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Results for “Vision Tests”

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At least 991 records · Page 55Linked to original sources
PubMed2005

Deficient motion perception in the fellow eye of amblyopic children.

The extent of motion processing deficits and M/dorsal pathway involvement in amblyopia is unclear. Fellow eye performance was assessed in amblyopic children for motion-defined (MD) form, global motion, and maximum displacement (Dmax) tasks. Group performance on MD form was significantly worse in amblyopic children than in control children. Global motion deficits were significantly related to residual binocular function. Abnormally elevated Dmax thresholds were most prevalent in children with anisometropia. Our findings from these three uncorrelated tasks implicate involvement of binocular motion-sensitive mechanisms in the neural deficits of amblyopic children with strabismic, anisometropic, and aniso-strabismic etiologies.

Amblyopia↗
PubMed2006

Stereo and motion information are not independently processed by the visual system.

Many visual tasks are carried out by using multiple sources of sensory information to estimate environmental properties. In this paper, we present a model for how the visual system combines disparity and velocity information. We propose that, in a first stage of processing, the best possible estimate of the affine structure is obtained by computing a composite score from the disparity and velocity signals. In a second stage, a maximum likelihood Euclidean interpretation is assigned to the recovered affine structure. In two experiments, we show that human performance is consistent with the predictions of our model. The present results are also discussed in the framework of another theoretical approach of the depth cue combination process termed Modified Weak Fusion.

Cues↗
PubMed2006

Deficient maximum motion displacement in amblyopia.

Direction discrimination thresholds for maximum motion displacement (Dmax) are not fixed, but are stimulus dependent. Dmax increases with reduced dot probability or increased dot size. We previously reported abnormal Dmax in the fellow eyes of amblyopic children for dense patterns of small dots. To determine how deficits of Dmax in amblyopic eyes compare to those in fellow eyes, thresholds were obtained in both eyes of 9 children with unilateral amblyopia and 9 control children. The expected increase in Dmax was observed for reduced dot probability and increased dot size conditions relative to baseline in both control and amblyopic groups. Both eyes of the amblyopic group demonstrated significant deficits. Our findings implicate abnormal binocular motion processing, which may involve both low-level and high-level motion mechanisms, in the neural deficit underlying amblyopia.

Adolescent↗
PubMed2001

Analysis of the ABCR (ABCA4) gene in 4-aminoquinoline retinopathy: is retinal toxicity by chloroquine and hydroxychloroquine related to Stargardt disease?

PURPOSE: To determine if mutations in ABCR (ABCA4) are associated with chloroquine/hydroxychloroquine retinopathy. METHODS: DNA from eight patients with chloroquine or hydroxychloroquine retinopathy was studied. Controls were 80 individuals over age 65 years with normal retinal examinations. Ophthalmoscopy, color vision testing, visual fields, retinal photography, and fluorescein angiography were performed on the eight patients. Direct DNA sequencing of the exons and flanking intronic regions of the ABCR gene was completed for all patients. RESULTS: Clinical evaluation confirmed the diagnosis of chloroquine/hydroxychloroquine retinopathy and excluded Stargardt disease in each patient. Two patients had heterozygous ABCR missense mutations previously associated with Stargardt disease. None of the controls had these missense mutations. Three other patients had other missense polymorphisms. CONCLUSIONS: Some individuals who have ABCR mutations may be predisposed to develop retinal toxicity when exposed to chloroquine/hydroxychloroquine. We urge further study of a larger cohort of patients with chloroquine/hydroxychloroquine retinopathy.

ATP-Binding Cassette Transporters↗
PubMed2000

Visibility of road hazards in thermal, visible, and sensor-fused night-time imagery.

Sensor fusion combines the output of multiple imaging sensors within a single composite display. Ideally, a fused image will retain important spatial information provided by individual input images, and will convey useful spatial or chromatic emergent information derived from the contrast between input images. The present experiment assessed the potential benefits of sensor fusion as a method of enhancing drivers' night-time detection of road hazards. Observers were asked to detect a pedestrian within thermal and visible images of a night-time scene, and within chromatic and achromatic renderings created by sensor fusion of grayscale thermal and visible images. Results indicated that fusion can both improve spatial image content, and can effectively embellish spatial content with emergent chromatic information. The benefits of both sensor fusion and of color rendering, however, were inconsistent, varying substantially with quality of input images submitted for fusion.

Accidents, Traffic↗
PubMed2000

Vision standards for driving in Canada and the United States. A review for the Canadian Ophthalmological Society.

We review the vision requirements for driving with the goal of revising current Canadian Ophthalmological Society (COS) recommendations for vision standards for driving. The report comprises two sections. In the first section we report the results of a survey of transportation authorities in Canada and the United States conducted on behalf of the COS to determine the current standards and medical review procedures. The results suggest that although the standards in Canada are more consistent than those in the United States, few of the standards in either country are evidence-based. In the second section we review the recent literature on visual function and driving. We conclude from this review that adequate contrast sensitivity is as important as, if not more important than, good visual acuity for driving and that there is little evidence to support a monocular standard for acuity, contrast sensitivity or visual field. Although there is evidence that the extent of a visual field defect is related to the ability to perform driving tasks, there is little evidence to suggest a relation between the location of the visual field defect and fitness to drive.

Automobile Driving↗
PubMed1987

Evaluation of an objective method for the in vivo measurement of changes in light transmittance of the human crystalline lens.

Because the results of various vision tests and diagnostic methods are influenced by the amount of light transmitted by the lens, it would be useful to quantify changes in transmittance. We have developed a new method capable of following these changes objectively and quantitatively. The method is based on an increasing loss of fluorescence emitted by the lens substance as the probing volume is located more posteriorly along the lens axis. The loss of fluorescence is quantified by a parameter called the fluorescence reading ratio (FRR). In the present study, performed on postmortem human lenses, we evaluated the validity of our proposed in vivo method by comparing it with measurements of lens transmittance by spectrophotometry. The correlation of FRR with the transmittance between 420- and 500 nm (r greater than 0.7, P less than 0.015) indicates that the measurement of FRR can provide information on the transmittance at these wavelengths. In addition, a correlation was found between age and transmittance at 440 nm (r = 0.93, P less than 0.001) and FRR (r = 0.88, P less than 0.001).

Adult↗
PubMed1983

Visual development in infancy and childhood.

This article considers the development of vision in normal children, emphasizing new evaluative techniques that may eventually play an important role in clinical practice, and follows with a discussion of abnormal development, where recent discoveries in the laboratory and in clinical observation have already led to significant advances in the treatment of children with ophthalmologic problems.

Aging↗
PubMedDate not supplied

Dynamic retinoscopy: the missing data.

Dynamic retinoscopy is a well described but often overlooked technique that allows rapid assessment of accommodative ability. The key to the technique is the neutralization of the retinoscopic reflex that occurs when the patient accommodates on a target adjacent to the retinoscope. This clinical tool can provide critical data that can help solve treatment dilemmas, such as when a child presents with high hyperopia or when a patient presents at any age with possible accommodative insufficiency. In this review, performance of dynamic retinoscopy will be detailed, with the applicability of the technique demonstrated with use of case examples.

Accommodation, Ocular↗
PubMedDate not supplied

Early refractive development in humans.

Over recent years much interest has been directed toward understanding the process by which refractive errors develop, how this is controlled and the effect of refractive errors on subsequent visual status. There are obvious difficulties in studying such mechanisms in human subjects and for this reason many studies have employed animal models. The present paper compiles the evidence available from human subjects, examining the significance of different aspects of refractive status, normal and abnormal patterns of development and their significance in the development of normal binocular function.

Adolescent↗
PubMedDate not supplied

Does a tilted retina cause astigmatism? The ocular imagery and the retinoscopic reflex resulting from a tilted retina.

An astigmatic dial viewed by a tilted retina will have only one line in focus, simulating astigmatic blur. We compare and contrast this optical situation to actual astigmatism. Photographs were taken of an astigmatic dial blurred with a cylindrical lens, and also of the same astigmatic dial tilted, simulating tilted retinal imagery. A model eye for retinoscopy practice was provided with a retina tilted 30 degrees and was retinoscoped repeatedly with and without added confounding cylinder by five skilled retinoscopists. Photographs of the astigmatically blurred and tilted astigmatic dials were similar but not identical, as expected. The model eye with tilted retina showed no astigmatism by retinoscopy in 14/15 measurements and 0.25 D of astigmatism in one measurement. When confounding cylinder was present, the retinoscopic measurement was always within 0.25 D of the added cylinder. The ocular imagery resulting from a tilted retina can simulate astigmatic blur, but this is actually due to a type of curvature of field. Only a minute area of the tilted retina is viewed during retinoscopy, so the tilt has essentially no influence on the retinoscopic reflex.

Adult↗
PubMed2003

Early binocular vision in human infants: limitations on the generality of the Superposition Hypothesis.

The Superposition Hypothesis states that the binocular vision of newborn infants blends together the monocular visual responses of the two eyes, even when the visual stimulus evokes binocular rivalry in adults. According to the Superposition Hypothesis, this blending is replaced by binocular rivalry after the emergence of stereopsis [Neonate Cognition: Beyond the Blooming, Buzzing Confusion, Erlbaum, Hillsdale, NJ, 1985, p. 37; Early Visual Development Normal and Abnormal, Oxford University Press, New York, 1993, p. 201]. The main evidence for the Superposition Hypothesis is a preferential looking experiment [Vision Res., 26 (3) (1986) 501], in which 8-12-week-old infants fixated a rivalrous (for adults) dichoptic plaid, in preference over a fusible grating of parallel lines. This report describes our attempt to repeat that important experiment. Infant stereopsis emerged at 8.6 weeks under our conditions, but infants did not preferentially fixate the dichoptic plaid at any age between age 5 and 16 weeks. Control experiments showed that our result was not due to technical differences between their experiment and ours (red/green vs. polarizing glasses, the use of a fixation point, or the infant observation apparatus). Therefore, blending of the visual responses to rivalrous (for adults) stimuli is not a general feature of the pre-stereoptic infant visual system.

Analysis of Variance↗