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At least 469 records · Page 26Linked to original sources
PubMed2006

Visual impairment and the useful field of vision.

The aim of this study was to measure the useful field of vision (UFoV) in people with visual impairment and to compare results with clinical measures of vision. UFoV, visual acuity, contrast sensitivity and visual fields were measured in 36 participants with low vision and 22 age-matched controls in two age groups. For both the low vision and control groups the presence of distractors (cluttered field) increased the error rates on our UFoV measure but there was no significant effect of the presence of a central task (divided attention). Participants with low vision made more errors on UFoV than did controls, but this difference disappeared once their visual field defects were accounted for. By multiple regression analysis, age, visual fields and contrast sensitivity were shown to predict the different UFoV scores. As for observers with normal vision, standard clinical visual field tests may not fully describe the difficulties that may be encountered by people with visual impairment undertaking tasks in the cluttered environments and multiple demands of everyday life.

Adult↗
PubMed1998

[A simplified screening test for the identification of individuals with diminished vision in developing countries].

Simple but effective tests have been produced for screening subjects with low vision in developing countries. These tests of distance and near vision, based on the E test, were evaluated and validated in trials with people aged 4-90 years, and have been field tested in the health, education and rehabilitation services in 32 developing countries. Their sensitivity and specificity as screening tools for low vision have been calculated: sensitivity of 85% and specificity of 96% for the distance vision test, and sensitivity of 100% and specificity of 84% for the near vision test. The content and format of the tests have been demonstrated to be appropriate for developing countries, and their effectiveness for screening for low vision has been confirmed.

Adolescent↗
PubMed1990

[Neuro-otological studies on the correlation between vision and oculomotor function tests].

The vision of 35 subjects with normal oculomotor function was artificially reduced with the use of convex and concave lenses and neutral density filters. The effects of blurred vision on the oculomotor function test were subsequently studied. In using neutral density filters, abnormal findings tended to be confirmed in the eye tracking test (ETT) and optokinetic nystagmus test (OKNT) for vision of 0.5 or less. However, the ratio of abnormal findings to the ETT markedly decreased as the intensity of the target luminance increased. Blurred vision due to refractive abnormality using lenses, had hardly any effect was detected on either test even in the cases of severe blurred vision. In conclusion, the effects on the oculomotor function test varied according to causes of blurred vision.

Electronystagmography↗
PubMed2005

Comparative use of color vision for frugivory by sympatric species of platyrrhines.

Ateles spp. and Alouatta spp. are often sympatric, and although they are mainly frugivorous and folivorous, respectively, they consume some of the same fruit species. However, they differ in terms of color vision, which is thought to be important for fruit detection. Alouatta spp. have routine trichromatic color vision, while Ateles spp. presents the classic polymorphism of platyrrhines: heterozygous females have trichromatic color vision, and males and homozygous females have dichromatic vision. Given these perceptual differences, one might expect Alouatta spp. to consume more reddish fruits than Ateles spp., since trichromats have an advantage for detecting fruits of that hue. Furthermore, since Ateles spp. have up to six different color vision phenotypes, as do most other platyrrhines, they might be expected to include fruits with a wider variety of hues in their diet than Alouatta spp. To test these hypotheses we studied the fruit foraging behavior of sympatric Alouatta palliata and Ateles geoffroyi in Costa Rica, and modeled the detectability of fruit via the various color vision phenotypes in these primates. We found little similarity in fruit diet between these two species (Morisita = 0.086). Furthermore, despite its polymorphism, A. geoffroyi consumed more reddish fruits than A. palliata, which consumed more greenish fruits. Our modeling results suggest that most fruit species included in the diet of A. geoffroyi can be discriminated by most color vision phenotypes present in the population. These findings show that the effect of polymorphism in platyrrhines on fruit detection may not be a disadvantage for frugivory. We suggest that routine trichromacy may be advantageous for other foraging tasks, such as feeding on young leaves.

Alouatta↗
PubMed1996

[Comparative study of various 2-D and 3-D vision systems in minimally invasive surgery].

The aim of this comparative study was to gain subjective and objective data to determine for which operative tasks it is useful to work with 3-D rather than 2-D vision systems and to show the advantages and disadvantages of 3-D systems. A series of five standardized tasks like sewing and tying knots was set up to measure performance times objectively and to count errors. Compared with 2-D vision, the performance time was 32% shorter and 43% fewer errors were made under 3-D vision (P < 0.001). In our endoscopic training centre, surgeons involved in basic and advanced laparoscopic courses trained using both 2-D and 3-D vision systems. They subsequently completed analogue scale questionnaires to record a subjective impression of comparative ease of operation tasks under 2-D and 3-D vision, and to identify perceived deficiencies in the 3-D system. In both courses, all operative tasks were judged significantly easier under 3-D vision (P < 0.001). It was concluded that users with a normal capacity for spatial perception can work faster and safer under 3-D vision, especially for more complicated surgical manoeuvres.

Animals↗
PubMed1998

Comparative study of two-dimensional and three-dimensional vision systems for minimally invasive surgery.

BACKGROUND: The aim of this comparative study was to gain subjective and objective data to determine for which operative tasks three-dimensional (3-D) vision systems are superior to two-dimensional (2-D) systems and to demonstrate any advantages or disadvantages of 3-D systems. METHODS: A model with five standardized tasks including sewing and knotting was developed to objectively measure performance times and to count technical faults. In our training center for minimally invasive surgery, surgeons involved in basic and advanced laparoscopic courses trained using both 2-D and 3-D vision systems. They subsequently completed analog scale questionnaires to record a subjective impression of comparative ease of operation tasks under 2-D and 3-D vision and to identify perceived deficiencies in the 3-D system. RESULTS: Compared to 2-D vision, the objective performance time was significantly shorter and significantly less mistakes were made using 3-D vision. All operative tasks were subjectively judged significantly easier under 3-D vision. CONCLUSIONS: Users with a normal capability for spatial perception can perform standard tasks more quickly and safely using 3-D vision, and a greater benefit is apparent for more complicated surgical maneuvers.

Depth Perception↗
PubMed2001

Double Vision.

When evaluating a patient with a complaint of double vision, it is important to distinguish monocular versus binocular diplopia, which are differentiated by asking the patient to cover each eye separately. In the setting of binocular double vision, one of the two images disappears when either eye is covered, because diplopia is the result of ocular misalignment. On the other hand, monocular double vision resolves when the affected eye is covered, but remains when the opposite eye is occluded. Causes of monocular diplopia include cataract, refractive error, and retinal disease, which can be managed accordingly by an ophthalmologist. However, an unusual form of monocular double vision can occur in the setting of cortical dysfunction. Cerebral polyopia describes the perception of multiple images and arises from an occipital disturbance. It can occur with migraine headaches and can be accompanied by a homonymous hemianopia. Palinopsia refers to the persistence of an image that is no longer in view (visual perseveration or stroboscopic effect) and results from an occipital lesion as well. The exact mechanism of polyopia and palinopsia are uncertain and both conditions are extremely rare. The majority of this discussion will focus on binocular double vision and its management. The main treatment objective of binocular diplopia is to restore the largest area of single binocular vision. Ideally, patients would be able to achieve single vision in all fields of gaze, but this is not always possible. The majority of patients are treated with either prism lenses or eye muscle surgery.

Journal Article↗
PubMed2004

Transient Vision Loss.

Transient vision loss often presents a diagnostic dilemma and may occur in many different settings. Episodic vision loss is a common complaint and the physician must distinguish whether the transient vision loss is benign or representative of a more serious underlying condition. Common causes of transient vision loss include ischemia and primary ocular pathology. Ischemic causes of vision loss include retinal vascular disease, intermittent optic nerve vascular compromise, or cerebrovascular disease. Many pathologic ocular processes may lead to transient vision loss, including tear film abnormalities and corneal diseases. The authors discuss the clinical presentation and management of transient vision loss, with special attention on characteristics that differentiate vascular disease from primary ocular pathology.

Journal Article↗
PubMed2006

Minimal depression and vision function in age-related macular degeneration.

OBJECTIVE: To evaluate the impact of minimal depression on subjective and objective vision function measures in age-related macular degeneration (AMD). DESIGN: Prospective cross-sectional study. PARTICIPANTS: Two hundred six outpatients with newly diagnosed neovascular AMD in one eye and preexisting AMD in the fellow eye. METHODS: Structured clinical evaluations of visual acuity (VA), contrast sensitivity, vision function, and depression. MAIN OUTCOME MEASURES: The 17-item National Eye Institute Visual Function Questionnaire (NEI VFQ 17), Melbourne Low-Vision Index (MLVI), Chronic Disease Score, and Hamilton Depression Rating Scale. RESULTS: Minimally depressed subjects had significantly worse vision function on both the NEI VFQ 17 and performance-based tasks of the MLVI than nondepressed subjects, independent of severity of VA, contrast sensitivity, and medical status. CONCLUSIONS: Minimally depressed patients with AMD, who would not be considered depressed according to current diagnostic standards, suffer decrements in vision function that cannot be accounted for by the severity of their eye disease or general medical problems. These data emphasize the need to assess depressive symptoms in research studies that use vision function outcome measures and in clinical practice to identify excess vision-related disability in patients with AMD.

Aged↗
PubMed1999

Can injury prevention efforts go too far? Reflections on some possible implications of Vision Zero for road accident fatalities.

The Swedish National Road Administration has launched a long term vision of a road transport system in which nobody is killed or sustains an injury resulting in permanent impairment (Vision Zero). This paper examines some possible implications of Vision Zero for traffic fatalities. The main points of the paper can be summarised as follows: An objective of eliminating traffic deaths can be interpreted as an application of a general principle of minimising mortality. Minimising overall mortality implies that a survival lottery must be introduced, at any rate as long as there is a shortage of organs for transplants. A survival lottery is a scheme in which people are drawn at random to sacrifice their life for the benefit of others. An objective of eliminating a certain cause of death, like traffic accidents, may be so expensive to realise that there is so much less resources available to control other causes of death that general mortality increases. Several analyses of the relationship between income per capita and general mortality based on Norwegian data document a negative relationship between income and mortality. The loss of income that induces an additional statistical death, due to economic inefficiency, is estimated to between 25 and 317 million NOK (3.8-47.5 million US dollars). These estimates are in line with those of most previous studies. No study of the relationship between income and mortality fully satisfies commonly used criteria of causality. However, the balance of evidence suggests that the relationship between income and mortality is a causal one. A hypothetical programme designed to implement Vision Zero for traffic fatalities was developed and its effects on the number of fatalities estimated. Implementing the whole programme could reduce the number of traffic deaths in Norway from about 300 per year to about 90 per year. Applying the lowest estimate of the income loss that induces an additional death (25 million NOK), it was estimated that implementing the entire hypothetical Vision Zero programme would increase general mortality by about 1355. This would lead to a net increase of about 1145 deaths per year (1355 minus 210 prevented traffic deaths). The analyses presented in this paper show that the possibility cannot be ruled out that a massive effort to eliminate traffic deaths would be counterproductive in terms of overall mortality. This possibility must be regarded as a moral dilemma by advocates of Vision Zero, who have invoked the ethical principle that 'one must always do everything in one's power to prevent death or serious injury' to justify the vision.

Accidents, Traffic↗
PubMed1999

Manipulation with no or partial vision.

The present research investigated the role of vision in closed- and open-loop processing during manipulation. In Experiment 1, participants performed common manipulatory tasks with 100% accuracy in less than 1 s without vision. In Experiment 2, the effects of extensive practice of a peg-in-hole task were examined within 4 functionally significant stages of manipulation. Performance was consistently faster with than without vision in the prereach, grasp, and transport + insert stages; reverse effects were observed during the reach stage. In Experiment 3, the effects of practice with partial vision were examined: Participants initially learned the peg-in-hole task with full vision and then transferred to learning the same task with vision available only during 1 functional stage. Overall, performance was fastest when vision was limited to the prereach and reach stages.

Adolescent↗
PubMed1996

Trichromatic colour vision in New World monkeys.

Trichromatic colour vision depends on the presence of three types of cone photopigment. Trichromacy is the norm for all Old World monkeys, apes and humans, but in several genera of New World monkeys, colour vision is strikingly polymorphic. The difference in colour vision between these New and Old World primates results form differing arrangements of the pigment genes on the X chromosome. In Old World primates the three photopigments required for routine trichromatic colour vision are encoded by two or more X-chromosome pigment genes and an autosomal pigment gene. New World monkeys typically have only one X-chromosome pigment gene; multiple alleles allow different types of dichromatic colour vision and, in female heterozygous at this locus, variant forms of trichromatic colour vision. Here we report that multiple X-chromosome pigment genes and trichromatic colour vision are the norm for one genus of platyrrhine monkey, the howler monkey, Alouatta.

Alouatta↗
PubMed2000

3-D vision improves performance in a pelvic trainer.

BACKGROUND AND STUDY AIMS: Experienced endoscopic surgeons have adapted to the absence of depth perception while using two-dimensional (2-D) visualization. However, three-dimensional (3-D) vision may prove useful at least at the beginning of the learning curve in celioscopic training. METHODS: In a pelvitrainer with a fixed camera, two skill tests were designed to assess the performance of three groups of operators: "non-surgeons", "non-celioscopist surgeons", and "trained celioscopists". In the first test, the candidate had to touch with a needle a sequence of dots distributed on a 7.1-cm2 area. In the second test, a 6-0 C-1 needle had to be passed consecutively through two 1-mm holes made in a thin vertical plastic wall. Each test was performed ten times, using either 2-D vision (five times) or 3-D vision (five times) interspersed in a random manner. RESULTS: In both tests and within each group, performance was related to the experience of the operator, with the trained celioscopists' group obtaining the best results and the non-surgeons the worst. In every situation, including the trained celioscopists' group, 3-D vision significantly improved performances. No significant difference was observed between the results of the non-celioscopist surgeons' group using 3-D vision and those of the trained celioscopists' group using 2-D vision. CONCLUSIONS: 3-D vision improves the performance and accuracy of endoscopic surgeons. It provides a visual perception "close to reality", and helps celioscopic beginners to accelerate their training.

Adult↗
PubMed1990

Molecular genetics of X chromosome-linked color vision among populations of African and Japanese ancestry: high frequency of a shortened red pigment gene among Afro-Americans.

Red-green color vision in humans is mediated by the X chromosome-linked highly homologous red and green pigment genes. Color vision defects are caused by deletions and fusions involving these genes. However, we found the frequency of molecular abnormalities among Caucasians to be twice as high as that of phenotypic color vision defects. Among Japanese the frequency of phenotypic and molecular color vision defects was similar (approximately 5%). Among Afro-Americans, molecular defects (largely green-red fusion genes) were at least five times more frequent (21%) than phenotypic color vision defects (approximately 4%). In addition, 35% of Afro-Americans, 2% of Japanese, and less than 1% of Caucasians had a shortened red pigment gene not associated with phenotypic color vision defects. This gene lacked 1.9 kilobases in its first intron and had the identical size as the green pigment gene from which it presumably originated by gene conversion in an ancestral African population. This gene and the closely linked glucose-6-phosphate dehydrogenase A+ variant were in linkage equilibrium. A model for the evolutionary origin of the color vision pigment genes in higher primates is portrayed.

Black People↗
PubMed1982

Visions and psychopathology in the Middle Ages.

Descriptions of visionary experience from written medieval sources are examined from a cross-cultural perspective. The mental states of the persons having the visions range from terminal illnesses, states of starvation, stress-related syndromes, dreams and hypnagogic states, and seemingly unremarkable mental states. Although a few of the visions elicited some skepticism on the part of contemporaries, most reports of visions were accepted at face value as bona fide visions, with no discernible differentiation between starvation visions, dreams, deliria of illnesses, and possible mental illness. Only four of the visions appeared causally related, by today's standards, to mentally illnesses. These persons were not recognized as mentally ill by their contemporaries. Since there was a recognition of mental illness in the Middle Ages, it would appear that such recognition was based on symptoms other than visions or hallucinations. It is also possible that hallucinations, as culturally supported phenomena, were not as available as forms of expression of psychoses in the Middle Ages as they are today. Such a possibility has interesting implications regarding the role of a culture in shaping the forms by which mental illnesses are expressed, recognized, and labeled.

Alcoholism↗
PubMed2005

Non-random association of opsin alleles in wild groups of red-bellied tamarins (Saguinus labiatus) and maintenance of the colour vision polymorphism.

The remarkable X-linked colour vision polymorphism observed in many New World primates is thought to be maintained by balancing selection. Behavioural tests support a hypothesis of heterozygote advantage, as heterozygous females (with trichromatic vision) exhibit foraging benefits over homozygous females and males (with dichromatic vision) when detecting ripe fruit on a background of leaves. Whilst most studies to date have examined the functional relevance of polymorphic colour vision in the context of foraging behaviour, alternative hypotheses proposed to explain the polymorphism have remained unexplored. In this study we examine colour vision polymorphism, social group composition and breeding success in wild red-bellied tamarins Saguinus labiatus. We find that the association of males and females within tamarin social groups is non-random with respect to colour vision genotype, with identified mating partners having the greatest allelic diversity. The observed distribution of alleles may be driven by inbreeding avoidance and implies an important new mechanism for maintaining colour vision polymorphism. This study also provides the first preliminary evidence that wild trichromatic females may have increased fitness compared with dichromatic counterparts, as measured by breeding success and longevity.

Alleles↗
PubMed1997

Knowledge-based vision and simple visual machines.

The vast majority of work in machine vision emphasizes the representation of perceived objects and events: it is these internal representations that incorporate the 'knowledge' in knowledge-based vision or form the 'models' in model-based vision. In this paper, we discuss simple machine vision systems developed by artificial evolution rather than traditional engineering design techniques, and note that the task of identifying internal representations within such systems is made difficult by the lack of an operational definition of representation at the causal mechanistic level. Consequently, we question the nature and indeed the existence of representations posited to be used within natural vision systems (i.e. animals). We conclude that representations argued for on a priori grounds by external observers of a particular vision system may well be illusory, and are at best place-holders for yet-to-be-identified causal mechanistic interactions. That is, applying the knowledge-based vision approach in the understanding of evolved systems (machines or animals) may well lead to theories and models that are internally consistent, computationally plausible, and entirely wrong.

Animals↗
PubMed1986

Peripheral vision and child pedestrian accidents.

In both adults and children, peripheral vision is poorer than foveal vision, but there is evidence that detection in peripheral vision is relatively poorer in children than it is in adults. That may contribute to the particularly high pedestrian accident rates of children. Two laboratory experiments investigated peripheral vision in men and women and in boys and girls aged 7, 9 and 11. Using an array of stationary lights, Expt 1 examined reactions to apparent movement (the phi phenomenon) in mid and extreme periphery; and, using film sequences of a moving car, Expt 2 included a comparison of foveal and peripheral fields. Overall there was little evidence to support the hypothesis that children have poorer peripheral vision than adults relative to their foveal vision. Nonetheless there were some experimental differences: in Expt 1, 7-year-olds made fewer detections, particularly in the extreme periphery; and, in both experiments, detections tended to be slower. The relatively complex car movements in Expt 2 were detected faster in foveal than peripheral vision. There were no sex differences. Children detected more movements on the left. In Expt 2 these detections were faster, and children made relatively more simulated road crossings when the car approached from the left (all adults 'crossed' in all trials).

Accidents, Traffic↗