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PubMed2000

Healthy People 2010--vision objectives for the nation.

BACKGROUND: In January 2000, the U.S. Department of Health and Human Services released new national health goals and objectives in a report entitled Healthy People 2010. This national report includes specific objectives for improving the vision of people in the United States during the 2000-2010 decade through prevention, early detection, treatment, and rehabilitation. The vision objectives, along with other health objectives, are designed to help the nation achieve two major outcomes: (1) increase the quality and years of healthy life and (2) eliminate health disparities among different groups. These health objectives will strongly influence many health care programs and the provision of health care through laws, regulations, reimbursements, and clinical guidelines enacted by federal and state agencies. PURPOSE: The purpose of this article is to inform optometrists about the new Healthy People 2010 vision objectives. METHODS: A summary of the Healthy People process for developing the objectives--and the specific vision objectives--is provided. These objectives address many important areas, including: regular dilated eye examinations; vision screening for preschool children; uncorrected visual impairment due to refractive errors; blindness and visual impairment in children and adolescents; visual impairment due to diabetic retinopathy, glaucoma, and cataracts; occupational eye injury; the use of personal protective eye wear in recreational activities and hazardous situations around the home; and the use of vision rehabilitation services and adaptive devices by people with visual impairments. CONCLUSION: These new national health goals and objectives will impact optometrists. Therefore, it is important that optometrists understand these objectives and actively work to help implement them at the national, state, and local levels. By doing this, they can help provide the services needed to reduce visual impairments and improve the vision of people in their communities.

Health Promotion↗
PubMed1996

Sequential stereopsis: a simple demonstration.

Most people strongly prefer to use back-and-forth eye movements in order to discriminate 3-dimensional distances among targets that are widely separated from each other in direction. This viewing strategy permits sequential stereopsis: a comparison between the foveally-seen pre-saccadic disparity of one target with post-saccadic disparity of the other. This note describes a simple and qualitatively compelling demonstration of the usefulness of sequential stereopsis, in a situations in which classical stereopsis, with steady fixation, is greatly degraded. Targets of high-spatial-frequency texture are used, with details that can be resolved foveally before and after saccades, but that are unresolvable in peripheral vision. Back-and-forth eye movements between such textured targets, separated by 8-10 deg from each other, led to estimates of threshold that average less than 45 sec arc disparity (corresponding to about 0.18% of viewing distance): some of the best performances ever reported for targets so widely separated.

Adolescent↗
PubMed1999

Binocular vision enhances phase discrimination by filtering the background.

Previous studies have shown that the detectability of a noise-masked target can be enhanced under stereoscopic viewing when the target's interocular disparity differs from that of the noise. This enhanced detectability can be accounted for by a model postulating that the binocular system linearly sums the left-eye and right-eye views of a visual scene. This model also predicts enhanced phase discrimination under specifiable interocular disparities of target and noise. Two experiments were conducted in which subjects were asked to discriminate between two luminance patterns (target and foil) that differed only in phase. The target patterns were constructed by summating two vertical sinusoidal gratings in which the phase difference between the higher and the lower spatial frequency gratings was 45 degrees. The foils contained the same two component frequencies, with a phase difference of -45 degrees. Thus, targets and foils were mirror images of one another. The ability of subjects to discriminate between these stereoscopically viewed mirror-image patterns was investigated under two sets of interocular disparities: those that, according to our model, would unmask one or both spatial frequency components, and those that would leave both components masked by the noise. Phase discrimination was enhanced only when both component frequencies of the target and foil were unmasked. The implications of these findings for template-matching and phase-discrimination models of pattern discrimination are considered.

Female↗
PubMed1992

Functional binocular vision is not dependent on visual experience in the praying mantis.

In vertebrates, it has been shown that binocular visual experience is necessary to develop normal spatial vision. We have investigated whether this is also true for an invertebrate, the praying mantis. The praying mantis is a predatory insect in which prey localization involves the use of binocular disparities. We raised mantids which had one eye occluded throughout development and tested monocular visual fixation and binocular distance estimation in the adult animals. The results revealed that both fixation and prey catching behavior were normally functional in the monocularly reared animals. Thus we conclude that, in mantids, binocular vision is based on a fixed mode of development.

Animals↗
PubMed1980

[Decreasing local stereopsis with increasing horizontal disparity, indicating decreasing density of binocular cortical projection towards the limits of Panum's area (author's transl)].

Measuring local stereopsis by means of random dot stereograms with increasing horizontal disparity, the relative density of binocular cortical projection has been determined at a distance of 75 min of arc from the fovea. The accuracy of stereoscopic perception decreased with increasing horizontal disparity. The reciprocal value of the error frequency was used to measure the density of binocular cortical projection. Panum's area at the above mentioned distance from the fovea can be constructed by plotting the error frequency against the horizontal disparity. We observed a decrease of the relative density of binocular cortical projection towards the limits of Panum's area without a sharp break. The results are in agreement with those reported by Bishop and Henry and Joshua in the cat (receptive field disparity). The theory of stereopsis as proposed by Bishop explains our findings well and may be transferred to binocular vision in man.

Depth Perception↗
PubMed2005

Who is playing doctor? -- The gap between self-perceived versus professionally diagnosed chronic conditions among the underserved minority.

OBJECTIVE: To assess the gap between self-perceived and professionally diagnosed physical and mental conditions in underserved minority populations. STUDY SETTING: The study sample consisted of 287 African-American and Latino heads of households respondents, obtained from a geographically defined random sample of 418 households from three Urban Public Housing Communities in Los Angeles County, California. STUDY DESIGN: This study conducted a cross-sectional survey with face-to-face interviews. RESULTS: Eighty-five percent (245) of this sample reported that they were suffering from at least one chronic condition. However, 43% of participants who suffer from chronic condition(s) claimed that a physician had never diagnosed at least one of their chronic illnesses. Depression (16%), hearing impairment (10%), arthritis (8%), dental problems (7%), and vision conditions (7%) are the most frequently reported undiagnosed chronic conditions among these populations. CONCLUSION: This study documents significant disparities in the detection and treatment of specific medical conditions among Hispanic and African-American population residing in public housing, which often leads to end-stage complications due to lack of timely diagnoses and treatment.

Adult↗
PubMed1998

Complex visual hallucinations. Clinical and neurobiological insights.

Complex visual hallucinations may affect some normal individuals on going to sleep and are also seen in pathological states, often in association with a sleep disturbance. The content of these hallucinations is striking and relatively stereotyped, often involving animals and human figures in bright colours and dramatic settings. Conditions causing these hallucinations include narcolepsy-cataplexy syndrome, peduncular hallucinosis, treated idiopathic Parkinson's disease, Lewy body dementia without treatment, migraine coma, Charles Bonnet syndrome (visual hallucinations of the blind), schizophrenia, hallucinogen-induced states and epilepsy. We describe cases of hallucinosis due to several of these causes and expand on previous hypotheses to suggest three mechanisms underlying complex visual hallucinations. (i) Epileptic hallucinations are probably due to a direct irritative process acting on cortical centres integrating complex visual information. (ii) Visual pathway lesions cause defective visual input and may result in hallucinations from defective visual processing or an abnormal cortical release phenomenon. (iii) Brainstem lesions appear to affect ascending cholinergic and serotonergic pathways, and may also be implicated in Parkinson's disease. These brainstem abnormalities are often associated with disturbances of sleep. We discuss how these lesions, outside the primary visual system, may cause defective modulation of thalamocortical relationships leading to a release phenomenon. We suggest that perturbation of a distributed matrix may explain the production of similar, complex mental phenomena by relatively blunt insults at disparate sites.

Brain Diseases↗
PubMed1980

Fusional vergence: sustained and transient components.

There is evidence to suggest that fusional vergence acts as a two-stage process consisting of fusion-initiating and fusion-sustaining components. The interrelationship of these components was examined by comparing the amplitude of disparity-induced vergence over the operating range of sustained fusional vergence. The results showed that as sustained convergence increased, disparity-induced divergence increased and disparity-induced convergence remained essentially constant. These results are interpreted as indicating independence between the components and that the obtained increase in disparity-induced divergence resulted from an influence of accommodation on uncrossed retinal disparities.

Accommodation, Ocular↗
PubMed1997

The Pulfrich effect and its relationship to retinal illumination.

The Pulfrich stereo-illusion effect occurs in patients with monocular anterior visual system disease when viewing a pendulum. It also can be induced by placing a monocular neutral-density filter in a normal subject. We studied 10 normal subjects to determine if the Pulfrich effect could be induced by monocular illumination in addition to monocular neutral-density filtration. Eighteen of 20 eyes observed the Pulfrich effect with monocular illumination, but the rotation of the ellipse was opposite in direction to that of the neutral-density filter. Our data suggests that the Pulfrich effect results from intereye luminance disparity.

Female↗
PubMed2005

Neural mechanisms of three-dimensional vision.

We can see things in three dimensions because the visual system re-constructs the three-dimensional (3D) configurations of objects from their two-dimensional (2D) images projected onto the retinas. The purpose of this paper is to give an overview of the psychological background and recent physiological findings concerning three-dimensional vision. Psychophysical and computational studies have suggested that in the visual system the 3D surface orientation is first estimated independently from individual depth cues--such as binocular disparity, as well as various monocular cues including texture gradients--and then the information from these different depth cues is integrated to construct a generalized representation of the 3D surface geometry. Neurons involved in low-level disparity processing, or the detection of local absolute disparity, were found mainly in the occipital cortex, whereas neurons involved in high-level disparity processing, or the reconstruction of 3D surface orientation through the computation of disparity gradients, were found mainly in the parietal area caudal intraparietal sulcus (CIP). Neurons sensitive to texture gradients, which is one of the major monocular cues, were also found in CIP. The majority of these neurons were sensitive to disparity gradients as well, suggesting their involvement in the computation of 3D surface orientation. In CIP, neurons sensitive to multiple depth cues were widely distributed together with those sensitive to a specific depth cue, suggesting CIP's involvement in the integration of depth information from different sources. In addition, human and monkey imaging studies have indicated convergence of multiple depth cues in CIP. These neurophysiological findings suggest that CIP plays a critical role in 3D vision by constructing a generalized representation of the 3D surface geometry of objects.

Animals↗
PubMed1987

Serial and parallel search in pattern vision?

The nature of the processing of combinations of stimulus dimensions in human vision has recently been investigated. A study is reported in which visual search for suprathreshold positional information--vernier offsets, stereoscopic disparity, lateral separation, and orientation--was examined. The initial results showed that reaction times for visual search for conjunctions of stereoscopic disparity and either vernier offsets or orientation were independent of the number of distracting stimuli displayed, suggesting that disparity was searched in parallel with vernier offsets or orientation. Conversely, reaction times for detection of conjunctions of vernier offsets and orientation, or lateral separation and each of the other positional judgements, were related linearly to the number of distractors, suggesting serial search. However, practice has a significant effect upon the results, indicative of a shift in the mode of search from serial to parallel for all conjunctions tested as well as for single features. This suggests a reinterpretation of these and perhaps other studies that use the Treisman visual search paradigm, in terms of perceptual segregation of the visual field by disparity, motion, color, and pattern features such as colinearity, orientation, lateral separation, or size.

Attention↗
PubMed1982

Control theory approach to accommodation and vergence.

A control theory model that treats the accommodative system and the vergence system each as negative feedback systems is investigated. The effects of accommodative vergence and vergence accommodation are included. The controllers in this model are assumed to be linear time-invariant operators. Only time-independent stimuli are considered. If vergence accommodation is neglected, the model is consistent with classical graphical analysis. By including vergence accommodation, several important changes occur. Disparity vergence is not, in general, equal to the dissociated phoria. The shape of the zone of single, clear, binocular vision is changed. Instabilities in the system arise.

Accommodation, Ocular↗
PubMed1969

Binocular depth discrimination and the nasotemporal division.

1. If classical partial decussation exactly segregates the projections of right and left hemi-retinae on to the two optic tracts, the images of an object in central vision, nearer or further than the fixation point, should project to separate hemispheres. This would prevent the encoding of retinal disparity by binocularly driven neurones of the visual cortex.2. It is proposed that there is a central vertical strip of retina in each eye which is represented in both hemispheres. The angular width of this strip should be exactly one half the actual range of horizontal disparities of binocular receptive fields near the central vertical meridian.3. By recording from single neurones in the area 17/18 region in both hemispheres of a cat, it was found that there is such a strip of bilateral projection. The centres of receptive fields for units from the two hemispheres overlap in the middle of the visual field by about 1.5 degrees and the S.D. of the distribution is about 0.5 degrees .4. The horizontal disparities of the centres of binocular receptive fields were measured for samples of units representing different parts of the visual field. The range of horizontal disparity for fields near the area centralis is about 2.3 degrees , the S.D. of the distribution about 0.9 degrees . The proposed relationship between bilateral projection and disparity coding is thus confirmed.5. The origin of the bilateral projection is a matter of speculation, but in the cat some of it is almost certainly due to imprecision in the nature of the nasotemporal division of optic nerve fibres at the optic chiasma. A case can be made, however, that the overlap is partly due to connexions through the corpus callosum between the two occipital lobes.6. Evidence for the importance of the callosal pathway in man is drawn from the effects on stereopsis of section of the chiasma and the callosum.

Animals↗
PubMed2003

A vision for cancer incidence surveillance in the United States.

A comprehensive framework for cancer surveillance should span the entire lifespan and be capable of providing information on risk, burden, disparity, cost, cancer care, survival, and death. Cancer incidence, the point in the continuum when an individual is diagnosed with cancer, has a strong, well-developed system to produce information about newly diagnosed cancer cases. However, in the future, this system must be enhanced and integrated with other cancer surveillance networks and other systems to provide timely information on the burden of newly diagnosed patients with respect to various cross-cutting population characteristics (e.g., social, economic, race/ethnic, urbanicity, or access to care) to define, monitor, and reduce incidence and various disparities noted among population groups. Collaboration in data collection, standard setting, surveillance activities, research, education and training, data use, and advocacy among all registries and national programs will be important to the continued success of the cancer incidence surveillance system. The cancer registry is an integral part of the infrastructure to reduce the burden of cancer, including the numbers of newly diagnosed cases.

Forecasting↗
PubMed1977

Anomalies of disparity detection in the human visual system.

1. Oculomotor and psychophysical depth responses were investigated in thirty individuals by use of briefly exposed disparities in the range from 0-6 to 4-6 degrees (1-8 centrads). 2. The results substantiate a previous finding which reported the common occurrence of specific types of stereoanomalies within a sample from the normal population. However, arguments are presented to suggest that these forms of stereoanomalies are limited to coarse stereopsis and spare mechanisms concerned with fine disparity, high resolution stereopsis. 3. A relatively high proportion of individuals were found to manifest deficiencies of vergence eye movement under these stimulus conditions. These vergence-anomalies are characterized by a marked reduction, or absence, of neither convergent or divergent eye movements to briefly exposed stimuli. 4. The vergence-anomaly is not detrimental under normal seeing conditions since it can be present in persons with adequate binocular vision and normal fine stereopsis. 5. The presence of vergence-anomaly was always associated with the occurrence of stereoanomaly; however, the converse was not true. 6. The results are taken as evidence to show how disparity information is organized prior to its influence upon the processes of coarse stereopsis and vergence initiation.

Depth Perception↗