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Using a new apparatus which enables us to measure in a continual manner the visual acuity for any distance; we have found considerable changes in the acuity between 24 metres and 10 centimetres. A drop in the visual acuity was found at the near vision. From dioptric and non-dioptric factors, we have infered our interpretation, which touches the question of visual fatigue and near vision.
One of the most common principles of cortical organization is that neurons with similar response properties are clustered together in space. Thereby the environment is represented in an orderly fashion on the cortical surface in a so-called "cortical map". In primary visual cortex, for instance, neurons with similar orientation preferences are grouped together, forming the orientation preference map. Optical imaging of intrinsic signals allows to investigate the organization of such maps in vivo. Neuronal activity was measured utilizing the fact that the transition from oxy-hemoglobin to hemoglobin in active brain areas can be detected optically by recording changes in light reflectance with a high resolution CCD-camera. When using this technique to look at the exact patterning of orientation preference maps in cat visual cortex a novel principle for the organization of cortical maps was observed: orientation was not organized in parallel bands as had previously been thought but iso-orientation domains were organized radially; orientations from 0 to 180 degrees were laid out in a pinwheel-like fashion around singularities which we termed "orientation-centers". After observing pinwheel patterns in orientation preference maps in adult cat visual cortex it was also investigated how these meticulously arranged maps develop in the cortex of young kittens. Performing chronical recordings in kittens from the age of postnatal day 17 on we were able to observe how orientation maps form already during the third week of life and--under normal conditions--remain largely unchanged thereafter.(ABSTRACT TRUNCATED AT 250 WORDS)
Optic neuropathy is reported to occur in 10-30% of patients, while retinopathy is characteristic of type III OPCA. The use of visual and visual electrophysiological tests in early diagnosis and classification is promising. The relationship between visual impairment and other manifestations of these diseases has not been explored.
The distribution of Fos-like protein, suggested to be a sensitive marker for neuronal activity, was studied in the visual cortex of 60 days old rats which were either blind congenitally and had their eyelids remained closed, or were born normally in terms of their visual apparatus but were dark reared, or were dark reared and exposed to light shortly before sacrifice, or were normal and reared in normal ambient light. Regardless of the primary cause, light deprivation produced a striking increase in Fos immunoreactivity, mainly in visual areas 17 and 18 a, with Fos-positive cells predominantly located in laminae IV and VI. Exposure of dark reared rats to ambient light further enhanced Fos immunoreactivity but it did not change the distribution pattern of Fos-immunoreactive neurons.
In 5 experiments, 4-month-old infants were tested for their ability to recognize degraded visual targets as a function of individual differences in fixation duration. Targets were degraded by removing 10% of the total contour either from vertices (vertex-absent) or from midsegments (vertex-present). Both qualitative and quantitative differences were found in long and short lookers' ability to recognize the degraded forms. Short-looking infants were able to recognize degraded forms in both vertex-absent and vertex-present conditions, but the vertex-absent discrimination was more difficult. Long-looking infants required longer familiarization times before showing evidence of recognition in the vertex-present condition, and were unable to recognize targets in which contour was removed at vertices. The findings are discussed within the framework of the persistence of early visual processing strategies, and reliance of long-looking infants on particular local elements in visual analysis.
It is believed that long-term changes in neuronal function are orchestrated by transcription factors, such as AP-1 and ZIF 268, which are in turn regulated by synaptic stimulation. To further our understanding of the functional effects of such expression, we have examined the DNA-binding activities of both AP-1 and ZIF 268 by way of electrophoretic mobility shift assays (EMSA) on nuclear extracts from visual cortices of rats treated with selective light exposure. Visual stimulation after dark rearing increased the DNA-binding activities of both AP-1 and ZIF 268 to their highest levels within 2 hr. ZIF 268 thereafter dropped to levels similar to that observed in naive animals, whereas AP-1 DNA-binding activity continued to remain elevated even after 24 hr of stimulation. The components of the AP-1 complex, when assessed by EMSA-supershift analysis, showed considerable variability under different conditions of exposure. FosB and JunD were the major constituents of AP-1 in both naive and dark-reared animals. Brief visual stimulation (2 hr) added c-Fos, c-Jun, and JunB to this complex, whereas prolonged stimulation (6-24 hr) reduced c-Fos and c-Jun levels significantly, leaving only FosB, JunB, and JunD as the major components of AP-1. These results suggest that transcriptional control by AP-1 may be generated by selective combinatorial interactions of different members of the Fos and Jun families and that are guided by activity-dependent processes.
BACKGROUND: Henry Armaignac, a French ophthalmologist in the early twentieth century, criticized the Monoyer optometric scale, which was used to measure visual acuity. METHODS: This article discusses the "optometric scale" for visual acuity letter sizes proposed by Armaignac in a 1906 publication. CONCLUSION: Armaignac pointed out the flaws of the Monoyer visual acuity chart commonly used in France at the time and suggested an improvement in the progression of letter sizes on the chart.
This study examined the extent to which the responses of single cells in the striate cortex (V1) and the extrastriate cortex (V4) of the alert rhesus monkey are modulated by visual stimuli whose relevance in a behavioral task is varied. The animal had to detect the repetition of a visual pattern (i.e. detect similarity), preceded by a randomized number of alternations between two different patterns. The responses produced by the last, reward contingent stimulus were compared with responses obtained to that same stimulus earlier in the sequence. Modulatory effects in V1 were moderate: 31% of the cells (63 of 200) showed response increments of 20% or more to the last, reward contingent stimulus. In V4 the effects were much more pronounced: 72% of the cells (110 of 154) showed modulatory effects of more than 20%. In V4 but not in V1 orientation tuning curves showed a significant narrowing as well as a peak response increment to the behaviorally salient stimulus, suggesting a feature specific mechanism associated with the detection of similarity. Although a response decrement was observed in many cells during the repeated alternations, this effect was significantly smaller than the modulation produced by the detection of similarity. Controls included the presentation of novel stimuli during the presentation sequence which did not produce an enhanced response. It is hypothesized that the feature specific effects reported here are produced by higher order feedback systems.
When applied over the occipital pole, transcranial magnetic stimulation (TMS) disrupts visual perception and induces phosphenes. Both the underlying mechanisms and the brain structures involved are still unclear. The first part of the study characterizes the suppressive effect of TMS by psychophysical methods. Luminance increment thresholds for orientation discrimination were determined in four subjects using an adaptive staircase procedure. Coil position was controlled with a stereotactic positioning device. Threshold values were modulated by TMS, reaching a maximum effect at a stimulus onset asynchrony (SOA) of approx. 100 ms after visual target presentation. Stronger TMS pulses increased the maximum threshold while decreasing the SOA producing the maximum effect. Slopes of the psychometric function were flattened with TMS masking by a factor of 2, compared to control experiments in the absence of TMS. No change in steepness was observed in experiments using a light flash as the mask instead of TMS. Together with the finding that at higher TMS intensities, threshold elevation occurs even with shorter SOAs, this suggests lasting inhibitory processes as masking mechanisms, contradicting the assumption that the phosphene as excitatory equivalent causes masking. In the companion contribution to this one we present perimetric measurements and phosphene forms as a function of the stimulation site in the brain and discuss the putative generator structures.
The slow-wave response recorded from electrodes within the visual cortex of the awake cat has been shown to reflect the pattern processing activities of the visual cortex. In a cat deprived of pattern vision by monocular lid closure, the response evoked from the non-deprived eye by patterned and diffuse stimuli show differences similar to those found in a normal cat. However, when these same stimuli are presented to the deprived eye, the differences are not present. These slow-wave data confirm previous data from single unit recordings in showing that pattern processing is altered by deprivation.
The decrease of visual performance from the fovea towards the periphery depends upon the task tested. The slope of the decrease is generally steeper for hyperacuity than for spatial resolution and is steeper in the nasal than in the temporal hemifield. The naso-temporal asymmetry in the periphery of the visual field, beyond 20 deg eccentricity, is much more pronounced for hyperacuity than for spatial resolution. The psychophysical results show a close correlation to the cortical organization as revealed by autoradiography.
Single cells were recorded in the vestibular nucleus of normal and monocularly deprived cats and stimulated by slowly drifting large area visual patterns. We found no difference in response strength, direction specificity and binocular influence between the neurons recorded in normal and in monocularly deprived cats. This makes it very unlikely that the nucleus of the optic tract (NOT) in the pretectum provides a strong direct input to the vestibular nuclei to modulate their activity with visual stimulation.
The effects of the visual pathways and acuity dominance on visual half-field (VHF) recall of verbal stimuli were investigated with 36 right-handed male undergraduates, with the use of the Hines-Satz short-term memory paradigm under monocular conditions. Scores for stimuli transmitted via the left temporal and right nasal pathways were significantly greater than those for stimuli transmitted via the left nasal and right temporal pathways. No other significant differences were found for either the pathways or acuity dominance variables. The results were hypothesized to reflect the primary influence of hemispheric asymmetry of function on the VHF recall task.
The accuracy of a variety of finger and color confrontation tests in identifying chiasmal and optic nerve visual field defects was assessed in patients whose field defects had been established beforehand by a conventional achromatic kinetic technique on the Goldmann perimeter. Kinetic and static finger confrontation methods identified an average of 42% of the 28 chiasmal hemianopic defects. False negatives included eyes with hemianopias complete to the largest (V4e) Goldmann isopter. False positives (average, 15%) occurred in eyes containing nerve fiber bundle defects with borders that fell near the vertical fixational meridian. Kinetic and static color confrontation techniques were 78.6% sensitive to hemianopias. Accuracy did not differ significantly whether the red target was presented kinetically or statically against the tangent screen, projected on the Autoplot screen, or held in the examiner's hand without attention to background. False positives (average, 23%) were slightly greater than with finger confrontation methods and occurred not only in eyes with nerve fiber bundle defects but also in eyes with no defects in reference visual fields. Finger confrontation identified 11% or fewer of optic nerve field defects, while some color techniques detected as many as 31 1/3%. There were no false positives.
Because the pattern-reversal visual evoked response (PVER) reflects the central retinal function, PVER results generally agree with those of psychophysical tests. The visual acuities (VAs) calculated from PVER recordings and Snellen acuity (SA) measurements were compared in 500 eyes (261 patients; ages 8 to 88 years; mean, 44.5 years). The best-corrected VA was measured using the ETDRS chart, and the PVER acuity was determined by the smallest check size that produced a definite PVER (critical check size). In 288 eyes with a critical check size of 10 min of arc, the SAs ranged from 20/15 to 20/800 (mean 20/38). In 68 eyes with a critical check size of 20 min, the SAs ranged from 20/15 to 20/800 (mean 20/97). In 70 eyes with a critical check size of 40 min, the SAs ranged from 20/20 to 20/1600 (mean 20/156). In 29 eyes with a critical check size of 80 min and 14 eyes with a critical check size of 160 min, the SAs ranged from 20/50 to 20/1600 (mean 20/312 and 20/398, respectively). In 31 eyes in which the PVER was non-recordable, the SAs ranged from 20/70 to 20/3200 (mean 20/1177). The PVER acuity using the smallest check size seemed to agree with the SA, but large deviations were observed in certain subjects.
A 35 month old child was referred for electrophysiology testing with pendular nystagmus, corresponding head oscillations and reduced vision. Flash visual evoked potential (VEP) revealed large responses at the right occiput (but not the left occiput) from the right eye and similar large responses at only the left occiput from the left eye, indicating absent/deficient crossover at the chiasm. A magnetic resonance imaging (MRI) scan subsequently confirmed absence of the optic chiasm. There was no other evidence of midline brain defects. Her subsequent development to age 11 has been followed. The nystagmus has remained mainly horizontal but a torsional component was noted from age 5 years and described as see-saw at age 6 years. A small right esotropia was noted at 6 years and spectacles prescribed for low hypermetropic refractive error. Bilateral superior rectus recessions at age 7 years produced an improved head posture. Her visual acuity has remained stable at around 6/24 from age 4 years. No binocularity nor stereopsis has been demonstrated over subsequent visits.
We analyzed the long-term functional results in 102 eyes of 59 patients with childhood glaucoma with specific reference to the pattern of optic nerve damage. Optic disk photography and quantitative perimetry were used to judge the degree of damage that had been sustained. There was a predilection for initial visual field damage in the arcuate area, followed by further arcuate and nasal field loss, similar to the pattern of visual field loss seen in adult glaucoma. In children, as in adults, neural tissue appeared to be lost preferentially at the vertical disk poles. The selective pattern of glaucomatous optic nerve damage seemed not to depend upon the age of the optic nerve structures. In contrast to adult eyes, the scleral canal in children apparently enlarges with high IOP. Thus, disk cup size increase in children could occur from neural tissue loss, from scleral canal enlargement, or from a combination of the two processes.
Electrophysiological investigations restricted to the caudomedial part of the optic tectum show that the caudalmost part of the frog's visual field appears preferentially analyzed by class-2 and class-3 retinal ganglion cells and integrated by monocular T5 neurons even though this spatial region is seen by the two eyes and doubly represented on each tectum. This apparent preponderance for three types of contralateral visual units is discussed on the basis of the animal's behaviour.