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At least 1,081 records · Page 60Linked to original sources
PubMed2001

Graft location affects functional rescue following RPE cell transplantation in the RCS rat.

Photoreceptor (PRC) rescue in the dystrophic Royal College of Surgeons (RCS) rat has been well documented following a variety of interventions. Although the dystrophic process is asymmetric with respect to the horizontal meridian, little attention has been paid to the effect of topographic position on treatment outcome. In this study, RPE cells from adult congenic nondystrophic animals were injected into the subretinal space of 1-month-old dystrophic RCS rats in either the dorsal or the ventral equatorial region. Animals were followed longitudinally during the degenerative process using the pupillary light reflex (PLR). The parameter of the PLR most sensitive to PRC rescue is latency at low light levels. At 3 months of age this parameter showed statistically better performance (ANOVA, P = 0.016) for eyes with grafts placed dorsally compared to those placed ventrally or untreated controls. There was no treatment effect on amplitude. By 6 months of age the dorsal/ventral disparity in latency was less apparent and amplitude remained equivalent across groups. Late analysis of retinal whole-mounts using RT-97 fluorescent labeling showed extensive irregularities in ventral axonal morphology in all treatment groups. These results indicate that functional rescue of the RCS retina is significantly influenced by the local degenerative timetable. The role of initial local conditions on treatment outcome is worthy of consideration in other models of neuroprotection.

Analysis of Variance↗
PubMed1995

Retinotopic maps in human prestriate visual cortex: the demarcation of areas V2 and V3.

We have used PET (positron emission tomography) to chart the mapping of the retina in human occipital visual cortex and hence to locate the secondary and tertiary visual areas, V2 and V3. A group of four non-selected male volunteers was presented with dynamic stimuli that were aligned with either the vertical or the right horizontal meridians (VM or HM) from 0 degree to 29 degrees eccentricity; the vertical stimuli were restricted to either the inferior or the superior hemifields. PET scans were performed using intravenous infusion of H215O and a Siemens-CTI 953B PET scanner with 3D data acquisition. Subjects received 18 scans, divided equally among the right HM, the superior VM, and the inferior VM. Data were analyzed with SPM software. The group average result confirmed our experimental hypothesis that human occipital visual cortex has retinotopic maps similar to those of the macaque monkey. Thus human areas V2 and V3 can be defined on the basis that the border between them is formed by the HM and that the outer border of V3 is demarcated by a second representation of the VM that runs approximately parallel to the primary representation of the VM at the V1/V2 border. Furthermore, as in many mammals, the extrastriate representation of the HM is "split", such that the superior contralateral quadrant is mapped in lower V2 and V3, occupying the ventral surface of human cortex, and the inferior contralateral quadrant is mapped in upper V2 and V3, which extend over the lateral and medial surfaces of each hemisphere. After stereotaxic normalization, the position of V3 defined by retinal topography was found to correspond to that surmised from our previous PET studies employing moving stimuli.

Adult↗
PubMed2001

Functional specificity of superior parietal mediation of spatial shifting.

Using event-related functional magnetic resonance imaging (fMRI) we determined how brain activity changes when an attended target shifts its location. In the main experiment, a white square could appear at 10 possible eccentricities along the horizontal meridian. It remained on the screen for a variable period of time and then changed location. At any time the stimulus could dim briefly. Subjects had to press a button when the stimulus dimmed. In order to perform this task attention had to be locked onto the target and shift with it. Half of the runs were performed overtly and half covertly. The event of interest consisted of the shift in the location of the attentional target. The state of maintained attention occurring in between the shifts constituted the baseline. The superior parietal gyrus was activated bilaterally in response to attentional shifts. No other area showed a significant response to shifting. On the left side the amplitude of the superior parietal response correlated positively with the distance of the shift. On the right side a significant correlation was present only for overt shifts. In a separate experiment we compared the maintaining of attention at a single spatial location to passive fixation: the frontal eye fields, anterior cingulate, right dorsolateral prefrontal cortex, and inferior parietal lobule were significantly activated, indicating that the absence of a shift-related response in these areas in the main experiment was due to the fact that they were equally activated by maintaining and shifting attention. The response to spatial shifts and the correlation with the distance between the original and the new location points to a specific role of the superior parietal gyrus in shifting the locus of spatial attention.

Adult↗
PubMed1998

Comparative toxicity of eugenol and its quinone methide metabolite in cultured liver cells using kinetic fluorescence bioassays.

Comparative kinetic analyses of the mechanisms of toxicity of the alkylphenol eugenol and its putative toxic metabolite (quinone methide, EQM) were carried out in cultured rat liver cells (Clone 9, ATCC) using a variety of vital fluorescence bioassays with a Meridian Ultima laser cytometer. Parameters monitored included intracellular GSH and calcium levels ([Ca2+]i), mitochondrial and plasma membrane potentials (MMP and PMP), intracellular pH, reactive oxygen species (ROS) generation, and gap junction-mediated intercellular communication (GJIC). Cells were exposed to various concentrations of test compounds (1 to 1000 microM) and all parameters monitored directly after addition at 15 s intervals for at least 10 min. Eugenol depleted intracellular GSH, inhibited GJIC and generation of ROS, and had a modest effect on MMP at concentrations of 10 to 100 microM. At high concentrations (1000 microM), eugenol also affected [Ca2+]i, PMP, and pH. Effects of EQM were seen at lower concentrations (1 to 10 microM). The earliest and most potent effects of either eugenol or EQM were seen on GSH levels and GJIC. Coadministration of glutathione ethyl ester enhanced intracellular GSH levels by almost 100% and completely protected cells from cell death caused by eugenol and EQM. These results suggest that eugenol mediates its hepatotoxic effects primarily through depletion of cytoprotective thiols and interference in thiol-dependent processes such as GJIC. Furthermore, our results support the hypothesis that the toxic effects of eugenol are mediated through its quinone methide metabolite.

Animals↗
PubMed2005

Finite element model of cornea deformation.

Cornea surgeons have observed that changes in cornea curvature can follow cataract surgery and cause astigmatism. The placement of surgical incisions has been shown to influence these curvature changes. Though empirical data has been collected about this phenomenon, a biomechanical model has not been employed in predicting post-surgical outcomes. This work implemented an incised finite element model of the eye to investigate factors influencing corneal shape after surgery. In particular, the effects of eye muscle forces and intra-ocular pressure were simulated. Cornea shape change was computed via finite element analysis, and the resulting change in cornea curvature was measured by fitting quadratic curves to the horizontal and vertical meridians of the cornea. Results suggest that these two sources of deforming force counteract each other and contribute to astigmatism in perpendicular directions.

Astigmatism↗
PubMed1984

Muscular activity and perimetric thresholds.

Static and kinetic peripheral luminance thresholds were measured by means of a Goldmann perimeter along oblique meridians in monocular vision. In a main group of 33 young and healthy subjects these measurements and visual reaction time assessments were made successively at rest, when cycling without load, when cycling with load using aerobic energy supply, when cycling with load using anaerobic energy supply and twice again at rest. Another group of subjects did not pedal and served as controls. The results show that peripheral visual sensitivity increases faintly but significantly during muscular exercise. When assessed by static perimetry the sensitivity increase is grossly proportional with load and is thus greatest in anaerobic condition, while kinetic sensitivity differs by a sensitivity decrease when passing from aerobic to anaerobic exercise. The reported modifications in perimetric sensitivity during dynamic muscular exercise seem related to changes in alertness.

Adolescent↗
PubMedDate not supplied

The keratoconus epithelium studied by SEM.

A keratoconus removed from an 18-year-old male was processed for SEM and examined with special attention for the epithelial surface. A broad degenerative band was found running in the vertical meridian, showing areas devoid of, or with only partially attached, epithelial cells, and also areas with abnormal cells either, with a defective cell membrane and without cell contents or with an intact cell membrane but without a cell nucleus. Stereoscopic images of these defective cells show that cell degeneration is sometimes found several cell layers deep into the epithelium.

Adolescent↗
PubMed1989

Visual field in hysteria-reliability of visual field by Goldmann perimetry.

Four cases with hysterical amblyopia in youngsters under 15-year-old showed the poor reproducibility of visual field, that is, when the same target was moved from the periphery toward the fixation ten times along the same meridian during the same examination, the position of the plotted points were rather variable. The range of variation was measured from the innermost point to the outermost one, after the two first points were omitted because points first detected were usually far from the others. The variation of cases measured by this method was compared with that of normal persons. Results were as follows; 1. in normal person, the mean value of its range was 5.5 degrees in first decade and 4.2 degrees in second to seventh decade; 2. patients with psychogenic visual disturbances showed a variability of 14.2 degrees, and this was significantly different from normal (p less than 0.01). These results suggest that this convenient method was helpful for diagnosis of hysteria. It should also be remembered that when we evaluate the visual field, changes under 4 degrees are probably not significant.

Adolescent↗
PubMed1990

19th century mechanical models of eye movements, Donders' law, Listing's law and Helmholtz' direction circles.

Donders, Ruete, von Graefe, von Helmholtz, Listing, Volkmann and many others have provided the broad outline of an answer to the question how the eye rotates during eye movements. Many mechanical models of eye movements, ophthalmotropes, have been constructed and studied in the nineteenth century. These models have primarily served to explain Donders' and Listing's Laws on the nature of eye movements. As both Donders' Law and Listing's Law are easier to understand when seen against the background of the coordinate systems used to describe eye movements, all of the coordinate systems currently in use in the diagnosis and treatment of strabismus are described. In addition, the reader is introduced to a coordinate system based on von Helmholtz' direction circles, circles describing the direction of the horizontal and vertical retinal meridians in all positions of gaze.

Eye Movements↗
PubMed1990

The changing distribution of neurons in the inner nuclear layer from metamorphosis to adult: a morphometric analysis of the anuran retina.

The generation and changing distribution of neurons of the inner nuclear layer (INL) in the retina of two anuran species, Bufo marinus and Xenopus laevis, were studied from metamorphosis to adult. Morphometric studies were undertaken at six developmental stages in Bufo and four in Xenopus. The number and thickness of neurons in the INL were established in 29 predetermined retinal locations from serial sections of the eyes cut vertically or horizontally. The total number of neurons in the INL increased from metamorphosis to adult from 826,000 +/- 185 to 18,760,000 +/- 562 (mean +/- SD) in Bufo and from 308,000 +/- 25 to 877,000 +/- 31 in Xenopus. Over the same period the surface area of the INL increased about 50-fold from 2 mm2 to 96 mm2 in Bufo and 5-fold from 2.5 mm2 to 13 mm2 in Xenopus. In Bufo the difference between the highest cell number (central-temporal retina) and the lowest cell number in a sample area (dorsal and ventral peripheral retina) was 2.1:1 at metamorphosis. This ratio increased to 3.4:1 in the adult. Both the cell number and cell density per sample area in the INL was found to be higher along the nasotemporal meridian of the eye overlying the visual streak of the ganglion cell layer (GCL) of the retina. The retinal distribution of neurons in the INL did not change significantly during postmetamorphic growth in Xenopus. At metamorphosis a 1.7:1 difference was found between the highest neuron number (retinal ciliary margin) and lowest neuron number (retinal centre) decreasing to 1.5:1 in the adult. Retinae were labelled with 3H-thymidine in 15 mm Bufos and examined 2, 6, 12 and 18 weeks later. Higher rates of cell addition to the nasal and temporal poles of the INL were found compared with that at the dorsal and ventral poles. The retinal radial growth at the ciliary margin of the dorsal, ventral, nasal and temporal poles between the time of isotope injection and 18 weeks survival was found to be uneven; more radial elongation occurred at the nasal, dorsal and ventral poles and less at the temporal pole. These observations suggest that (a) the neuron distribution of the INL in adult animals approximates that of the GCL and (b) the visual streak-like area of the INL in Bufo develops by a sustained differential cell addition at the temporal and nasal poles of the retina.

Animals↗
PubMed1994

How many ganglion cells are there to a foveal cone? A stereologic analysis of the quantitative relationship between cone and ganglion cells in one normal human fovea.

Published studies on humans and monkeys show discrepancies in the reported quantitative relationship between cones (C) and ganglion cells (G). Data on human foveal retina suggest that it cannot accommodate the midget on-off system in addition to other functional channels. Foveal cell densities along the vertical meridian (0-1.8 mm eccentricity) were estimated in one normal human retina using the disector method. Cell ratios were calculated from cumulative total numbers. G density peaked at 0.65 mm eccentricity and C density at the foveola. Cumulative cell numbers showed a more rapid increase in G than in C with increasing eccentricity. G/C ratios of 2.7-3.4 were found using lateral displacement data modified from macaque. Using one estimate of displacement from the sections, the G/C ratio was 3.0. This study shows that there are on average three ganglion cells per foveal cone in humans, as in monkeys.

Adult↗
PubMedDate not supplied

Ultrasound biomicroscopic morphometry of the anterior eye segment before and after one drop of pilocarpine.

PURPOSE: To measure anterior eye-segment morphometric data using ultrasound biomicroscopy. This is a new high-frequency, high-resolution ultrasound method enabling the visualisation of the anterior segment of the living eye with magnification similar to a light microscope. METHODS: Thirteen morphometric parameters of the anterior eye segment were measured before and after the application of one drop of pilocarpine in 10 eyes of 5 persons, using a Zeiss-Humphrey Ultrasound Biomicroscope at a frequency of 50 MHz. In each session, 3 morphometric parameters in the central images (corneal thickness, anterior chamber depth, pupillary diameter) were measured 4 times, and 10 parameters in the radial images (scleral thickness, angle-opening distance, trabecular-iris angle, trabecular-ciliary process distance [TCPD], iris thickness, 1, 2 and 3, iris-ciliary process distance, iris-lens contact distance [ILCD], iris elevation) were measured on the 3, 6 and 9 o'clock meridians three times each. RESULTS: Statistically significant changes were noted in the following parameters: pupillary diameter, iris thickness 1 and 2, and TCPD were decreased, while ILCD was increased after pilocarpine. Wide chamber angles showed a tendency to become narrower and narrow ones to become wider after pilocarpine. CONCLUSION: One drop of pilocarpine caused significant changes in the anterior eye segment morphology. Not only the pupillary diameter decreased but iris thickness and trabecular-ciliary process distance were also decreased simultaneously. At the same time the contact surface between the lens and iris increased significantly. Ultrasound biomicroscopy gives new morphometric image information about the anterior eye segment which is not available using conventional gonioscopy or ophthalmic echography.

Administration, Topical↗
PubMed1988

Functional morphology of the ommatidia in the compound eye of the moth, Antheraea polyphemus (Insecta, Saturniidae).

The fine structure of the superposition eye of the Saturniid moth Antheraea polyphemus Cramer was investigated by electron microscopy. Each of the approximately 10,000 ommatidia consists of the same structural components, but regarding the arrangement of the ommatidia and the rhabdom structure therein, two regions of the eye have to be distinguished. In a small dorsal rim area, the ommatidia are characterized by rectangularly shaped rhabdoms containing parallel microvilli arranged in groups that are oriented perpendicular to each other. In all other ommatidia, the proximal parts of the rhabdoms show radially arranged microvilli, whereas the distal parts may reveal different patterns, frequently with microvilli in two directions or sometimes even in one direction. Moreover, the microvilli of all distal cells are arranged in parallel to meridians of the eyes. By virtue of these structural features the eyes should enable this moth not only discrimination of the plane of polarized light but also skylight-orientation via the polarization pattern, depending on moon position. The receptor cells exhibit only small alterations during daylight within the natural diurnal cycle. However, under illumination with different monochromatic lights of physiological intensity, receptor cells can be unbalanced: Changes in ultrastructure of the rhabdomeres and the cytoplasm of such cells are evident. The effects are different in the daytime and at night. These findings are discussed in relation to the breakdown and regeneration of microvilli and the influence of the diurnal cycle. They are compared with results on photoreceptor membrane turnover in eyes of other arthropod species.

Animals↗
PubMed1990

Topographic variations in W-cell input to cat superior colliculus.

Most of the retinal input to the cat's superior colliculus (SC) arises from W-cells of the contralateral eye and terminates just below the tectal surface. The goal of this study was to determine whether the strength of this input is uniform over the collicular map or, instead, exhibits topographic variations as has been reported for the retinotectal Y-cell projection (McIlwain and Lufkin 1976). Monosynaptic inputs from the principal W-cell projection mediate the late negative potential (LNP), a collicular field potential that can be evoked by shocks to the optic pathway. We assumed that the amplitude of the potential provided a measure of the strength of the W-cell input to the upper superficial gray layer. Using a fixed stimulus, we measured the maximal amplitude of the LNP at 90 topographically identified tectal sites in 5 cats. The amplitude of the LNP varied as much as 5-fold over the SC and was systematically related to the azimuthal position of the recording site. LNP amplitudes were consistently smallest in the representation of the area centralis and vertical meridian and largest in the representations of the contralateral hemifield periphery and the ipsilateral hemifield. There was little systematic variation in LNP amplitude as a function of elevation in the map. The observed variations did not result from non-uniform activation of retinal afferents or drift in properties of the recording electrodes, stimuli, or preparation. The results suggest that the principal W-cell input to the SC is weaker in the representation of the area centralis than elsewhere in the map.(ABSTRACT TRUNCATED AT 250 WORDS)

Action Potentials↗
PubMed1996

Combined eye-head gaze shifts to visual and auditory targets in humans.

We studied the characteristics of combined eye-head gaze shifts in human subjects to determine whether they used similar strategies when looking at visual (V), auditory (A), and combined (V + A) targets located at several target eccentricities along the horizontal meridian. Subjects displayed considerable variability in the combinations of eye and head movement used to orient to the targets, ranging from those who always aligned their head close to the target, to those who relied predominantly on eye movements and only moved their head when the target was located beyond the limits of ocular motility. For a given subject, there was almost no variability in the amount of eye and head movement in the three target conditions (V, A, V + A). The time to initiate a gaze shift was influenced by stimulus modality and eccentricity. Auditory targets produced the longest latencies when located centrally (less than 20 degrees eccentricity), whereas visual targets evoked the longest latencies when located peripherally (greater than 40 degrees eccentricity). Combined targets (V + A) elicited the shortest latency reaction times at all eccentricities. The peak velocity of gaze shifts was also affected by target modality. At eccentricities between 10 and 30 degrees, peak gaze velocity was greater for movements to visual targets than for movements to auditory targets. Movements to the combined target were of comparable speed with movements to visual targets. Despite the modality-specific differences in reaction latency and peak gaze velocity, the consistency of combinations of eye and head movement within subjects suggests that visual and auditory signals are remapped into a common reference frame for controlling orienting gaze shifts. A likely candidate is the deeper layers of the superior colliculus, because visual and auditory signals converge directly onto the neurons projecting to the eye and head premotor centers.

Acoustic Stimulation↗
PubMed1992

Viewing-distance invariance of movement detection.

Since visual movement information is often presented in electronic displays or films it is amazing that there is a paucity of research on the influence of viewing distance on motion detection in cinematograms. We report a relatively high degree of detection constancy with changing viewing distance for coherent motion in random-pixel cinematograms. A constant performance irrespective of viewing-distance is called 'distance-invariance' and for motion detection it proves to hold reasonably well for a relatively wide range of viewing distances both for foveal and eccentric vision. The limits of this viewing-distance invariance are explored as a function of screen velocity. Detection performance is quantified by a threshold signal-to-noise-ratio (SNR-) value, S, which is determined as a function of velocity for a range of viewing distances from 53 to 13,476 mm for foveal vision and from 60 to 1925 mm at 24 degrees eccentricity on the nasal horizontal meridian of the right eye's retina. The data can be explained, at least qualitatively, by a model in which a spatial-resolution stack has a stack of velocity-tuned motion detectors at every resolution layer. Such a 'stack-of-stacks' model is in line with proposals for contrast-detection stack-models, but it suggests that the usual hypothesis that motion perception is based on the activity of two separate systems, the short-range and the long-range system, might be superfluous. This two-systems distinction was largely based on the different performance found for moving random dot patterns and moving form-defined stimuli. A moving random pixel array viewed at very close range (e.g. 6 cm) presents the subject with relatively large almost square 'blobs', which are less dissimilar from the phi-stimuli used in classic motion perception studies than random dot stimuli at the usual medium to large viewing distances. It leads to maximum displacement threshold (Dm-) values that are not untypical of the 'long-range' system, but by gradually increasing the viewing-distance and thus decreasing the pixel-size a continuous change is found from typical long-range to typical short-range values of Dm. The two-systems distinction for motion detection appears to refer to the stimulus rather than to the visual system: The motion-detection system might be forced into a local or a global 'mode of operation' by the choice of stimulus.

Female↗
PubMed1991

Bilateral projections from the parabigeminal nucleus to the superior colliculus in monkey.

We examined the distribution of labeled neurons in the parabigeminal nucleus of the monkey following injections of retrograde fluorescent tracers into the superior colliculus. The extent of the visual field representation included in the injection site was assessed from the location of labeled cells in striate cortex. The results suggest a rough topographic organization of the parabigeminal nucleus, with the lower quadrant represented anteriorly and the upper quadrant posteriorly. We also found bilateral projections from the parabigeminal nucleus to both superior colliculi, but the crossed projection appeared to terminate only in that part of the colliculus where the vertical meridian is represented. Parabigeminal cells with a crossed projection were larger than those projecting to the ipsilateral colliculus. The results suggest that the organization of the monkey's parabigemino-tectal system is fundamentally similar to that of many other vertebrates.

Amidines↗
PubMed1985

Spatial interactions in the rhesus monkey retina: a behavioural study using the Westheimer paradigm.

For two trained rhesus monkeys, increment thresholds for a small test-spot of 100 ms duration were determined as a function of background size, at 10 retinal eccentricities along the horizontal meridian. Typical 'Westheimer-functions' were obtained, i.e. threshold first increases with increasing background size, reaches a maximum, then decreases with further increasing backgrounds and finally reaches a plateau. With increasing retinal eccentricities, the position of the peak of the functions is shifted towards larger background sizes, indicating an increase of perceptive field centre size from 0.25 degrees at 5 degrees eccentricity to 1.5 degrees at 40 degrees eccentricity. The perceptive field centres tend to be slightly smaller in the nasal retina. Total perceptive field sizes, as indicated by the beginnings of the plateaus, increase from about 1 degree near the fovea to about 3 degrees at 40 degrees eccentricity. The perceptive field centre sizes of two human observers, tested under the same experimental conditions, closely resemble those of the monkeys. The total perceptive fields are larger in the human subjects. The retinal ganglion cells determining threshold in this experiment are most likely the broad-band cells. The agreement between the behaviourally determined perceptive field centre sizes and the receptive field centre sizes of broadband cells (measured by DeMonasterio and Gouras 1975) is excellent. The dendritic fields of P-alpha-ganglion cells, most likely the morphological substrates of the broad-band cells (Perry, Oehler and Cowey 1984) are somewhat smaller at all eccentricities.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗