SEARCH · PubMed Health

Results for “Vision Disparity”

Explore indexed PubMed citations for clinical trials, systematic reviews and public health research. Read source abstracts and follow each citation to its original PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 1,765 records · Page 98Linked to original sources

PubMed1996

Therapeutic decisions involving disparate clinical outcomes: patient preference survey for treatment of central retinal artery occlusion.

BACKGROUND: Major therapeutic decisions are made by patients with information and guidance provided by their physicians. The values patients place on different outcomes and the risks they are willing to accept are important factors in making these decisions. New beneficial therapies associated with potentially serious complications are now available for some blinding diseases. The authors aim to determine the maximum amount of risk of stroke and death persons would accept to recover vision. METHODS: Standardized survey of adults with normal vision. RESULTS: Thirty-nine percent and 37% of surveyed adults would accept some risk of stroke and death, respectively, to triple the chances of recovering 20/100 visual acuity in one eye when binocular. More than 80% of persons would accept these risks if they were monocular. Maximum risk scores were significantly higher in the monocular case scenarios than in binocular case scenarios. Medical students and eye physicians were more likely to accept risk than persons with high school or university educational backgrounds. CONCLUSIONS: The value persons place on vision when weighed against the risk of stroke or death varies considerably. More persons are willing to accept life-threatening risks if they are monocular. The reasons physicians and medical students are more likely to accept serious risks to improve vision than nonphysicians is unclear. Further studies are needed to determine how physicians' values effect the patient decision-making processes.

Adult↗

PubMed1989

Influence of mechanical disturbance on oculomotor behavior.

Using a binocular search coil technique, we measured oculomotor behavior during gentle pressing with a finger on the outer canthus of one eye. With a steadily pressed viewing eye, and the fellow eye occluded, the occluded eye deviates while the pressed eye does not. If the eye is rapidly pressed and released, the compensation of rotational force in the pressed eye becomes incomplete, so that both eyes move. At high frequencies of press (greater than 1 Hz) the pressed eye is deviated and the contralateral eye no longer moves. In darkness the pressed eye always rotates but the contralateral eye never does, demonstrating that any inflow from proprioceptors sensing rotation of the pressed eye does not affect oculomotor posture as measured in the fellow eye. With binocular viewing the results are more variable. On some trials neither eye moves, while on others both move. The results can be interpreted as a Hering's law controlled attempting to reconcile disparate inputs from the two eyes. The results confirm and extend, with objective measures, earlier conclusions from subjective experiments.

Darkness↗

PubMed1987

Vergence adaptive changes with varying magnitudes of prism-induced disparities and fusional amplitudes.

Vergence adaptation response monitored with various prism disparities demonstrated that the rates of adaptation decreased as the prismatic effect was increased. However, the amount adapted increased with the increase in the value of the prism until this value fell outside the fusional amplitude; the amount adapted then decreased. However, a large disparity can be adapted to with ease if the prismatic effect is increased gradually in small steps. The clinical implications of these results are discussed.

Adaptation, Ocular↗

PubMed1991

Health for all: a public health vision.

The approach of a millennial passage invites public health to a review of past performance and a preview of future prospects toward assuring a healthy public. Since the 1974 Canadian Lalonde report, the best national plans for health progress have emphasized disease prevention and health promotion. WHO's multinational Health for All by the Year 2000 promotes basic health services essential to leading a socially and economically productive life. Healthy People 2000, the latest US guide, establishes three goals: increase healthy life span, reduce health disparities, and achieve universal access to preventive services. Its objectives can be used to excite public understanding, equip program development, evaluate progress, and encourage public accountability for health initiatives. Needed is federal leadership in defining requisite action and securing necessary resources. Elsewhere a "new public health" emphasizes community life-style and multisectoral "healthy public policy." In the United States, a national health program is needed to achieve equity in access to personal health care. Even more essential is equitable sharing in basic health determinants in society--nutritious food, basic education, safe water, decent housing, secure employment, adequate income, and peace. Vital to such a future is able and active leadership now from governments and public health professionals.

Forecasting↗

PubMed1975

Use of random-dot sterograms in the clinical assessment of strabismic patients.

Random-dot stereograms were shown to a sample of strabismic patients for whom there was clinical evidence of stereopsis. Two kinds of sterograms were used, one of the usual sort and the other having a contour surrounding the disparate area in each field of view. The patients tested could be clearly classified as belonging to one of three response groups. The first group could fuse both kinds of stereogram, the second could fuse only he contoured kind, and the third could not fuse either kind. This grouping was found to relate to the degree to which bifoveal binocular single vision had been absent in the clinical histories of these patients. The result is discussed in terms of the consequences for vergence and stereopsis of period of absence of normal binocular function.

Adolescent↗

PubMed2005

Patterns of spectacle use in young Australian school children: findings from a population-based study.

PURPOSE: To describe the patterns of spectacle use in a population-based sample of Australian Year 1 school children (mostly aged 6 years). METHODS: Logarithm of the minimum angle of resolution (logMAR) visual acuity was measured in both eyes before and after pinhole correction, and using spectacles if worn. Cycloplegic autorefraction (cyclopentolate) and detailed dilated fundus examination were performed. Visual impairment was defined as visual acuity <40 logMAR letters (ie, <20/40 Snellen equivalent). Myopia was defined as spherical equivalent (SE) refraction < or = -0.50 diopters (D), and hyperopia as SE refraction > or = +2.0D, deemed significant when > or = +3.0D. Astigmatism was defined as cylinder > or =1.0D and anisometropia as SE refraction difference between the two eyes at least 1.0D. RESULTS: One thousand seven hundred forty predominantly 6-year-old school children were examined during 2003 to 2004. Spectacle use was documented in 77 children (4.4% of sample). Uncorrected visual impairment was found in the worse eye of 71 children (4.1%) and refractive error accounted for the majority (69.0%). Astigmatism was the most common refractive error causing visual impairment, accounting for 46.5%. Hyperopia, with or without astigmatism, was the most frequent reason for spectacle use, documented in 40.3%. Spectacle use in the absence of significant refractive error, amblyogenic risk factors, or visual impairment was noted in 26 children (33.8% of spectacle wearers). The prescription of spectacles could have benefited a further 26 children (1.5% of sample), mostly for correction of astigmatism. CONCLUSION: This study documents a significant disparity between spectacle use and need. Astigmatism was the most common cause of visual impairment due to refractive error.

Child↗

PubMed2006

Flank facilitation and contour integration: different sites.

Observers' ability to integrate features into extended contours, and to exploit the flanking structure to facilitate contrast detection (flank facilitation), exhibit a similar dependence on element spacing and orientation. Here, we investigate whether this reflects the operation of a common cortical mechanism by comparing performance for both tasks under monocular, binocular, dichoptic, and stereoscopic viewing conditions. Our results clearly implicate different cortical sites for flank-facilitated detection and contour integration; the former is a purely monocular phenomenon and must therefore occur at the earliest stages of cortical processing. In contrast, contour integration is a binocular process and occurs after the encoding of relative disparity, suggesting substantial extra-striate involvement. We conclude that the sites, and therefore the mechanisms, underlying these two seemingly related psychophysical phenomena are different.

Form Perception↗

PubMed2003

Effects of lesions of the cerebellar oculomotor vermis on eye movements in primate: binocular control.

The effects of lesions of the dorsal 'oculomotor' cerebellar vermis on binocular oculomotor functions in three monkeys were examined. Prominent findings included (1) a convergence bias during monocular fixation, i.e., an 'esodeviation' in the absence of disparity cues, (2) a loss of comitancy, i.e., alignment varies more with orbital position, (3) abnormal saccade yoking producing saccade disconjugacy, and (4) defects in prism-induced phoria adaptation. There was also a suggestion of a disturbance in the dynamic properties of disparity-induced vergence. These findings point to a role for the 'oculomotor' vermis in binocular aspects of the control of eye movements.

Adaptation, Physiological↗

PubMed2007

Disparities in pediatric preventive care in the United States, 1993-2002.

OBJECTIVES: To quantify physician-reported preventive counseling and screening during well-child visits (WCVs) and to examine racial and ethnic disparities in these activities. DESIGN: Cross-sectional study using the National Ambulatory Medical Care Survey, January 1993 through December 2002. SETTING: Office-based physician practices. PARTICIPANTS: Children from birth to 18 years old who were seen by a physician for a WCV. MAIN OUTCOME MEASURE: Preventive counseling and screening. RESULTS: Well-child visits were shorter for Latino children than for white or black children. At WCVs, white children were more likely to receive preventive counseling than were black or Latino children (72% vs 61% vs 61%, respectively; P = .01) but not more likely to receive screening for elevated blood pressure, anemia, vision and hearing acuity, or lead toxicity. There were no differences in secondary diagnoses made at WCVs for white, black, or Latino children (15% vs 17% vs 14%, respectively; P = .65). The children who received the least counseling were Latino children in the public sector non-health maintenance organization setting (counseled at 39% of visits) and Latino children who self-paid for the visits (counseled at 26% of visits). After adjusting for possible confounders, including medications prescribed at the visit, black and Latino children were less likely to receive counseling than were white children (odds ratios, 0.68 and 0.63; 95% confidence interval, 0.48-0.97 and 0.44-0.90, respectively), and black children were less likely to receive preventive screening services (odds ratios, 0.65; 95% confidence interval, 0.45-0.93). CONCLUSIONS: By physician report in a nationally representative sample, black and Latino children received less counseling at WCVs than did white children. These disparities were unexplained by the competing demands of other secondary diagnoses or medications prescribed or dispensed.

Adolescent↗

PubMed1980

The double-nail illusion: experiments on binocular vision with nails, needles, and pins.

When two nails or similar slender objects are held straight ahead at reading distance, one a few centimetres behind the other and aligned at the same eye level, they are seen side by side rather than one behind the other. A quantitative study of this 'double-nail' illusion shows that the objects are judged to be at the positions of the so-called apparent or ghost images known from fusional theories of stereopsis. Most recent fusional theories assume that apparent images are suppressed by neuronal interactions, and the usual absence of percepts corresponding with apparent images is often quoted as an argument against 'projection' theories of stereopsis. The double-nail illusion shows, however, that percepts which correspond with apparent images do occur. The results are interpreted in terms of a neuronal-network type of fusional theory, in which the interpretation that corresponds with the minimum overall disparity is assumed to dominate. The following parameters were varied in the experiments: length, width, colour, and contrast for each of the nails; and fixation point position; and the orientation of the nail carrier. The results show that identity of the stimuli is not a necessary condition for the illusion. A stable vergence can be enforced by the double-nail illusion, and with additional nails multistable states of vergence can be obtained.

Color↗

PubMedDate not supplied

Assessment of stereopsis in rhesus monkeys using visual evoked potentials.

Rhesus monkeys can have deficiencies in stereo vision, making it necessary to screen monkey subjects intended for single cell studies of stereo-based depth processing. We measured VEPs in two monkeys using a dynamic random-dot display in which a stereo-defined checkerboard reversed in depth. Monkeys fixated upon a small dot during stimulus presentation. One monkey showed clear evoked potentials in response to changes in disparity that were similar to those obtained in human subjects, using an identical stimulus paradigm. Controls with presentations of the monocular stimulus sequences (in which no depth reversal can be perceived) yielded no or much weaker VEPs. In the other animal, however, there was no difference in evoked potential between the two conditions. These electrophysiological findings closely match the performance of these same two subjects in a disparity discrimination task in which they were previously trained. We conclude that VEPs using this type of stimulus display can be used to screen monkeys for single cell or behavioral studies of stereopsis.

Animals↗

PubMed1997

[Binocular functions in amblyopia and strabismus].

Regarding the changing trends in the concept, definition, etiological classification, and criteria for diagnosis of amblyopia, we reviewed a total of 4,693 cases of amblyopia seen during the past 37 years. The amblyopia was divided into four types: strabismic, anisometropic, ametropic, and form vision deprivative. There was a definite trend for the incidence to decrease and for the diagnosis to be made during earlier age in recent years. Although favorable recovery of visual acuity is obtained after treatment of amblyopia and strabismus, there are difficulties in obtaining good binocular functions in early-onset amblyopia and strabismus. This feature was evaluated in regard to motion perception asymmetry (MPA) and binocular depth from motion (DFM). Many cases of early-onset amblyopia and strabismus showed no disparity stereopsis, or position stereopsis, in spite of the presence of DFM. The MPA appeared to be closely related to early-onset esotropia regardless of age, while it disappeared and motion perception became symmetric 4 to 5 months after birth in normal infants. The DFM seemed to play an important role in maintaining good motor alignment for several years after surgery. I developed a checkerboard pattern stimulator in 1978. This method proved to be useful in developing binocular functions and motor alignment by applying simultaneous bifoveolar stimulation and anti-suppression. Extensive exposure to the stimulation was essential for therapeutic success.

Adolescent↗

PubMed1994

Why two eyes are better than one for judgements of heading.

Are two eyes needed for judging direction of self-motion? Traditional analyses stress that the pattern of optic flow in one eye is sufficient. The main difficulty is how to deal with the eye or head rotation. Extraretinal signals help, but humans can also discount the effect of rotation purely on the basis of monocular flow provided the scene contains depth. Depth differences give rise to changing binocular disparities when the observer moves. These disparities are ignored in monocular theories of judgements of heading. Using computer generated displays, we investigated whether stereoscopic presentation improves heading judgements for conditions that pose problems to the monocular observer. We found that adding disparities to simulated ego-motion through a cloud of dots made heading judgements up to four times more tolerant to motion noise. The same improvement was found when the disparities specify the initial distances throughout the motion sequence. We conclude that binocular disparities improve judgements of heading by imposing a depth order on the elements of the scene, not because they provide additional information on the elements' motion in depth.

Depth Perception↗

PubMed1980

Modifications of the classical notion of Panum's fusional area.

It is generally believed that there is an absolute disparity limit for binocular fusion; objects with disparities within this limit, known as Panum's fusional area, will appear fused and single, while objects with disparities outside the limit appear double. It is demonstrated, however, that the disparity gradient, rather than the disparity magnitude, dictates binocular fusion when several objects occur near one another in the visual field. The disparity gradient is defined as the difference between the disparities of neighboring objects divided by their angular separation. If this ratio exceeds a critical value (approximately 1) then fusion does not occur, even though the absolute disparities of the individual objects may be well within the classical Panum's area. This discovery leads to the reinterpretation of several enigmatic phenomena in stereopsis, including Panum's limiting case.

Humans↗

PubMed1995

A quantitative and qualitative assessment of the Solitaire Bifocal Contact Lens.

We performed qualitative and quantitative assessments of contact lens performance at 1 and 6 months among 23 patients enrolled in the Solitaire Bifocal Contact Lens Study. Overall satisfaction and comfort at 6 months was rated good to excellent in 83% and 84% of patients, respectively. Daytime acuity at distance and near were rated very good to excellent in 75% and 83% of subjects. Quantitative measurements of distance and near acuities at 1 month revealed 83% and 88% of subjects, respectively, seeing better than or equal to 20/25 or J1. At 6 months there was a moderate decrease in the measured distance acuity. A disparity in glare disability was noted, with 53% of subjects indicating significant glare problems but only 21% of glare tested patients having acuities worse than 20/40. Attrition from the study was highest in the first month and was more common among first-time contact lens users. Overall, this segmented bifocal contact lens is well-tolerated and provides good distance and near vision for presbyopic patients.

Accommodation, Ocular↗

PubMed1989

Human optokinetic nystagmus is linked to the stereoscopic system.

It was previously proposed that a linkage between the optokinetic system and the stereoscopic system in higher mammals serves to allow these animals to selectively stabilize those parts of the visual scene which lie in the plane of convergence as the animals move forward in a three-dimensional world (Howard and Ohmi, 1984). A new procedure is now described by which OKN gain can be measured as a function of the binocular disparity of the stimulus. With vergence locked on a vertical line, the gain of the slow phase of vertical optokinetic nystagmus (OKN) was recorded in four human subjects as the binocular disparity (stereo depth) of the moving display was changed from -3 degrees to +3 degrees. The gain of OKN was found to be inversely proportional to binocular disparity. Evidence for cells in the visual cortex, MT and MST that are sensitive both to visual motion and binocular disparity is reviewed. It is argued that the activity of cells responsive to direction of motion and zero disparity selectively augments OKN and that this enables humans to stabilize the images of parts of the scene in the plane of regard while ignoring competing motion signals arising from other distances.

Functional Laterality↗

PubMed1993

Cell responses to vertical and horizontal retinal disparities in the monkey visual cortex.

Because of the horizontal separation of both ocular globes, the projection angles are slightly different. These differences are commonly termed retinal disparities. Vertical and horizontal retinal disparities occur constantly in normal life. We have investigated the responses of single cells in cortical areas V1 and V2 of behaving Macaca mulatta monkeys to retinal disparities by using dynamic random dot stereograms. Our findings show that cortical visual cells are sensitive to both vertical and horizontal disparities. To calculate the distance between two objects in a three-dimensional space from horizontal disparities, it is necessary to know the fixation distance. It has been suggested that the horizontal gradient of vertical disparity contains information to estimate the fixation distance and therefore to scale horizontal disparities. We suggest that these cells sensitive to horizontal and vertical disparities represent a neural mechanism that provides information to the visual system in order to achieve a correct eye alignment and depth perception.

Animals↗

PubMed2003

Modification of depth and distance perception caused by long-term wearing of left-right reversing spectacles.

For 35 to 39 days, four observers wore continuously left-right reversing spectacles which pseudoscopically reverse the order of binocular disparity and direction of convergence. In three tests, we investigated how the visual system copes with the transformation of depth and distance information due to the reversing spectacles. In stereogram observation, after a few days of wearing the spectacles. the observers sometimes perceived a depth order which was opposite to the depth order that they had perceived in the pre-spectacle-wearing period. Monocular depth cues contributed more to depth perception in the spectacle-wearing period than they did in the pre-spectacle-wearing period. While the perceived distance significantly decreased during the spectacle-wearing period, we found no evidence of adaptive change in distance perception. The results indicate that the visual system adapts itself to the transformed situation by not only changing the processing of disparity but also by changing the relative efficiency of each cue in determining apparent depth.

Adaptation, Physiological↗