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PubMed1998

The influence of vision on the automatic postural muscle responses of newly standing and newly walking infants.

In adults, visual inputs do not appear to contribute significantly to automatic postural muscle responses (90-100 ms latency) activated by transient support surface displacements causing threats to standing balance, but are activated through slow pathways with latencies of more than 200 ms. However, it has been shown that the postural sway behavior of early walking infants is strongly influenced by visual flow cues that falsely signal self-movement. To determine whether there also are significant contributions of vision to automatic postural muscle responses in this age group, two groups of infants were tested on a moveable platform; pre-walkers (n=6) and early walkers (n=6). Pre-walkers did not show any measurable effect of visual condition (vision vs no vision) on muscle response characteristics. However, the integrated gastrocnemius activity of early walkers increased significantly in vision versus no vision conditions (P<0.05). These results show that visual cues contribute to, or modulate, the automatic postural responses in children who are in the developmental transition to independent walking.

Cues↗
PubMed1999

How do general practitioners diagnose and manage patients with transient monocular loss of vision of sudden onset?

Symptoms of transient loss of vision in one eye differ widely. They may have different causes and therefore carry a different prognosis. We studied the influence of differences between characteristics of transient monocular blindness on the diagnosis and management by general practitioners (GPs). A postal questionnaire, was sent to 1600 GPs in The Netherlands along with four case vignettes describing a case history of a 56-year-old man with transient monocular disturbances of vision of sudden onset. We introduced random permutations in the following four elements of the history: partial or complete visual field involved, blurring or blacking out of vision, attacks lasting minutes or hours, and patients having covered either eye during the attack or not. Respondents were asked about the probable diagnosis and the preferred management. For each of the 16 permutations about 50 responses were obtained (overall response rate 54%). Ischemic transient monocular blindness (ITMB) was chosen as the most likely diagnosis in 49%. In 12% primary ocular disease was suspected. Involvement of the complete visual field, blacking out of vision, and short attacks were identified as independent predictors of a diagnosis of ITMB. A diagnosis of ITMB would have resulted in referral to a specialist in 72% of patients. Antithrombotic treatment would have been initiated in only 36% of ITMB patients. GPs consider brief attacks with complete blacking out of vision most typical for retinal ischemia. They refer only three-quarters of patients with probable ITMB to a specialist and start antithrombotic medication in only one-third of these patients. Therefore further education with regard to transient monocular blindness is needed.

Amaurosis Fugax↗
PubMed2006

Evaluation of cross-sectional and longitudinal construct validity of two vision-related quality of life questionnaires: the LVQOL and VCM1.

The Low Vision Quality of Life (LVQOL) questionnaire and the Vision-related Quality of Life Core Measure (VCM1) are two of the many vision-related quality of life (QOL) questionnaires that have been developed in recent years. Although psychometric properties of the LVQOL and VCM1 compare well with other vision-related QOL questionnaires, construct and longitudinal validity have not been assessed (adequately). The purpose of this study was to examine the cross-sectional and longitudinal construct validity of these questionnaires by testing specific pre-specified hypotheses about the relations of these questionnaires with other measures. The percentage of hypotheses regarding the cross-sectional construct validity that were refuted for the LVQOL was 22% for the basic aspects of vision subscale, 50% for the mobility subscale, 39% for the adjustment subscale and 17% for the reading and fine work subscale. For the VCM1 this percentage was 57%. For the longitudinal construct validity the percentage of hypotheses that were refuted ranged from 33 to 75% for the LVQOL subscales and was 50% for the VCM1. In conclusion, cross-sectional construct validity was satisfactory for the LVQOL subscales, but seemed poor for the VCM1. In addition, the longitudinal validity of these scales was poor to moderate.

Aged↗
PubMed1994

Clinical testing of the Ultra-Vision screen-film system for maxillofacial radiography.

The Ultra-Vision screen (Du Pont, Towanda, Pa.) contains a yttrium tantalate phosphor-emitting ultraviolet light and eliminates the crossover effect. Increased resolution has been proven in vitro and the purpose of the present study was to test these findings in a clinical situation. Fifteen pairs of skull radiographs were produced with the use of Du Pont Ultra-Vision Rapid screens and Kodak Lanex (Eastman Kodak, Rochester, N.Y.) screens both belonging to speed class 400. Objects were a cadaver head, a 3M phantom head (3M Corp., St. Paul, Minn.), and patients who were serially radiographed as controls in a dental implant study. The radiographs had identical densities, but contrast was varied deliberately. Twelve observers judged the radiographs blindly. Ninety-two percent of the ratings with respect to resolution favored the Ultra-Vision system. However, great doubt was expressed regarding contrast. The agreement between the observers was tested by a Cochran's Q test. The results confirm that the Ultra-Vision system exhibits an improved resolution compared with the Lanex system. Ultra-Vision is recommended whether improved resolution of the radiographs or an expected reduced patient dose is preferred.

Dental Implants↗
PubMed1984

Within-species variations in visual capacity among squirrel monkeys (Saimiri sciureus): color vision.

Color vision was studied in 27 squirrel monkeys (Saimiri sciureus) of Peruvian origin (Roman Arch variety). Tests of wavelength discrimination and Rayleigh matching as well as a search for a spectral neutral point were carried out in a behavioral paradigm involving a three-alternative, forced-choice discrimination. Significant individual variations in color vision were found in this species. Some squirrel monkeys have trichromatic color vision, others are dichromats. Within each of these catagories there appear to be three subtypes. Each of these color vision phenotypes can be interpreted as reflecting the presence of a different combination of the types of cone photopigments known to characterize this species. There is a striking gender difference in squirrel monkey color vision; whereas both trichromatic and dichromatic female monkeys were found, all of the males tested were dichromats.

Animals↗
PubMed1987

Positional uncertainty in peripheral and amblyopic vision.

Three experiments were performed to examine positional acuity and the role of spatial sampling in central, peripheral and amblyopic vision. In the first experiment, 3-line bisection acuity was compared to grating acuity. In normal foveal vision bisection acuity represents a hyperacuity. In anisometropic amblyopes, bisection acuity is reduced in rough proportion to their grating acuity. In strabismic amblyopes, and in the normal periphery, bisection acuity is reduced to a greater extent than grating acuity. This result implies that reduced contrast sensitivity of the spatial filters is not sufficient to account for the increased positional uncertainty found in peripheral vision and in strabismic amblyopia. In order to test the hypothesis that the high degree of positional uncertainty evident in these visual systems is a consequence of sparse spatial sampling, bisection thresholds and width discrimination thresholds were measured with stimuli comprised of discrete samples. The results showed that normal foveal vision and the vision of anisometropic amblyopes show little benefit from adding discrete samples to the stimulus. In contrast, the normal periphery, and the central field of strabismic amblyopes demonstrate marked positional uncertainty which can be efficiently reduced in proportion to the square root of the number of samples (up to about 10) comprising the stimulus in the direction orthogonal to the discrimination cue. In aggregate the results suggest that anisometropic and strabismic amblyopia are fundamentally different. The positional uncertainty in anisometropic amblyopia is consistent with the reduced sensitivity of the spatial filters. The data of the normal periphery and of the central field of strabismic amblyopes suggest that the cortical sampling grain imposes a fundamental limit upon their positional acuity.

Amblyopia↗
PubMed1990

Development of visual sensitivity to light and color vision in human infants: a critical review.

The recent literature on test threshold and color vision in human infants is critically reviewed. Test thresholds are higher in infants than in adults at the absolute threshold and at all adapting luminances, but approach adult values rapidly over the first six months of life. The spectral luminous efficiency function of infants is similar to V(lambda) above 1.0 log phot. cd/m2. For lights below about 1.0 log scot. cd/m2 and wavelengths shorter than 590 nm, the luminous efficiency function is similar to V'(lambda). The luminous efficiency of any given stimulus may differ markedly between infants and adults, especially when the adult data depend on the temporal and spatial parameters of the stimuli. Color vision improves greatly over the first three postnatal months, and most normal 3-month olds have at least some color vision. The overall insensitivity of infants to contrast is likely to provide a satisfactory explanation of the poor color vision of infants. The critical immaturity primarily responsible for the high thresholds and poor color vision of infants is probably after the site of visual adaptation, although lower-level factors may also play a role.

Adaptation, Ocular↗
PubMed1994

Molecular basis for color vision.

Amino acid sequences of four kinds of chicken cone pigments and two kinds of nocturnal gecko visual pigment were determined. Calculations of amino acid identities indicate that gecko pigments should be cone pigments. A phylogenetic tree of visual pigments constructed demonstrated that cone pigments evolved earlier than rod pigments (rhodopsins), indicating that daylight vision including color vision appeared earlier than twilight vision. The divergence of cone pigments to rhodopsins would be caused by replacing basic amino acid residues to acidic ones according to net charge calculations. A comparison between chicken rhodopsin and cone pigments (chicken green and red) displayed that the cone pigments are faster in regeneration from 11-cis retinal and opsin, faster in formation of meta II-intermediate and shorter in lifetime of meta II-intermediate than rhodopsin. These facts would partly explain the rapid dark adaptation, the rapid light response and the low photosensitivity of cones compared with rods. In comparison with di- and tri-chromatic color visions, chicken tetra-chromatic vision was discussed on the basis of both absorption spectra of cone pigments and filtering effect of oil droplets.

Animals↗
PubMed2006

Treated amblyopes remain deficient in spatial vision: a contrast sensitivity and external noise study.

To evaluate residual spatial vision deficits in treated amblyopia, we recruited five clinically treated amblyopes (mean age=10.6 years). Contrast sensitivity functions (CSF) in both the previously amblyopic eyes (pAE; visual acuity=0.944+/-0.019 MAR) and fellow eyes (pFE; visual acuity=0.936+/-0.021 MAR) were measured using a standard psychophysical procedure for all the subjects. The results indicated that the treated amblyopes remained deficient in spatial vision, especially at high spatial frequencies, although their Snellen visual acuity had become normal in the pAEs. To identify the mechanisms underlying spatial vision deficits of treated amblyopes, threshold vs external noise contrast (TvC) functions--the signal contrast necessary for the subject to maintain a threshold performance level in varying amounts of external noise ("TV snow")--were measured in both eyes of four of the subjects in a sine-wave grating detection task at several spatial frequencies. Two mechanisms of amblyopia were identified: increased internal noise at low to medium spatial frequencies, and both increased internal noise and increased impact of external noise at high spatial frequencies. We suggest that, in addition to visual acuity, other tests of spatial vision (e.g., CSF, TvC) should be used to assess treatment outcomes of amblyopia therapies. Training in intermediate and high spatial frequencies may be necessary to fully recover spatial vision in amblyopia in addition to the occlusion therapy.

Adolescent↗
PubMed1999

Spatial and temporal vision in patients treated for bilateral congenital cataracts.

Using the method of limits, we measured spatial and temporal vision in 13 children who had been deprived of patterned visual input during infancy until they were treated for dense central cataracts in both eyes. Spatial vision was assessed with vertical sine-wave gratings, and temporal vision was assessed with an unpatterned luminance field sinusoidally modulated over time. Under these testing conditions, spatial contrast sensitivity at low and medium spatial frequencies (0.33-2 c deg-1) was within normal limits, but sensitivity at higher spatial frequencies and grating acuity were reduced on average by 1.3 and 0.5 log units, respectively. Temporal vision was affected less severely, with losses in sensitivity only for low temporal frequencies (5 and 10 Hz), which averaged 0.4 log units. Thus, spatial and temporal vision are likely mediated by different neural mechanisms, that are differentially affected by deprivation.

Adolescent↗
PubMed1999

The effects of simulated cataract on reading with normal vision and simulated central scotoma.

Reading rates are slower for persons with low vision than for normally-sighted persons. This study investigated the change in reading performance and reading eye movements when we simulated the two most common causes of low vision--central field loss and cataract--and their combination (scotoma + cataract). Three subjects read sentences with each of these simulated impairments at five different letter sizes. They required larger letters to read with the cataract or scotoma than they did with normal vision, and larger still to read with scotoma + cataract; the change in eye movements relative to normal vision was similar across conditions. When reading large letters (1.61 degrees), the cataract had almost no effect, while the scotoma and scotoma + cataract reduced reading rate for two of the subjects. The cataract had a greater impact on performance relative to normal vision for these same two subjects, while for the third subject the cataract had a greater impact with the scotoma in place. Cataract extraction tends to be postponed in patients with central field loss because it is not perceived to be beneficial. The findings from this study, as well as others, suggest that patients with central field loss would benefit from cataract extraction.

Adult↗
PubMed1988

Vision following helium ion radiotherapy of uveal melanoma: a Northern California Oncology Group study.

One hundred eighty-six uveal melanoma patients were treated with helium ion radiotherapy at Lawrence Berkeley Laboratory and followed for at least 6 months. (Follow-up times ranged from 6 to 90 months; median 26.4 months.) At last examination, 92 of 186 patients (49%) had visual acuity of 20/200 or better in the treated eye. Univariate statistical analysis revealed that post-treatment vision correlated with tumor size, distance between tumor and optic disc, distance between tumor and fovea, pretreatment visual acuity, dose delivered to the optic disc, and dose delivered to the fovea (p less than .05). Neither the maximum tumor dose nor site of tumor origin (ciliary body vs. choroid) correlated with post-treatment vision on a univariate basis. However, multivariate statistical analysis revealed that the strongest independent risk factors influencing vision outcome (p less than .05) were tumor size, pretreatment visual acuity, tumor-fovea distance, and maximum tumor dose. Neither the fovea dose nor the dose to optic disc appeared to significantly affect vision outcome when other variables were taken into account. These results suggest that post-treatment visual acuity of 20/200 or better can be achieved in one-half of uveal melanoma patients treated using helium ion irradiation. Several independent risk factors affecting vision outcome have been identified.

Helium↗
PubMed1997

Active vision therapy for pseudophakic amblyopia.

PURPOSE: To study the benefit of active vision therapy using various pleoptic methods in pseudophakic amblyopic children and young adults. SETTING: Daljit Singh Eye Hospital, Amritsar, India. METHODS: This study comprised 160 consecutive pseudophakic amblyopic patients who had had iris-claw lens implantation for congenital or traumatic cataract. Their ages ranged from 3.5 to 25.0 years. Before active vision treatment, visual acuity was worse than 20/200 in 63 patients (39.3%), 20/200 in 77 (48.1%), 20/120 to 20/80 in 14 (8.7%), and 20/60 in 6 (3.7%). The methods included Haidinger brushes on the synoptophore, after images, CAM stimulator, drawings on the cheiroscope, Pigeon-Cantonnet stereoscope, video games with the amblyopic eye, and exercises for promoting eye-hand coordination. Mean duration of therapy was 6 months. RESULTS: After therapy, visual acuity was worse than 20/200 in 31 patients (19.4%), 20/200 in 38 (23.7%), 20/120 to 20/80 in 41 (25.6%), 20/60 to 20/40 in 36 (22.5%), and 20/20 in 14 (8.7%). In 20 patients (12.5%), all younger than 15 years, visual acuity decreased within 1 month after treatment stopped. However, vision was rapidly restored after another session of active vision therapy. CONCLUSIONS: Active vision therapy helped improve visual acuity in the majority of young pseudophakic amblyopes.

Adolescent↗
PubMedDate not supplied

Sampling in spatial vision.

The human visual system is capable of making spatial discriminations with extraordinary accuracy. In normal foveal vision, relative position, width or size can be judged with an accuracy much finer than the size or spacing of even the smallest foveal cones. This remarkable accuracy of spatial vision has been termed 'hyperacuity'. Almost a century ago Ewald Hering proposed that the accuracy of Vernier acuity could be accounted for by averaging of discrete samples along the length of the lines comprising the targets; however, the discovery that Vernier acuity of a few arc seconds could be achieved with dots has rendered the nature and role of sampling in spatial discrimination unclear. We have been investigating the sampling of spatial information in central and peripheral vision (the perifovea) of normal human observers and in observers with strabismic amblyopia. Our results, presented here, show that peripheral vision and central vision of strabismic amblyopes differ qualitatively in their sampling characteristics from those of the normal fovea. Both the periphery and the central visual field of strabismic amblyopes demonstrate marked positional uncertainty which can be reduced by averaging of spatial information from discrete samples.

Amblyopia↗
PubMed2003

Ultraviolet vision in a bat.

Most mammals, with the exception of primates, have dichromatic vision and correspondingly limited colour perception. Ultraviolet vision was discovered in mammals only a decade ago, and in the few rodents and marsupials where it has been found, ultraviolet light is detected by an independent photoreceptor. Bats orient primarily by echolocation, but they also use vision. Here we show that a phyllostomid flower bat, Glossophaga soricina, is colour-blind but sensitive to ultraviolet light down to a wavelength of 310 nm. Behavioural experiments revealed a spectral-sensitivity function with maxima at 510 nm (green) and above 365 nm (ultraviolet). A test for colour vision was negative. Chromatic adaptation had the same threshold-elevating effects on ultraviolet and visible test lights, indicating that the same photoreceptor is responsible for both response peaks (ultraviolet and green). Thus, excitation of the beta-band of the visual pigment is the most likely cause of ultraviolet sensitivity. This is a mechanism for ultraviolet vision that has not previously been demonstrated in intact mammalian visual systems.

Adaptation, Physiological↗
PubMed1976

Dominance of touch by vision: generalization of the hypothesis to a tactually experienced population.

It is now held that in conditions where there is conflicting sensory information vision dominates touch. The present study was designed to place boundary conditions on the generality of the hypothesis by comparing the performance of tactually experienced subjects - potters - with university students on a form-perception task in which a square was optically distorted so as to appear rectangular. Subjects examined the square haptically and visually, and matched it by touch or vision. Although potters were more accurate than students when not permitted vision, tactual judgements of both were dominated by vision when they were presented with conflicting information. In a supplementary study longer, more active exploration and emphasis on the necessity of matching by touch had no differential effect. In a third study it was found that a range effect produced by the comparison stimuli could explain the lesser accuracy of the students when they were making haptic judgements. The generality of the hypothesis that vision dominates touch is strengthened by our failure to refute it.

Adolescent↗
PubMed1990

Visual perception and the guidance of locomotion without vision to previously seen targets.

Two experiments were performed to assess the accuracy and precision with which adults perceive absolute egocentric distances to visible targets and coordinate their actions with them when walking without vision. In experiment 1 subjects stood in a large open field and attempted to judge the midpoint of self-to-target distances of between 4 and 24 m. In experiment 2 both highly practiced and unpracticed subjects stood in the same open field, viewed the same targets, and attempted to walk to them without vision or other environmental feedback under three conditions designed to assess the effects on accuracy of time-based memory decay and of walking at an unusually rapid pace. In experiment 1 the visual judgments were quite accurate and showed no systematic constant error. The small variable errors were linearly related to target distance. In experiment 2 the briskly paced walks were accurate, showing no systematic constant error, and the small, variable errors were a linear function of target distance and averaged about 8% of the target distance. Unlike Thomson's (1983) findings, there was not an abrupt increase in variable error at around 9 m, and no significant time-based effects were observed. The results demonstrate the accuracy of people's visual perception of absolute egocentric distances out to 24 m under open field conditions. The accuracy of people's walking without vision to previously seen targets shows that efferent and proprioceptive information about locomotion is closely calibrated to visually perceived distance. Sensitivity to the correlation of optical flow with efferent/proprioceptive information while walking with vision may provide the basis for this calibration when walking without vision.

Adult↗
PubMed2000

Cross-modal interaction between vision and touch: the role of synesthetic correspondence.

At each moment, we experience a melange of information arriving at several senses, and often we focus on inputs from one modality and 'reject' inputs from another. Does input from a rejected sensory modality modulate one's ability to make decisions about information from a selected one? When the modalities are vision and hearing, the answer is "yes", suggesting that vision and hearing interact. In the present study, we asked whether similar interactions characterize vision and touch. As with vision and hearing, results obtained in a selective attention task show cross-modal interactions between vision and touch that depend on the synesthetic relationship between the stimulus combinations. These results imply that similar mechanisms may govern cross-modal interactions across sensory modalities.

Attention↗