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Biomedical subjects

F Vital-Durand

Publications and source records attributed to F Vital-Durand.

At least 19 recordsLinked to original sources
PubMed2006

New standardised texts for assessing reading performance in four European languages.

AIMS: To develop standardised texts for assessing reading speed during repeated measurements and across languages for normal subjects and low vision patients. METHODS: 10 texts were designed by linguistic experts in English, Finnish, French, and German. The texts were at the level of a sixth grade reading material (reading ages 10-12 years) and were matched for length (830 (plus or minus 2) characters) and syntactic complexity, according to the syntactic prediction locality theory of Gibson. 100 normally sighted native speaking volunteers aged 18-35 years (25 per language) read each text aloud in randomised order. The newly designed text battery was then applied to test the reading performance of 100 normally sighted native speaking volunteers aged 60-85 years (25 per language). RESULTS: Reading speed was not significantly different with at least seven texts in all four languages. The maximum reading speed difference between texts, in the same language was 6.8% (Finnish). Average reading speeds (SD) in characters per minute are, for the young observer group: English 1234 (147), Finnish 1263 (142), French 1214 (152), German 1126 (105). The group of older readers showed statistically significant lower average reading speeds: English 951 (97), Finnish 1014 (179), French 1131 (160), German 934 (117). CONCLUSION: The authors have developed a set of standardised, homogeneous, and comparable texts in four European languages (English, Finnish, French, German). These texts will be a valuable tool for measuring reading speed in international studies in the field of reading and low vision research.

Adolescent↗
PubMed2001

Variation of chromatic sensitivity across the life span.

Thresholds were measured along three directions in color space for detecting an equiluminant color change of a set of bars embedded in a larger field of spatio-temporal achromatic noise for observers ranging in age from 3 months to 86 years. Pre-verbal observers were assessed with a forced-choice preferential-looking technique while older observers responded orally or manually. Over the life span, thresholds could be described along each color axis tested by a curve with two trends. Thresholds decreased with each doubling of age by nearly a factor of two until adolescence. Thereafter, thresholds increased by a factor of 1.4-2 with each doubling of age. Sensitivity to chromatic differences varied similarly along all three axes tested, suggesting uniformity in the sensitivity of chromatic mechanisms across the life span.

Adolescent↗
PubMed1999

Development of the optokinetic system in macaque monkeys.

Optokinetic nystagmus in response to horizontal movement of a whole field random dot pattern was measured in infant macaque monkeys from the first week to about 5 months after birth using electrooculography. During monocular and binocular viewing conditions stimulus velocities were varied between 10 and 120 degrees/s. Monocular stimulation in the temporonasal direction yielded slow phase gain of the optokinetic system which was relatively constant for a given stimulus velocity over the whole period of observation. Gain during nasotemporal stimulation was also clearly present but significantly lower at early stages and increased during further development. This asymmetry of monocular horizontal optokinetic nystagmus (OKN) clearly depended on the stimulus velocity. At lower stimulus velocities (10-20 degrees/s) OKN was largely symmetrical at 2-5 weeks of age. At higher stimulus velocities (40 degrees/s) symmetry was reached at about 12 weeks of age or even much later (80-120 degrees/s).

Aging↗
PubMed1996

Tackling amblyopia in human infants.

Amblyopia can possibly be avoided if it is detected early and treated appropriately. It remains to be decided whether the general population should be screened or whether a subpopulation of infants likely to develop this pathology can be isolated. A population study using the odds ratio was performed on a group of unselected infants (n = 2143) aged 5-15 months who attended a surveillance programme. Results show that a family history of visual defect has a 'protective' effect on individual infants, most probably because more of these infants are brought in for a check-up at an early age on the parents' initiative. The risk factor with the highest predisposition for amblyopia was found to be anisometropia. These results indicate the necessity for screening of refraction and resolution defects in the whole population. The French health authorities have recently decided to provide for a visual assessment visit to all infants at the age of 9 months.

Age Factors↗
PubMed1992

Acuity card procedures and the linearity of grating resolution development during the first year of human infants.

Since the early times of preferential looking (PL), improvement of procedures to test visual resolution in infants has reached the point where the technique is spreading to clinical practice as it is applicable to a large range of age with a high degree of reliability. Acuity cards allow estimation of bi- and monocular acuity in a few minutes. Data from the literature, obtained with various PL techniques and procedures are compared to explain some incongruities. Procedures for presentation of the cards and criteria for threshold determination can greatly bias the data when they do not take into account the infant's behavioral requirements. To test the linearity of the development of visual resolution, a series of grating acuity measurements was performed on a population of 11 normal infants, regularly tested during their first year of life in optimal conditions. It was observed that: (1) grating acuity develops very regularly during the first year, (2) the two eyes never differ from each other by more than the smallest difference measurable with the equipment used (one half-octave), (3) binocular acuity appears to slightly exceed monocular acuity. These results stress the need for early detection of deviation from the norm and prompt therapeutic action.

Aging↗
PubMed1990

[Postnatal development of visual functions in primates].

The author presents the results of experimental investigations performed in apes in which he evaluated the development of the visual system. Immediately after the birth the animal's lids were stitched together, first in one eye than in the second one; at the same time the first one was opened. Electrodes were then introduced surgically to the region of the lateral geniculate bodies and to the brain cortex. The function of the visual pathways and of the visual cortex were evaluated by using differential visual stimuli. Greatest changes were seen by the author in the visual cortex. He feels that the process of formation of the visual reaction in apes is finished around the second month of life. On the basis of these investigations he discusses the mechanisms of origination of amblyopia ex anopsia in children. He encourages the earliest possible examination of the visual acuity in babies and the undertaking of treatment of amblyopia before the 1st year of life.

Animals↗
PubMed1989

[Measurement of visual acuity in infants in 6 minutes: Teller's Acuity Cards].

Most of the development of infant visual function occurs during the first year of life. Early pathological symptoms affecting visual or oculomotor processes, particularly ocular misalignment or amblyopia, should be detected and treated at the earliest age. Orthoptic and ophthalmological tests have been available for a long time but there remained a need for a convenient test for measuring visual acuity. Preferential looking techniques fulfill this demand and have been proven reliable and convenient to estimate visual acuity in preverbal infants. A new commercial presentation of the test, called Teller Acuity Cards, is described. Testing an infant was rapid, 5 to 6 minutes for a normal child, and easy because the child enjoys the convivality of the situation. Space requirement is reduced. Measures were taken from a population of 50 normal children aged 4 to 12 months. All children responded in the three situations, binocular and monocular (there was no blind eye in the group). Grating acuity values were higher than those obtained by projection preferential looking techniques. Binocular acuity was 6.5 cycles/deg (approximately 2.5/10) at 4 months of age, 9.8 cycles/deg (approximately 3.3/10) at 9 months and up to 13 cycles/deg (approximately 5/10) around 12 months. Acuities were found to be half an octave lower in monocular condition as compared to binocular. Orthoptic and ophthalmological check-up of infants is important, especially in case of children at risk of visual disorder. In most instances acuity can be preserved by therapeutic action provided it is initiated during the first year of life, when sensitivity to appropriate stimulation is at its peak.(ABSTRACT TRUNCATED AT 250 WORDS)

Humans↗
PubMed1988

[Early evaluation of the vision of infants: baby vision, a reality today].

Non invasive techniques such as preferential looking, Teller acuity cards and orthoptic examination allow an early detection and treatment of visual defect. As early as 3 months of age, the pediatrician should refer to an ophthalmologist any child at risk on the ground of its personal or family history. Visual evoked potentials and retinography should be used in the case of more severe problems.

Electronystagmography↗
PubMed1986

Organization and post-natal development of the monkey's lateral geniculate nucleus.

We have studied the properties of neurones in the lateral geniculate nucleus (l.g.n.) of Old World monkeys, both in mature animals and throughout post-natal development. Cells were classified as X (linear) or Y (non-linear) on the basis of their responses to contrast-reversing achromatic gratings ('null position test'). In older animals virtually all parvocellular neurones and the majority of magnocellular units were X cells; only about 15% of magnocellular neurones displayed highly non-linear spatial summation, with no 'null position', typical of Y cells. X cells could not reliably be distinguished from Y cells, nor magnocellular from parvocellular, on the basis of their temporal patterns of discharge. Some Y cells responded transiently to contrast reversal of a grating far from the receptive field but X cells showed little or no such 'shift effect'. The spatial resolution of mature l.g.n. cells varied with the eccentricity of their receptive fields such that the best of them, at each point in the visual field, resolved drifting achromatic gratings about as well as a human observer. X cells in parvocellular and magnocellular layers had similar 'acuities', even in the central foveal representation, but Y cells generally had poorer resolution. Receptive fields in the temporal retina tended to have lower resolution than those at comparable eccentricities in the nasal retina. Even on the day of birth all cells we studied responded to visual stimulation and virtually all could be classified as X or Y. The laminar distribution of cell types and the general morphological appearance of the nucleus seemed very similar to those in the adult, but neurones in very young animals had low spontaneous activity, sluggish responses, and latencies to visual stimulation longer than any we saw in the adult. Until 3 weeks of age or so, many neurones suffered cumulative 'fatigue' when visually stimulated over several minutes. Visual latency was essentially mature by about 10 weeks. In the l.g.n. of the neonatal monkey there was little variation in neuronal 'acuity' with eccentricity: even in the foveal area the best cells could resolve only about 5 cycles/deg. Over the first year or more of life there is a gradual increase in responsiveness and about a 7-fold improvement in spatial resolution for foveal l.g.n. cells, correlating roughly with the behavioural maturation of visual acuity.

Action Potentials↗
PubMed1986

Effects of visual deprivation on the development of the monkey's lateral geniculate nucleus.

We have studied the physiological properties of cells in the deprived layers of the lateral geniculate nucleus (l.g.n.) in monkeys monocularly deprived from birth for up to 27 weeks, and compared them with results from the non-deprived layers in the same animals and in a series of normal animals. Despite the relative shrinkage of cell bodies in the deprived layers, units were easily isolated, were visually responsive and could readily be classified as linear (X) or non-linear (Y) by means of tests of spatial summation. The laminar distribution of cell types and the proportion of Y cells did not seem to be affected by deprivation. The patterns and latencies of discharge produced by contrast-reversing gratings did not differ grossly between deprived and non-deprived cells. The peak firing frequencies for drifting gratings were also similar. The degree of surround antagonism (though very variable from cell to cell) seemed unaffected by deprivation. Most surprising of all, there was little or no deficit in the spatial resolution of the receptive fields of deprived cells. Recordings were always taken ipsilateral to the deprived eye, and neural 'acuity' tended to be sligtly lower in the deprived laminae than the non-deprived. However, this nasal/temporal asymmetry in spatial resolution was not obviously more pronounced than in normal animals. Neural 'acuity' was not abnormally low in either contralateral or ipsilateral layers in the l.g.n. of an animal binocularly deprived from birth until a year of age. We have not examined chromatic properties or temporal characteristics adequately to say whether they are affected by deprivation. Paradoxically, although the post-natal maturation of visual acuity in normal monkeys seems to be mainly limited by peripheral factors, deprivation (which causes a profound defect of behavioural acuity) does not seem to interfere substantially with physiological development of the retina or the geniculate nucleus.

Action Potentials↗
PubMed1985

[3 parallel channels transmit visual information from the retina. Anatomic and physiologic arguments].

Two hypotheses applied to the information processing of visual messages from the primate retina toward cortical areas are tested against experimental data. The hierarchical theory is weakened by the existence of independent anatomical and physiological parallel channels from ganglion cells to the visual cortex, devoted to specific parameters of the message. X linear and Y nonlinear cells are classified according to the presence or absence of a linear summation process integrating the elementary responses from the subfields which constitute the receptive field. Other response properties might be more loosely correlated with response linearity: X cell responses are sustained, have a long latency and are sensitive to color contrasts. All cells in parvocellular layers of the Lateral Geniculate Body are X, and more than half the magnocellular layers as well. Y cells have brief, transient and short latency responses, very sensitive to monochromatic contrast and are exclusively found in magnocellular layers. Visual information is processed toward the cortex through anatomically and physiologically defined channels specialized in the transmission of different parameters of the visual stimulation.

Animals↗
PubMed1985

[The preferential looking technic: material and procedure for testing baby vision].

The preferential looking technique, together with a cover test, retinoscopy and a fundus examination is done in a hospital setting for screening and follow-up of visual deficiencies in infants between 3 and 12 months of age. A series of granting from .375 to 18 cycles per degree are generated by slides, paired with a matched mean luminance uniform area. The child's preferred gaze orientation is determined by an orthoptist unaware of the randomized side of the granting, from a picture of the infant displayed on a closed-circuit television. The baby is gratified after each positive trial. The finest grating toward which the baby systematically orients its gaze is a behavioral estimate of its spatial resolution ability. Binocular and monocular testing are performed in at least 15 minutes. Details of equipment and procedure are described.

Differential Threshold↗