lowest level of education. CONCLUSIONS: As expected, visual impairment increased with advancing age, although the prevalence of visual impairment in our population was lower than in other surveys. Racial and regional differences and differences in study design may be responsible for discrepancies between surveys. It is noteworthy that myopia was a significant risk factor for visual impairment, although the reasons for this association are uncertain and need further investigation.

Adult↗
PubMed1984

Modifiability of responsiveness in a visual projection area of the chick brain: visual experience is only one of several factors involved.

The effects of visual experience on neuronal responsiveness in the hyperstriatum accessorium, a visual projection area, were investigated in 4 groups of domestic chicks, each comprising dark-reared (total = 44) and visually experienced (total = 34) birds. Visually experienced birds were placed singly in running wheels facing a flashing red light for 3 h; wheel revolutions were used as a measure of the chicks' locomotor activity. At approximately equal to 48 h after hatching each chick was anaesthetized and a microelectrode advanced in 250 micron steps through the left Wulst. After each step the responsiveness of units to diffuse retinal illumination (light flashes) was tested. Each recording site at which responses greater than or equal to 5 successive flashes could be evoked was classified as a response site. In some chicks at least one site responding briskly to greater than or equal to 15 successive flashes was found deep to the hyperstriatum accessorium. The zone of markedly increased responsiveness is referred to as the visually responsive lamina. The effect of visual experience on the response of units in the hyperstriatum accessorium varied between the groups of chicks. Visual experience did not significantly effect neuronal responsiveness in this region for chicks without a visually responsive lamina. For chicks with a lamina there was an effect of visual experience, but the effect again varied between groups. When data from inactive, visually experienced chicks were excluded, the group-to-group variation ceased to be significant. Thus visual experience alone was not adequate consistently to bring about long-term changes in the responsiveness of neurones in the hyperstriatum accessorium. Such experience was likely to increase neuronal responsiveness provided the chicks: were behaviourally active; and possessed a visually responsive lamina.

Animals↗
PubMed2004

Computerized kinetic perimetry detects tubular visual fields in patients with functional visual loss.

PURPOSE: To report a novel test that uses computerized kinetic perimetry to detect tubular visual fields in patients with functional visual loss. DESIGN: Observational case series. METHODS: Ten patients who demonstrated generalized visual field constriction on prior examinations underwent testing combining computerized kinetic perimetry with a reversed Galilean telescope, used for optical visual field expansion. RESULTS: Six patients with physiologic visual field constriction demonstrated expansion of their visual fields with the use of the reversed telescope. Four patients with functional visual loss responded to the reversed telescope by demonstrating tubular visual fields, with responses equal to or smaller than their demonstrated visual fields delineated without the telescope. CONCLUSIONS: This test uses a computerized kinetic examination to reduce the subjective nature of tangent screen testing for tubular visual fields and to provide a computerized recording of visual fields. This method is a novel and easy-to-use technique to demonstrate functional visual loss.

Computing Methodologies↗
PubMed2004

Complex visual hallucinations (Charles Bonnet syndrome) in visual field defects following cerebral surgery. Report of four cases.

The development of visual hallucinations after loss of vision is known as the Charles Bonnet syndrome. This phenomenon was first described in 1760 by Charles Bonnet and others during their observations of elderly patients with degeneration of the retina or cornea. To date a clear association between visual hallucinations and neurosurgical procedures has not been reported. Because of their clear demarcation, however, surgical lesions in the cerebrum offer a unique opportunity to determine the pathoanatomical aspects of visual hallucinations. During a 3-year period, 41 consecutive patients who acquired visual field defects after neurosurgery were examined for the occurrence of visual hallucination. Postoperatively, four of these patients experienced visual hallucinations. In two of them an upper quadrantanopia developed after the patients had undergone selective amygdalohippocampectomy. In the other two patients a complete hemianopia developed, in one case after resection of a parietal astrocytoma and in the other after resection of an occipital glioblastoma multiforme. The visual hallucinations were transient and gradually disappeared between 4 days and 6 months postoperatively. The patients were aware of the fact that their hallucinations were fictitious and displayed no psychosis. Electroencephalographic recordings were obtained in only two patients and epileptic discharges were found. Deafferentiation of cortical association areas may lead to the spontaneous generation of complex visual phenomena. In the present series this phenomenon occurred in approximately 10% of patients with postoperative visual field defects. In all four cases the central optic radiation was damaged between the lateral geniculate nucleus and the primary visual cortex. The complex nature of the visual hallucination indicates that they were generated in visual association areas.

Adult↗
PubMedDate not supplied

Relationship between performance on tests of basic visual functions and visual-perceptual processing in persons after brain injury.

OBJECTIVE: In this correlational study of adults receiving occupational therapy who sustained a cerebrovascular accident (CVA), the relationship between basic visual functions (including acuity, visual field deficits, oculomotor skills, and visual attention or scanning) and higher level visual-perceptual processing skills (e.g., visual closure and figure-ground discrimination) was investigated. METHOD: Thirty adults who sustained CVA and 20 adults without a history of CVA were given a basic visual function screening and the Motor-Free Visual Perception Test (MVPT). Scores on the vision screening and the MVPT were correlated statistically. RESULTS: A Pearson product-moment correlation analysis produced a correlation of r = .75 between vision screening scores and scores from the MVPT. CONCLUSION: These results suggest that a positive relation exists between basic visual functions and visual-perceptual processing skills. Further, the results suggest that evaluation of visual-perceptual processing skills must begin with assessment of basic visual functions so that the influence of these basic visual functions on performance in more complex tests can be taken into consideration.

Accommodation, Ocular↗
PubMed2006

Studies of human visual pathophysiology with visual evoked potentials.

Visual evoked potentials (VEPs) offer reproducible and quantitative data on the function of the visual pathways and the visual cortex. Pattern reversal VEPs to full-field stimulation are best suited to evaluate anterior visual pathways while hemi-field stimulation is most effective in the assessment of post-chiasmal function. However, visual information is processed simultaneously via multiple parallel channels and each channel constitutes a set of sequential processes. We outline the major parallel pathways of the visual system from the retina to the primary visual cortex and higher visual areas via lateral geniculate nucleus that receive visual input. There is no best method of stimulus selection, rather visual stimuli and VEPs' recording should be tailored to answer specific clinical and/or research questions. Newly developed techniques that can assess the functions of extrastriate as well as striate cortices are discussed. Finally, an algorithm of sequential steps to evaluate the various levels of visual processing is proposed and its clinical use revisited.

Brain Diseases↗
PubMed2005

Effects of increasing visual load on aurally and visually guided target acquisition in a virtual environment.

The aim of the present study is to investigate interactions between vision and audition during a target acquisition task performed in a virtual environment. We measured the time taken to locate a visual target (acquisition time) signalled by auditory and/or visual cues in conditions of variable visual load. Visual load was increased by introducing a secondary visual task. The auditory cue was constructed using virtual three-dimensional (3D) sound techniques. The visual cue was constructed in the form of a 3D updating arrow. The results suggested that both auditory and visual cues reduced acquisition time as compared to an uncued condition. Whereas the visual cue elicited faster acquisition time than the auditory cue, the combination of the two cues produced the fastest acquisition time. The introduction of secondary visual task differentially affected acquisition time depending on cue modality. In conditions of high visual load, acquiring a target signalled by the auditory cue led to slower and more error-prone performance than acquiring a target signalled by either the visual cue alone or by both the visual and auditory cues.

Adolescent↗
PubMed2005

Acetylcholine release is elicited in the visual cortex, but not in the prefrontal cortex, by patterned visual stimulation: a dual in vivo microdialysis study with functional correlates in the rat brain.

By its projections to the primary visual and the prefrontal cortices, the basal forebrain cholinergic system is involved in cognitive processing of sensory stimuli. It has been suggested that visual stimulus-induced cholinergic activation of the visual cortex may exert a permissive role on thalamocortical inputs. However, it is not known if visual stimulation elicits cholinergic activation of high-order brain areas in the absence of attentional need. In the present study, we measured the effects of patterned visual stimulation (horizontal grating) on the release of acetylcholine with dual-probe in vivo microdialysis in the visual and the prefrontal cortices of anesthetized rats. We also used retrograde tracing to determine the anatomical relationships of cholinergic neurons with neurons of the visual system and the prefrontal cortex. Finally, we evaluated a functional correlate of this stimulation, namely c-fos immunolabeling. Patterned visual stimulation elicited significant increases in acetylcholine release in the visual cortex, accompanied by an increased number of c-fos immunoreactive neurons in this brain area. In contrast, in the prefrontal cortex, neither the level of acetylcholine release nor the number of c-fos immunoreactive neurons was significantly changed because of the stimulation. Cholinergic basal forebrain neurons projecting to the visual or the prefrontal cortices were both localized within the horizontal limb of the diagonal band of Broca but were not immunoreactive for c-fos during visual stimulation. No parts of the visual system were found to directly project to these basal forebrain neurons. These results suggest the differential involvement of cholinergic projections in the integration of sensory stimuli, depending on the level of activity of the targeted cortical area.

Acetylcholine↗
PubMedDate not supplied

Spatial representations and multiple-visual-systems hypotheses: evidence from a developmental deficit in visual location and orientation processing.

AH, a young, well-educated woman, has a developmental deficit in processing visual location and orientation information. Her deficit manifests itself in a wide range of visual tasks, including visually-guided reaching, copying pictures and words, and responding verbally to the location or orientation of visual stimuli; however, her performance in non-visual localization tasks is intact. AH's visual location and orientation errors are systematic left-right or up-down reflections (e.g., reaching to the far right for an object on the far left). More specifically, the errors involve reflection across the point where AH's attention is focused, regardless of where her eyes are fixated. These results imply that at some level(s) of the visual system, locations and orientations of visual stimuli are represented in a spatial coordinate system with an origin defined by the focus of attention. In these attention-centered representations location is specified in terms of distance and direction of displacement from the attentional focus along horizontal and vertical reference axes. AH's errors, I argue, result from misrepresentation of displacement direction (e.g., left rather than right, down rather than up) along a reference axis. Several visual variables dramatically affected AH's performance in visual location and orientation tasks: She was much more accurate for stimuli that were brief, moving, flickering, low in contrast, or high in eccentricity, than for those that were long in duration, stationary, continuous, high in contrast, and low in eccentricity. These results suggest that location and orientation are computed in each of two visual subsystems, which I call transient and sustained, and that AH's deficit affects only the sustained subsystem. I argue that AH's performance poses challenges to multiple-visual-subsystems hypotheses proposed by Ungerleider and Mishkin (1982) and by Milner and Goodale (1995).

Adult↗
PubMed2004

Screening for myopia and refractive errors using LogMAR visual acuity by optometrists and a simplified visual acuity chart by nurses.

PURPOSE: To compare the sensitivity and specificity of a widespread method of screening for refractive errors in Singapore schoolchildren using a simplified acuity screening chart with a more rigorous method using the Early Treatment Diabetic Retinopathy Study (ETDRS) chart. A secondary aim is to estimate the best cutoff values for the detection of refractive errors using these two methods. METHODS: This is a population-based study, involving 1779 schoolchildren from three schools in Singapore. Logarithm of the minimum angle of resolution (logMAR) visual acuity was recorded using a modified Bailey-Lovie chart by trained optometrists, and visual acuity measurement was also undertaken using a simplified 7-line visual acuity screening chart by school health nurses. The main outcome measures were the receiver-operating characteristics (ROC's) of logMAR and the simplified screening visual acuity to detect myopia or any refractive errors. The difference between measurements, simplified screening visual acuity--logMAR visual acuity, was calculated. RESULTS: The optimal threshold using the simplified screening visual acuity chart for the detection of myopia or any refractive error was 6/12 or worse. Using logMAR visual acuity, the most efficient threshold for the detection of myopia was 0.26, but this was 0.18 for the detection of any refractive error. The area under the ROC curves was significantly greater in the case of the logMAR visual acuity measurement compared with the simplified screening visual acuity measurement for the detection of myopia or any refractive errors. The 95% limits of agreement for the two methods (simplified screening--logMAR acuity) was -0.219 to +0.339. CONCLUSIONS: Bearing in mind that the visual acuity measurements were performed by two different groups of professionals, visual acuity screening using the ETDRS method appears to be more accurate than the simplified charts for the detection of myopia or any refractive errors in children.

Child↗
PubMedDate not supplied

Visual signatures in video visualization.

Video visualization is a computation process that extracts meaningful information from original video data sets and conveys the extracted information to users in appropriate visual representations. This paper presents a broad treatment of the subject, following a typical research pipeline involving concept formulation, system development, a path-finding user study, and a field trial with real application data. In particular, we have conducted a fundamental study on the visualization of motion events in videos. We have, for the first time, deployed flow visualization techniques in video visualization. We have compared the effectiveness of different abstract visual representations of videos. We have conducted a user study to examine whether users are able to learn to recognize visual signatures of motions, and to assist in the evaluation of different visualization techniques. We have applied our understanding and the developed techniques to a set of application video clips. Our study has demonstrated that video visualization is both technically feasible and cost-effective. It has provided the first set of evidence confirming that ordinary users can be accustomed to the visual features depicted in video visualizations, and can learn to recognize visual signatures of a variety of motion events.

Algorithms↗
PubMedDate not supplied

Comparison of subjective visual acuity with visual acuity predicted from C-scan topography.

PURPOSE: To compare the capability of objective measures of visual acuity (potential visual acuity from C-scan) to predict subjective visual acuity (best spectacle-corrected visual acuity [BSCVA]). METHODS: Patients with BSCVA > or = 20/20 were enrolled in four groups (Group 1: normal [33 eyes]; Group 2: < -7.00 D myopia [43 eyes]; Group 3: > or = -7.00 D myopia [28 eyes]; Group 4: At least 1 month after LASIK [93 eyes]). Videokeratography was performed with the ray tracing Technomed C-scan. The potential visual acuity from C-scan was obtained with pupils undilated and intact precorneal tear films. All visual acuity was recorded in logMAR, and the significance of differences between acuities was assessed with a one-way ANOVA test. RESULTS: The potential visual acuity from C-scan ray tracing of normal and myopic eyes in response to both photopic and mesopic stimuli did not differ. In a given eye, the potential visual acuity from C-scan ray tracing was better than BSCVA, and the difference was statistically significant. Although the potential visual acuity from C-scan of postoperative LASIK eyes in response to photopic stimuli was the same, it decreased under mesopic conditions. CONCLUSIONS: Potential visual acuity from C-scan overestimates subjective visual acuity due to the inadequate assumptions in ray tracing or individual retinal resolution ability. In addition, the potential visual acuity from C-scan ray tracing varies with pupil diameter in different illumination.

Adolescent↗
PubMed1997

Visual field constriction as a cause of blindness or visual impairment.

Reported are the results of a study of onchocerciasis in communities mesoendemic for savanna onchocerciasis in Kaduna State, northern Nigeria. The study involved 6831 individuals aged > or = 5 years who underwent an extensive screening examination for visual function including Friedmann field analysis. A total of 185 (2.7%) were bilaterally blind by acuity and an additional 28 (0.4%) were blind by visual field constriction. Also 118 (1.7%) individuals were visually impaired by acuity criteria. No criteria for visual impairment by field constriction have been established, and we therefore investigated three potential criteria. As a result, a further 60 (0.9%) individuals were identified with significant visual impairment due to field loss by the various definitions. Small islands of remaining peripheral field occurred in 50 individuals, while 40 individuals had marked reduction of binocular visual field below the horizontal meridian. Concentric visual field constriction to < 20 degrees was found in seven individuals. The WHO definition of blindness currently includes visual field damage criteria for blindness but not for visual impairment. Visual field loss is recognized as a major disability. We hope that these findings stimulate international discussion leading to the development of satisfactory definitions for visual impairment by visual field constriction.

Adolescent↗
PubMed2000

The advanced glaucoma intervention study, 6: effect of cataract on visual field and visual acuity. The AGIS Investigators.

OBJECTIVE: To investigate the effect of cataract on visual function and the role of cataract in explaining a race-treatment interaction in outcomes of glaucoma surgery. METHODS: The Advanced Glaucoma Intervention Study (AGIS) enrolled 332 black patients (451 eyes) and 249 white patients (325 eyes) with advanced glaucoma. Eyes were randomly assigned to an argon laser trabeculoplasty (ALT)-trabeculectomy-trabeculectomy sequence or a trabeculectomy-ALT-trabeculectomy sequence. From the AGIS experience with cataract surgery during follow-up, we estimated the expected change in visual function scores from before cataract surgery to after cataract surgery. Then, for eyes with cataract not removed, we used these estimates of expected change to adjust visual function scores for the presumed effects of cataract. In turn, we used the adjusted scores to obtain cataract-adjusted main outcome measures. MAIN OUTCOME MEASURES: Average percent of eyes with decrease of visual field (APDVF) and average percent of eyes with decrease of visual acuity (APDVA). RESULTS: Within the 2 months before cataract surgery, visual acuity was better in eyes of white patients than of black patients by an average of approximately 2 lines on the visual acuity test chart. Cataract surgery improved visual acuity and visual field defect scores, with the amounts of improvement greater when preoperative visual acuity was lower. Adjustments for cataract brought about the following relative reductions: for APDVF, a relative reduction of 5% to 11% in black patients and 9% to 11% in white patients; for APDVA, a relative reduction of 45% to 49% in black patients and 31% to 38% in white patients; and for the APDVF and APDVA race-treatment interactions, relative reductions of 25% and 45%, respectively. CONCLUSIONS: On average, visual function scores improved after cataract surgery. The findings of reduced race-treatment interactions after adjustment for cataract do not alter our earlier conclusion that the AGIS 7-year results support use of the ALT-trabeculectomy-trabeculectomy sequence for black patients and of the trabeculectomy-ALT-trabeculectomy sequence for white patients without life-threatening health problems. The choice of treatment should take into account individual patient characteristics and needs.

Adult↗