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PubMed2004

Optotype and grating visual acuity in patients with ocular and cerebral visual impairment.

PURPOSE: To investigate the discrepancy between grating and optotype visual acuity in children with visual impairment due to brain and/or ocular abnormalities. METHODS: Better eye acuity at 114 cm was studied in 81 patients (ages, 5-24 years) attending special schools for the visually handicapped. Fourteen patients had a brain abnormality, 48 had an ocular disorder, and 19 had both. Three acuity tasks were administered: detecting gratings in one of two positions, discriminating the orientation of single gratings, and discriminating the orientation of uncrowded Landolt-C optotypes. The three paradigms were similar in stimulus contrast, luminance, presentation mode, and psychophysical procedure. RESULTS: Overall, grating acuity was better than optotype acuity, and the disparity increased with poorer optotype acuity. The largest discrepancies occurred in patients with brain abnormality, but disparities were also large in patients with optic nerve disorder. In patients with ocular and brain abnormality, grating acuities were only mildly better and not different from patients with only ocular abnormality. Grating orientation and grating detection tasks yielded similar thresholds, except in patients with cerebral visual impairment and with optic nerve disorder, whose grating detection acuity was better than grating orientation acuity. CONCLUSIONS: Grating-to-optotype acuity superiority is typically large in visual disorders involving the brain. The closely matched test paradigms point to stimulus characteristics as the explanation. However, because the discrepancy decreased with grating orientation acuity instead of grating detection acuity, the complexity of the response required also plays a role.

Adolescent↗

PubMed1983

Visual exploratory activity of hemiplegic patients viewing the motor-free visual perception test.

Eye movements of adult hemiplegics (11 right- and 9 left-brain-damaged patients) and 11 nonimpaired controls were recorded as they viewed selected cards of the Motor-free Visual Perception Test. The major finding was that neither group of patients exhibited an asymmetry of visual exploration (unilateral visual neglect) as they viewed the cards. Their scanning strategies were, however, unsystematic and irregular. In addition, both groups of patients scanned the cards longer and made more errors than controls. Use of the Motor-free Visual Perception Test as an appropriate measure for the general assessment of visual-perceptual processing abilities of adult brain-damaged patients who lack severe clinical manifestations of neglect is discussed.

Brain Damage, Chronic↗

PubMed2005

Incidental visual memory for targets and distractors in visual search.

We explored incidental retention of visual details of encountered objects during search. Participants searched for conjunction targets in 32 arrays of 12 pictures of real-world objects and then performed a token discrimination task that examined their memory for visual details of the targets and distractors from the search task. The results indicate that even though participants had not been instructed to memorize the objects, the visual details of search targets and distractor objects related to the targets were retained after the search. Distractor objects unrelated to the search target were remembered more poorly. Eye-movement measures indicated that the objects that were remembered were looked at more frequently during search than those that were not remembered. These results provide support that detailed visual information is included incidentally in the visual representation of an object after the object is no longer in view.

Attention↗

PubMed2005

Intermittent visual information and the multiple time scales of visual motor control of continuous isometric force production.

In an experiment, we examined the effect of intermittency (from 25.6 Hz to 0.2 Hz) of visual information on continuous isometric force production as a function of force level (5%, 10%, 25%, and 50% of maximal voluntary contraction [MVC]). The amount of force variability decreased and the irregularity of force output increased as a function of increased visual intermittency rate. Vision was found to have an influence on the frequency structure of force output up to 12 Hz, and the 25% MVC force level had more high-frequency modulations with higher rates of visual information. The effective use of intermittent visual information is mediated nonlinearly by force level, and there are multiple time scales of visual control (range, approximately 0 - 12 Hz) that are postulated to be a function of both feedback and feedforward control processes.

Exercise↗

PubMed1975

[Effect of visual deafferentiation on the ultrastructure of synapses of the rat visual cortex].

Electron microscopic study and quantitative analysis of the visual cortex synapses in 14, 30 and 60-day-old rats were performed after bilateral enucleation of newly-forn rats. A great amount of synapses of other functional systems was shown to be functioning in the area striata in addition to the synapses formed by specific visual afferents. Alterations in the synapses of the area striata of blind rats are developing gradually, achieving the greatest pronouncement in 60-day-old rats. These changes develop according to the type of atrophic process in connection with dysfunction. The atrophic alterations of the synapses were found both in axo-somatic and axo-dendritic synapses on the dendrite trunks and on the thorns. The alterations of synapses being concentrated in layer IV. The quantitative ratio of different kinds of atrophied synapses in the cross-section of the visual cortex was different suggesting the following conclusion about the distribution of the visual afferents. In layers I and III the visual afferents formed mostly axon-thorn contacts and less amount of axo-somatic and axo-dendritic synapses on the dendrite trunks. In layer IV they mainly formed axo-somatic and axo-thorn synapses and less amount of axo-dendritic ones on the dendrite trunks. In layers V and VI they mainly contact with the dendrite trunks and with the nervous cell bodies and more rarely with thorns.

Afferent Pathways↗

PubMed1975

Effect of preconditioning visual stimulus duration on visual-evoked responses to a subsequent test flash in Down's syndrome and nonretarded individuals.

Visual-evoked responses to a visual test flash preceded by three different durations of a visual conditioning flash having the same intensity and form were recorded from 8 Down's syndrome subjects and 9 nonretarded CA-matched control subjects. Both groups showed a significant decrease in visual-evoked response perimeters to the test flash as the duration of the visual conditioning flash increased from 1 to 100 msec. For the 1000-msec condition, perimeters of Down's syndrome subjects showed a significant increase, and this was significantly greater than the nonretarded group. These results suggest that Down's syndrome individuals have deficits in their neural processing of sensory information.?23Author

Adolescent↗

PubMed2003

[Calculating the mean visual acuity and the change in visual acuity with a decimal acuity chart].

The decimal visual acuity chart is not easy to use for statistical analysis and requires a transformation into LogMAR units (decimal logarithm of the Minimum Angle Resolution). In contrast to the decimal chart, the logarithmic chart has an arithmetic progression and a constant interval between lines. The LogMAR chart makes statistical analysis of visual acuity easy. Change in visual acuity is calculated directly by subtracting LogMAR data, while the average visual acuity is obtained with the arithmetic mean value of the LogMAR data. The mean acuity expressed in LogMAR units can be transformed into a decimal chart for a more comprehensive result. To calculate the average visual acuity directly from the decimal data, the geometric mean value must be used instead of the arithmetic mean value.

Calibration↗

PubMedDate not supplied

[Visual motor and visual defects in spina bifida].

Among the numerous problems that spina bifida (SB) patients are faced with, impairments to the visual apparatus are often considered late and are not covered extensively in the literature. At the Pediatric Department of the University of Padua, an assessment of the visual function of 59 SB patients between 5 months and 26 years of age (29 male and 30 female) has been carried out by means of an ophthalmologic protocol. As far as the alteration of the exstrinsic ocular mobility is concerned, 44% (26/59) of our patients revealed a manifest squint and only 3% (two patients) suffered from a latent squint. The most frequent type is a convergent squint (80%). The assessment of visual acuity made through Optotype was good in 82% of the cases (unlike what is commonly reported in the literature) and mild in 18%. None of the patients manifested hypovision. Refraction defects were present in 59% (34/59) of the patients. Regular ophthalmologic evaluations from birth or from diagnosis allow ophthalmologic treatments that are tailored to children suffering from SB and also enable them to reach and maintain a good visual standard and to observe the subtle symptoms of endocranial hypertension sooner. An early discovery and correct treatment of visual problems improves cognitive and motive performance as well as the autonomy of SB patients.

Child↗

PubMed1991

The significance of testing preoperative visual function in cataract using laser interferometric visual acuity and ERG.

Tests of preoperative visual function and prediction of postoperative E chart visual acuity (ECVA) using laser interferometric visual acuity (LIVA) and electroretinogram (ERG) were performed in 16 cases (19 eyes) of cataract. The results showed that the coincident rate between preoperative LIVA and postoperative ECVA was 63.2%, and there was a parallel correlation between preoperative amplitude of photopic ERG b-wave and postoperative ECVA in 79.0% of the eyes. Comparing these two methods, the test of LIVA is very simple, fast, and is easily accepted by the patients with cataract. ERG is an objective method, which is slightly influenced by dense lens, but the test is more complex. Therefore, the combined use of these two methods will provide a more comprehensive and correct evaluation of preoperative visual function and a more reliable prediction for postoperative visual acuity in patients with cataract.

Adolescent↗

PubMed1990

[Value of a study of contrast sensitivity in the evaluation of visual function: applications to pathology and visual selection].

Spatial contrast sensitivity function appears to give the most general description available for the basic aspect of spatial visual performance. Classical measurement of visual acuity is unable to give us a fine appreciation of visual function. Visual acuity is only one aspect of the complex process of sight. We have tested contrast sensitivity to detect silent lesions of the visual pathway. In multiple sclerosis we have demonstrated a bilateral involvement in almost all cases. In primary open angle glaucoma contrast sensitivity is affected before perimetry data are able to show any defect. We have the same results in early stages of diabetic retinopathy. Contrast sensitivity testing shows great promise for detection of eye defect in drivers and industry workmen.

Contrast Sensitivity↗

PubMed1989

[Objective assessment of senile changes in visual function by visually evoked cortical potentials].

The P100 peak latency of pattern visually evoked cortical potentials (P-VECP) was found to increase and amplitude decrease in the elderly depending on stimulus conditions. Using either of these as a criterion, changes of visual function with aging were quantitatively assessed both in humans and animals. Contrast threshold was found to increase at higher spatial frequency ranges and the luminance threshold increased more than 0.8 log unit. Also, the contrast threshold increased due to a smaller pupillary area and there was progressive decrease of the temporal frequency curves with age for lower frequency ranges of less than 10 rev/sec. In addition, a sensitivity decrease for the upper visual field was detected plus blue-yellow defects and a decrease in the amplitude of accommodation. In order to exclude the effect of senile changes of the crystalline lens, the luminance threshold, the accommodation power and color sense were investigated in pseudo-phakic eyes with a posterior chamber lens. No significant differences were found between phakic and pseudo-phakic eyes. Accordingly, it was suggested that reduced transparency and yellowish changes of the crystalline lens do not essentially contribute to the loss of function in the elderly found in the present study, but the neuronal pathway was responsible. As a clinical model of senescence, cases of juvenile parkinsonism were investigated, during L-dopa treatment and after ceasing it. The deficiency of the neural-transmitter of the higher visual pathway was indicated in the elderly, also. Animal experiments on neuronal dysfunction in rats and mice suggested no aging effects in ERGs, whereas VECP peak latency for higher temporal frequencies increased with age. The assumption that the elderly changes occur at the neuronal level was supported by a loss of optic nerve fibers in mice with age. The numbers of optic nerve fibers measured were 48,115, 50,875 in the 3-month-old and 6-month-old groups, respectively, and decreased to 43,175 in the 30-month-old group. Though our results indicated the senescence of visual function at the neuronal level, it was not as much as shown by other sensory organs. It was therefore presumed that there might be a certain feed-back system from the brain to the retina.

Adolescent↗

PubMed1989

Quantitative visual psychophysics during the period of European enlightenment. The studies of the astronomer and mathematician Tobias Mayer (1723-1762) on visual acuity and colour perception.

During the sixth decade of the 18th century, Tobias Mayer, Professor of Astronomy and Applied Mathematics (Economy) at the University of Göttingen, performed two investigations on quantitative visual psychophysics. He deduced a power law for the dependence of visual acuity on the intensity of light by which the stimulus pattern was illuminated. In his measurements he compared visual acuity determined with single black dots and visual acuity measured with gratings or checkerboard patterns; the latter he considered as the "real" measurement of visual acuity. Mayer also developed a three-dimensional hexaedric colour space from the definition of subtractive colour mixtures of three primary pigments (red, yellow, blue). This colour space can be considered as the predecessor of the later colour tables of Ostwald and Munsell. Mayer gave a simple quantitative description of each of the 819 hues in his colour space. Both psychophysical studies developed out of Mayer's interest in practical problems in astronomy and cartography. Mayer's main scientific merits were in the field of astronomy and mathematical geography. His psychophysical studies were performed in the spirit of enlightenment with the a priori assumption that the performance of the human perceptual machinery can be measured quantitatively and that the results are adequately expressed by mathematical rules. Mayer's achievements in the fields of mathematics, physics, astronomy and cartography were recently summarized by the extensive historical research of G.F. Forbes. In the present report a short biographical note precedes the description of Mayer's psychophysical studies.

Astronomy↗

PubMedDate not supplied

[Correlation of the visual and spatially oriented behaviors of white rats following the elaboration of a visual differentiation habit].

Correlation of spatial-motor and visually oriented reactions of white rats was studied by the method of three-side choice. It is shown that after acquisition of the habit of visual differentiation the visual orientation dominates only at taking feeding decision of passing to the passage. The choice of the direction of running to blinds and the choice of place of entering the passage do not depend on present visual signals location and do not reflect the state of visual differentiation habit, but are controlled by spatial memory.

Animals↗

PubMed1985

Maturation of visual callosal connections in visually deprived kittens: a challenging critical period.

The number of callosally projecting neurons (callosal neurons) which can be labeled in cortical areas 17 and 18 by horseradish peroxidase (HRP), injected in the contralateral visual cortex, is reduced to about 50% of normal in cats reared with their eyelids bilaterally sutured. In the same animals the density of HRP anterogradely transported to areas 17 and 18 is also decreased. The apparent loss of callosal neurons is limited to layers III and IV (subzone a), whereas layer VI (subzone c) is unaffected. The effect is obtained after 3 months or more but not after 1 month of deprivation. Two months of visual experience following deprivation do not restitute a normal number of callosal neurons. However, 10 days of normal visual experience preceding the deprivation are sufficient to prevent the effects of the latter. Animals deprived of vision after a short period of normal visual experience and animals allowed normal vision after 1 month of visual deprivation have a more widespread distribution of callosal neurons than do normal animals; in this way they are similar to previously described cats reared with convergent or divergent strabismus, monocular enucleation, or monocular eyelid suture. The results suggest that: vision is actively responsible for both the maintenance and the elimination of fractions of the juvenile callosal connections; the elimination which normally takes place during the second postnatal month requires normal binocular vision; and activity-dependent competition between callosal and other axons can explain the role of vision.

Animals↗

PubMed1982

Restitution of visual field in patients with damage to the geniculostriate visual pathway.

Previous experiments have investigated the effect of specific practice on partially blinded monkeys after striate cortex lesions. Similar procedures were adapted for patients suffering homonymous field defects due to geniculostriate damage. Both methods, light detection and saccadic localization, led to an enlargement of the visual field. The amount of this enlargement depended on the eccentricity of the field border as well as on the level of light sensitivity in the region between the intact field and the scotoma. Recovery of visual field included the reappearance of various visual functions (e.g. visual acuity, color identification). In periods without training visual field did not recover. It is hypothesized that recovery can take place at the level of the striate cortex, and is mediated by structures interacting with the striate cortex, e.g. the superior colliculus.

Adult↗

PubMed1993

[Visual perseveration and palinopsia: a visual memory disorder?].

Visual perseveration and palinopsia are defined as the persistence or the reappearance of the visual image. These infrequent symptoms are thought to be linked to the right hemisphere posterior areas. We report a case of this syndrome in which the initial fixation was foveal. The palinoptic image was sometimes moving. This suggests that palinopsia is due to a dysfunction of the visual memory, rather than of the visual system: this dysfunction may be related to hyperactivity of the visual buffer.

Brain Neoplasms↗

PubMed1994

Visual readaptation after flash exposure under scotopic conditions. A study using optokinetic nystagmus as an indicator of visual perception.

The purpose of the present study was to establish a method for objective measurements of visual readaptation after flash exposures and to define a model for measurements. Influences of target direction, luminance and velocity on optokinetic nystagmus (OKN) were investigated under scotopic conditions. Visual readaptation was measured using OKN as an indicator of visual perception after exposure to a flash. The interval between the triggering of the flash and the reoccurrence of OKN was defined as the visual readaptation time (RAT). A Goldmann perimeter hemisphere was used for flash stimulation. A horizontally moving vertical grating projected inside the hemisphere was used as the OKN stimulus. Eye movements were recorded by DC electrooculography (EOG). The dependence of RAT on the dose of the flash, the wavelength of the flash and the luminance of the OKN target were investigated. The precision of the measurement method was studied. This includes the analysis of the variance due to the experimental occasions, the repeated exposures, the sexes of the subjects, the methods for recognition of OKN and the ways of visual adaptation before measurements. The contributions of retinal receptor and the neural activity to RAT were investigated by electroretinography (ERG). The influences of target direction and luminance on binocular motion perception and OKN as well as monocular OKN were examined at various target velocities. The dependence of the frequency and amplitude of eye jerks during monocular OKN on target luminance and velocity were also examined. It was found that RAT increases with increasing doses of the flash or decreasing luminance of the grating. RAT is most extended after flashes near 520 nm. RAT does not differ between experimental occasions, between a manual and a semi-automatic method for recognition of OKN, between the sexes and between goggle adaptation and ordinary dark adaptation. There is a reduction of RAT due to repeated flash exposures. The data collected indicate that a well-defined model is crucial for measurements of RAT. The measurement of ERG showed that RAT is mediated by both retinal receptor and the neural activities. The receptor component depends on the wavelength of the flash while the neural component is wavelength-independent. Moreover, it was found that motion perception and OKN gain does not differ between right and left target directions. For a given target velocity, motion perception and OKN gain under both binocular and monocular viewing conditions increase with increasing luminance of the target with an exponential decay. The maximum OKN gain decreases as target velocity increases.(ABSTRACT TRUNCATED AT 400 WORDS)

Adaptation, Ocular↗

PubMed1996

[Delayed visual maturation--a differential diagnostic challenge. A follow-up study of 13 children with delayed visual development with or without other developmental disorders].

Early visual impairment represents several diagnostic possibilities from specific delayed visual maturation (type 1) with an excellent prognosis to more complex conditions with other ocular or neurological signs (type 2-4). Visual attention and interaction has been an interesting field of study in the interaction between biologically pre-programmed neonatal competencies and social facilitation. From these studies we can probably learn more about ((cloudy)) diagnoses such as cortical visual impairment, attention deficit hyperactivity disorder and autism. Investigations and follow-up of 13 infants who did not show any visual interest at 6 - 12 weeks old are presented, along with proposals for the clinical management of these problems.

Developmental Disabilities↗