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At least 1,603 records · Page 89Linked to original sources
PubMed1998

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

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 sensitivity, visual field extent, glare disability, color confusion, motion sensitivity, spatio-temporal contrast sensitivity, scanning ability, and figure-ground discrimination were measured to determine their ability to predict mobility performance of visually impaired adults on indoor hallway and outdoor residential travel routes under photopic and mesopic lighting conditions. RESULTS: Time to complete routes and number of mobility incidents were significantly increased under mesopic conditions. Depending on the task, lighting conditions, and performance measure, predictive models consisting of 4 vision variables were able to account for 30 to 42% of the variance in overall performance. The two most important variables in these models were visual field extent and scanning ability, followed by color confusion, grating contrast sensitivity, or spatial resolution. CONCLUSIONS: Reducing illumination levels from photopic to mesopic has an adverse effect upon mobility in older visually impaired adults. The aspects of vision which best predict performance include measures of sensory and perceptual visual function. The results compare well with those obtained under controlled laboratory conditions.

Adaptation, Ocular↗
PubMed2005

Predicting components of closed road driving performance from vision tests.

PURPOSE: Mild cataracts can interfere with visually dependent everyday activities, although they only minimally affect static visual acuity. This study compared the effects of simulated cataracts with that of optical blur on driving performance and determined the extent to which acuity could account for variations in driving performance either alone or in combination with supplementary vision tests. METHODS: Closed road driving performance was measured in 24 young, normally sighted subjects under five binocular acuity levels, four produced by different levels of optical blur (6/4.5, 6/12, 6/30, 6/60) and one by frosted lenses simulating mild cataracts (6/12c). Driving measures included gap perception, total driving time, sign recognition, road hazard avoidance, maneuvering time, and errors. Subjects were also tested with the Pelli-Robson chart, SKILL card, and Berkeley Glare Test under comparable acuity levels. RESULTS: Total driving time, sign recognition, and hazard avoidance were linearly related to the acuity degradation produced by blur; performance in the 6/12c condition was similar to that in the 6/60 blur condition. Static acuity predicted 30% to 60% of the variance in these driving measures when the 6/12c condition was excluded from analysis; this proportion was reduced by a factor of two to three when the 6/12c condition was included. However, using any one of the three supplementary tests with visual acuity in a multiple regression analysis recaptured much of the lost variance. CONCLUSIONS: Static acuity can only predict variations in closed road driving performance measured under degraded conditions that include simulated mild cataracts when it is combined with supplementary vision tests.

Adult↗
PubMedDate not supplied

Vision screening of primary school children.

This week's report in Nursing Standard (p44) looks at the issues of vision screening for primary school children. In this article, the author describes how she carried out a study to explore whether there was an increase in the number of primary school children failing vision screening tests. During this exploratory study, the visual screening records of 3,447 children from eight Glasgow primary schools were examined. From 1989/90 and 1994/95 onwards, the author observed an increase in the number of children failing the visual acuity screening test. This article describes the study and the possible reasons for the findings.

Child↗
PubMed2004

[Quantitative assessment of quality of vision].

The importance of quality of vision (QOV) along with quality of life (QOL) in medicine has been recently widely recognized. We have conducted studies to quantitatively analyze factors related to QOV. Irregular astigmatism can be a significant obstacle for achieving satisfactory QOV. Videokeratography data were broken down using Fourier harmonic series analysis into spherical power, regular astigmatism (second harmonic component, n = 2), asymmetry (n = 1), and higher order irregularity (n > or = 3). The irregular astigmatism component calculated by the Fourier analysis significantly correlated with best spectacle-corrected visual acuity. Software was developed to display color-coded maps for the four Fourier indices. The normal range was defined for each Fourier index, and eyes with pathologic and postsurgical conditions were evaluated using the normal range. Progression of keratoconus over time was quantitatively described by Fourier analysis of the videokeratography data. Using the Fourier method, changes in corneal topography following suture removal after penetrating keratoplasty were evaluated. Fourier analysis of videokeratography data significantly facilitated determination of refraction and measurement of best spectacle-corrected visual acuity in eyes with corneal irregular astigmatism such as post-penetrating keratoplasty eyes. Higher-order wavefront aberrations of the cornea were calculated by expanding videokeratography elevation data into Zernike polynomials, and coma and spherical aberrations were computed. For ocular aberrations, the data obtained with the Hartmann-Shack sensor were decomposed into Zernike polynomials. Coma aberrations of the cornea significantly correlated with age, while corneal spherical aberrations showed no age-related changes. The time-course of changes in corneal higher-order aberrations was reported for photorefractive keratectomy and laser in situ keratomileusis (LASIK). For ocular aberrations, the degree of tilting of the suture-fixed intraocular lens significantly correlated with the amount of coma aberration of the eye. In normal eyes, the ocular coma increased with age mainly because of the increase in the corneal coma, and the ocular spherical aberration increased with age because of the increase in spherical aberration in the internal optics including the crystalline lens. The conventional LASIK significantly increased ocular higher-order aberrations, which compromised postoperative contrast sensitivity and low contrast visual acuity. Both corneal and ocular wavefront aberrations were analyzed in cataract, pseudophakic and aphakic eyes, and the equilibrium of spherical aberrations between the cornea and the eye in those conditions was investigated. In pseudophakic eyes, coma aberrations of the cornea, along with the corneal multifocality, significantly contributed to apparent accommodation. Computer simulation indicated that a focus shift of 0.5 diopters deteriorated the retinal image significantly more in eyes without higher-order aberrations than in eyes having a moderate amount of coma aberrations. Clinical results of aspherical intraocular lens were reported for wavefront analysis and contrast sensitivity measurements, and retinal images were analyzed by simulation. For the assessment of vision-related QOL, National Eye Institute Visual Functioning Questionnaire 25 (NEI-VFQ 25) was translated into Japanese. After the validation study, the influence of cataract surgery on QOL was investigated. The QOL score was severely impaired in patients with bilateral cataract, which was significantly and dramatically improved by surgery. Forward scattering, backward scattering, and wavefront aberration induced by the crystalline lens were quantified, and the impact of these factors on visual function was analyzed according to the type of cataract. The degree of QOL improvement by surgery was assessed in relation to the type of cataract and intensity of scattering and aberration. By comprehensively analyzing these factors, quantitative parameters could be developed in the near future to describe progression of cataract and determine the indication for cataract surgery.

Cataract Extraction↗
PubMed1993

Vision screening of individuals with severe or profound mental retardation.

A vision screening program was established at a regional center for individuals with severe or profound mental retardation. The visual acuity measure used was the acuity card procedure, a type of forced-choice preferential looking. Acuity values were evaluated in terms of test-retest reliability as well as inter- and intraobserver reliability. Acuity results compared favorably to those obtained in less compromised populations, and we conclude that the acuity card procedure is a useful screening tool for this population. Suggestions for its application in evaluating functional vision were also discussed.

Adolescent↗
PubMed2000

An automated machine vision system for the histological grading of cervical intraepithelial neoplasia (CIN).

The histological grading of cervical intraepithelial neoplasia (CIN) remains subjective, resulting in inter- and intra-observer variation and poor reproducibility in the grading of cervical lesions. This study has attempted to develop an objective grading system using automated machine vision. The architectural features of cervical squamous epithelium are quantitatively analysed using a combination of computerized digital image processing and Delaunay triangulation analysis; 230 images digitally captured from cases previously classified by a gynaecological pathologist included normal cervical squamous epithelium (n=30), koilocytosis (n=46), CIN 1 (n=52), CIN 2 (n=56), and CIN 3 (n=46). Intra- and inter-observer variation had kappa values of 0.502 and 0.415, respectively. A machine vision system was developed in KS400 macro programming language to segment and mark the centres of all nuclei within the epithelium. By object-oriented analysis of image components, the positional information of nuclei was used to construct a Delaunay triangulation mesh. Each mesh was analysed to compute triangle dimensions including the mean triangle area, the mean triangle edge length, and the number of triangles per unit area, giving an individual quantitative profile of measurements for each case. Discriminant analysis of the geometric data revealed the significant discriminatory variables from which a classification score was derived. The scoring system distinguished between normal and CIN 3 in 98.7% of cases and between koilocytosis and CIN 1 in 76.5% of cases, but only 62.3% of the CIN cases were classified into the correct group, with the CIN 2 group showing the highest rate of misclassification. Graphical plots of triangulation data demonstrated the continuum of morphological change from normal squamous epithelium to the highest grade of CIN, with overlapping of the groups originally defined by the pathologists. This study shows that automated location of nuclei in cervical biopsies using computerized image analysis is possible. Analysis of positional information enables quantitative evaluation of architectural features in CIN using Delaunay triangulation meshes, which is effective in the objective classification of CIN. This demonstrates the future potential of automated machine vision systems in diagnostic histopathology.

Female↗
PubMed1995

Comparison of direct vision and electronic two- and three-dimensional display systems on surgical task efficiency in endoscopic surgery.

Task efficiency and knot strength was evaluated under standardized conditions using direct vision and electronic imaging with two-dimensional (2-D) and three-dimensional (3-D) systems. Three operators with different endoscopic surgical experience tied a surgeon's knot with standard endoscopic instruments using the three different visual systems in random order. Each operator tied 20 knots with each visual system. Median task efficiency (defined as the time to complete the knot) was 35.0 (interquartile range (i.q.r.) 30.3-43.8) s for direct vision and 53.0 (i.q.r. 45.3-62.8) s and 53.5 (i.q.r. 45.0-64.8) s for 2-D and 3-D imaging respectively (P < 0.05). With respect to direct vision, this represented an overall degradation of task efficiency with the use of electronic imaging of 52 per cent, with no detectable difference between 2-D and 3-D imaging. The knot strength, representing the degree of tightening, was weaker with electronic imaging but the difference was not significant due largely to variation between the three operators.

Clinical Competence↗
PubMed1990

Striking absence of long-lasting effects of early color deprivation on monkey vision.

A monkey (Macaca fascicularis) spent its first three months under far red illumination that made color vision impossible. It developed normal spectral sensitivity. In the present study we examined two aspects of color vision that presumably reflect cortical connectivity. In the first part of this article we show that chromatic induction was also unaffected: a blue surrounding made a gray target appear to be yellow to the monkey. At five months of age, the deprived monkey did not readily use color to recognize objects, although it was able to do so if necessary. In the second part of this article we show that, as an adult, the monkey was quite willing to use color to categorize objects. We conclude that early color deprivation does not result in long lasting deficits in color vision.

Aging↗
PubMed2004

Evil by default: the origins of dark visions.

The growing body of literature on transformational change reflects an increasing interest among professionals in understanding epiphany and visionary change. However, we typically assume that such quantum changes are positive and pro-social ones. It is equally possible for an individual to lead a life that is organized around a motivating vision that is destructive to self, others, or both. The author examines the phenomenon of "dark visions," offering some hypotheses as to their origins. The article also offers strategies to minimize the number of individuals who choose dark visions, with all their unfortunate consequences.

Dangerous Behavior↗
PubMed1992

The spectral input systems of hymenopteran insects and their receptor-based colour vision.

Spectral sensitivity functions S(lambda) of single photoreceptor cells in 43 different hymenopteran species were measured intracellularly with the fast spectral scan method. The distribution of maximal sensitivity values (lambda max) shows 3 major peaks at 340 nm, 430 nm and 535 nm and a small peak at 600 nm. Predictions about the colour vision systems of the different hymenopteran species are derived from the spectral sensitivities by application of a receptor model of colour vision and a model of two colour opponent channels. Most of the species have a trichromatic colour vision system. Although the S(lambda) functions are quite similar, the predicted colour discriminability curves differ in their relative height of best discriminability in the UV-blue or blue-green area of the spectrum, indicating that relatively small differences in the S(lambda) functions may have considerable effects on colour discriminability. Four of the hymenopteran insects tested contain an additional R-receptor with maximal sensitivity around 600 nm. The R-receptor of the solitary bee Callonychium petuniae is based on a pigment (P596) with a long lambda max, whereas in the sawfly Tenthredo campestris the G-receptor appears to act as filter to a pigment (P570), shifting its lambda max value to a longer wavelength and narrowing its bandwidth. Evolutionary and life history constraints (e.g. phylogenetic relatedness, social or solitary life, general or specialized feeding behaviour) appear to have no effect on the S(lambda) functions. The only effect is found in UV receptors, for which lambda max values at longer wavelengths are found in bees flying predominantly within the forest.

Animals↗
PubMed1988

Form-vision deprivation amblyopia and strabismic amblyopia.

The treatment program for form-vision deprivation and strabismic amblyopia currently followed in our orthoptic clinic is presented. In unilateral congenital cataract, a disease that causes form-vision deprivation amblyopia, good vision up to 20/20 can be obtained through surgery performed before the patient reaches 8 weeks of age, employing new surgical techniques such as lentectomy and vitrectomy, combined with early aphakic eye correction and occlusion of the healthy eye. In strabismic amblyopia, prevention and/or early treatment are very important, particularly in cases of unilateral infantile esotropia. Our success rate with occlusion therapy was 84.6% using a patch and 83.3% employing atropine cycloplegia. Occlusion therapy is monitored with the preferential looking technique to prevent the development of occlusion amblyopia. The visual prognosis for amblyopia due to unilateral congenital cataract and infantile strabismic amblyopia has been improved compared with previous reports. The prognosis for binocular function remains poor.

Age Factors↗
PubMed2004

The utilization of visual feedback from peripheral and central vision in the control of direction.

Past research has demonstrated that both peripheral and central vision play an important role in the control of movement direction. However, it has been unclear whether the benefits of these sources of information are due to adjustments in the limb trajectory during movement execution (i.e., online) or modification in motor commands prior to movement initiation (i.e., offline). In the present paper, we analyzed the variability in limb trajectories in a directional aiming task to examine the relative contributions of peripheral and central vision in both the planning and execution of movements. The point of gaze was manipulated to vary where in the limb trajectory information was gained from central and peripheral vision. Analysis of the variability in directional error at various stages of the movement revealed that participants utilized information from early in the trajectory during movement execution when it appeared in both peripheral and central visual fields. Information from late in the trajectory was used offline to improve the programming of subsequent movements regardless of where this information was available in the visual field.

Adult↗
PubMed2000

Vision of the hand and environmental context in human prehension.

Previous findings on the role of visual contact with the hand in the control of reaching and grasping have been contradictory. Some studies have shown that such contact is largely irrelevant, while more recent ones have emphasised its importance. In contrast, information arising from the surrounding environment has received relatively little attention in the study of prehensile actions. In order to identify the roles of both sources of information, we made kinematic comparisons between three conditions. In the first, reaching was performed in a dimly lit room and compared with a second condition in which reaches in the dark, but with the thumb and first finger illuminated, were made to a luminous object. This contrast allows the effects of environmental context to be identified. A comparison between the second and a third condition, in which both vision of the hand and the environment was removed, but the object was still visually available, enabled the assessment of how and when vision of the hand plays a role. Removing environmental cues had effects both early and late in the reach, while vision of the hand was only crucial in the period after peak deceleration. In addition, removal of both sources of information resulted in larger grip apertures. Differences and similarities between our findings and those of other studies are discussed, as is the ongoing debate about the relative importance of visual feedback of the hand in the control and co-ordination of prehensile actions. We conclude with suggestions for further research based on the set-up used in the present study.

Adult↗
PubMed2000

Compound grating discrimination in extrafoveal and amblyopic vision.

Compound grating discrimination was measured in normal foveal and extrafoveal vision as well as in central vision of amblyopic subjects. Two types of discrimination were examined: 0 degrees versus 180 degrees and 90 degrees versus 270 degrees phase shift of the second harmonic relative to the fundamental. In common with several previous studies, we found that both 0/180 and 90/270 discriminations are possible in extrafoveal vision. However, we show that differences in foveal and extrafoveal sensitivity can be eliminated for both types of discrimination by scaling the stimulus size appropriately. The extent of spatial magnification necessary to equate foveal and extrafoveal performance differed markedly, with 90/270 discriminations requiring much more magnification. In the amblyopic subjects, the magnitude of the 90/270 deficit was greater than the 0/180 deficit in all six amblyopes tested. In common with previous investigations, we suggest that the visual system adopts a discrimination strategy, based upon differences in local features, between the patterns to be discriminated. One process registers positional relationships, while a second process registers local contrast differences. In this context, the reduced ability of the normal periphery and amblyopic fovea to perform mirror-symmetric discriminations is explained in terms of losses in positional acuity.

Amblyopia↗
PubMed1999

Dichromatic colour vision in an Australian marsupial, the tammar wallaby.

Despite earlier assertions that most mammals are colour blind, colour vision has in recent years been demonstrated in a variety of eutherian mammals from a wide range of different orders. This paper presents the first behavioural evidence from colour discrimination experiments, that an Australian marsupial, the tammar wallaby (Macropus eugenii), has dichromatic colour vision. In addition, the experiments show that the wallabies readily learn the relationship between the presented colours rather than the absolute hues. This provides a sensitive method to measure the location of the neutral-point, which is the wavelength of monochromatic light that is indistinguishable from white. This point is a diagnostic feature for dichromats. The spectral sensitivity of the wallabies' middle-wavelength-sensitive photoreceptor is known (peak: 539 nm) and the behavioural results imply that the sensitivity of the short-wavelength-sensitive receptor must be near 420 nm. These spectral sensitivities are similar to those found in eutherian mammals, supporting the view that the earliest mammals had dichromatic colour vision.

Animals↗
PubMed2001

Influence of three-dimensional vision on surgical telemanipulator performance.

BACKGROUND: Different viewing conditions (two- and three-dimensional National Television Standard Committee [2D-NTSC and 3D-NTSC] and two-dimensional high-definition television [2D-HDTV]) on telemanipulator performance were evaluated. METHODS: Six taskes were performed by 15 endoscopic surgeons using the daVinci telemanipulation system. Performance time and errors were measured. Encoder data from the system were used for kinematic analysis of motion. A self-evaluation questionnaire regarding performance under various viewing conditions was obtained. RESULTS: Resolution was better with 2D-HDTV. The estimate of relative distance was not influenced by the different visualization systems. Motor skill tasks were performed faster with binocular vision (3D-NTSC) than with monocular vision (2D-NTSC, 2D-HDTV). For both 2D settings, the deceleration phase of motion was prolonged (p < 0.05 vs 3D). Peak velocity was reduced with 2D-HDTV as compared with 3D-NTSC (p = 0.01). The surgeons tended to favor the 3D system despite their use of 2D systems in their own practice. CONCLUSIONS: Three-dimensional vision enhances telemanipulator performance as compared with a 2D system at the same or higher level of resolution. Because it allows faster and more precise movement, future surgical systems should focus on 3D visualization.

Depth Perception↗
PubMed1990

The independence of horizontal and vertical dimensions in handwriting with and without vision.

The purpose of this study was to investigate the relationship between horizontal and vertical components of handwriting production when subjects were instructed to vary the size of these components separately or together. The effect of vision on these instructed size transformations also was examined. Eight female adults participated in the experiment. The basic task was to write the words 'poppy' and 'wood' cursively five times, the first time in their normal size and then with four size transformations. These transformations--one-fourth, one-half, double, and four-times their normal size--were made under three different sets of instructions (width only, height only, both) and in two visual conditions (normal, blindfolded), for a total of six sets of five repetitions. The individual slopes (changes in actual values across the transformation values) for width and height under instructions to change both parameters were almost identical to the width and height slopes under instructions to change only the single parameter, supporting the notion of the independence of the horizontal and vertical components. Further, an analysis of these individual slopes indicated that the size transformations were significantly greater (p less than 0.05) (and closer to the instructed values) with vision than without vision.

Adult↗
PubMed1990

Integration of visual information and motor output in reaching and grasping: the contributions of peripheral and central vision.

This study examined the contributions made by peripheral and central vision to reaching and grasping. A specially designed contact lens system was used to restrict information to the peripheral retina. Modified goggles were used to restrict information to the central retina. A WATSMART motion analysis system was used to record and reconstruct three dimensional kinematic data. Analyses included an examination of peak kinematic values as well as a qualitative description of the trajectory profiles as related to transport and grasp components. With only peripheral vision, information related to size and shape of an object was inadequate, thus affecting the organization of both the transport and grasp components. With only central vision, information related to the location of an object was inadequate, affecting the organization of the transport but not the grasp component. Implications are discussed relevant to the current models of visuomotor control of reaching and grasping.

Adult↗