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PubMed1994

Cryptosporidium oocysts in water for human consumption. Comparison of staining methods.

A study was carried out on the presence of oocysts of Cryptosporidium spp. in water for human consumption in the Province of Salamanca, Spain, using four different staining techniques: Ziehl-Neelsen, auramine, indirect immunofluorescence with monoclonal antibodies (Meridian, USA) and direct immunofluorescence with monoclonal antibodies (Pasteur, France). The presence of oocysts was detected in the water used for the washing of sand filters in the four water purifying plants and in the drinking water of two of the six geographical areas studied. The Ziehl-Neelsen and auramine staining techniques were found to have excellent diagnostic correlation. Immunofluorescence stainings with monoclonal antibodies proved to be less sensitive.

Animals↗
PubMed1992

Evaluation of a commercial enzyme immunoassay kit for the detection of Clostridium difficile toxin A.

A new enzyme immunoassay (EIA) kit developed for the rapid detection of Clostridium difficile toxin A in faecal specimens, Premier (Meridian Diagnostics), was evaluated using 101 faecal specimens. Sixty-nine specimens were positive for Clostridium difficile by isolation of the organism and by cytotoxicity in tissue culture. The EIA for toxin A was positive in 49 of these 69 cases. No specimen that was negative for cytotoxicity was positive by EIA. Eight of the 32 specimens negative by both EIA and cytotoxicity assay yielded Clostridium difficile by culture. In five of these cases the cytotoxigenic status of the isolate was determined, and four were positive. There was no direct relationship between cytotoxin titre and EIA reading.

Animals↗
PubMed1992

Evaluation of a new commercial Clostridium difficile toxin A enzyme immunoassay using diarrhoeal stools.

A new, commercially available enzyme immunoassay for the detection of toxin A in stool specimens, the Premier Clostridium difficile Toxin A test (Meridian Diagnostics), was evaluated using 228 diarrhoeal stool specimens. Using a cytotoxin assay on HeLa cells as the reference method, this new test resulted in a sensitivity of 88% and a specificity of 95%. Using the presence or absence of a toxigenic strain in the stools as the reference method, the sensitivity was similar to that of the cytotoxin assay (71.7+ versus 70.5%) and the overall correlation was even better (89.4% versus 82%). The Premier Clostridium difficile Toxin A assay is rapid and easy to perform and is an excellent alternative to the usual toxin B assay.

Bacterial Toxins↗
PubMed1988

Ocular torsion: sensorimotor principles.

Eye movements are basically limited to two degrees of freedom, as described by Donders' and Listing's laws. Complex patterns of innervation maintain the geometric constancy of the retinal meridians, presumably via visual feedback acting through orientation-specific neurons in the cortex. Interactions between torsional and vertical movements of the eyes can be demonstrated by stimulating ocular torsion and detecting secondary vertical deviations. Geometric considerations show that significant peripheral disparities occur with convergence and eye movements, dictating large Panum's fusional areas in the periphery. Good visual acuity in man must thus be limited to the fovea, but the large peripheral Panum's fusional areas allow sensory cyclofusion of up to 8 degrees. In addition, motor cyclofusion occurs in the presence of large-field stimuli, further helping to minimize problems from torsional diplopia both in normal individuals and in patients with ocular motor pareses.

Convergence, Ocular↗
PubMed1992

Laminar, columnar and topographic aspects of ocular dominance in the primary visual cortex of Cebus monkeys.

The representation of the two eyes in striate cortex (V1) of Cebus monkeys was studied by electrophysiological single-unit recordings in normal animals and by morphometric analysis of the pattern of ocular dominance (OD) stripes, as revealed by cytochrome oxidase histochemistry in V1 flat-mounts of enucleated animals. Single-unit recordings revealed that the large majority of V1 neurons respond to the stimulation of either eye but are more strongly activated by one of them. As in other species of monkey, neurons with preference for the stimulation of the same eye are grouped in columns 300-400 microns wide, spanning all cortical layers. Monocular neurons are clustered in layer IVc, specially in its deeper half (IVc-beta), and constitute less than 10% of the population of other layers. Neurons with equal responses to each eye are more commonly found in layer V than elsewhere in V1. In the supragranular layers and in granular layer IVc-alpha neurons strongly dominated by one of the eyes tend to be broadly tuned for orientation, while binocularly balanced neurons tend to be sharply tuned for this parameter. No such correlation was detected in the infragranular layers, and most neurons in layer IVc-beta responded regardless of stimulus orientation. Ocular dominance stripes are present throughout most of V1 as long, parallel or bifurcating bands alternately dominated by the ipsi- or the contralateral eye. They are absent from the cortical representations of the blind spot and the monocular crescent. The domains of each eye occupy nearly equal portions of the surface of binocular V1, except for the representation of the periphery, where the contralateral eye has a larger domain, and a narrow strip along the border of V1 with V2, where either eye may predominate. The orderliness of the pattern of stripes and the relationship between stripe arrangement and the representation of the visual meridians vary with eccentricity and polar angle but follow the same rules in different animals. These results demonstrate that the laminar, columnar and topographic distribution of neurons with different degrees of OD in V1 is qualitatively similar in New- and Old World monkeys of similar sizes and suggest that common ancestry, rather than parallel evolution, may account for the OD phenotypes of contemporaneous simians.

Animals↗
PubMed2003

Oculomotor consequences of feeble image size inequality at near reading distance.

Reading and working with a computer screen are activities of everyday life that take place at near vision. This study examines whether at such a near distance, normal subjects are capable of modifying the natural conjugacy of their saccades when exposed to a feeble image size inequality of 2%; similar inequality exists for persons who wear spectacles of slightly different power for the two eyes. Subjects were seated at 40 cm in front of a screen where a random dot pattern was projected. They were asked to make saccades of 7.5 degrees and 15 degrees along the horizontal and vertical principal meridians and horizontal saccades between secondary and tertiary positions in the upper and lower field. Five subjects performed the experiment with a 2% overall reduction lens inserted over their dominant eye; three subjects participated in a second experiment with an overall magnification lens of 2% also inserted in front of the dominant eye. The results showed a persistent decrease or increase in the size of the saccade of the dominant eye that was subject dependent for horizontal saccades, but consistent over subjects for vertical saccades. Persistent disconjugacy, at least for vertical saccades, is interpreted as evidence of learning.

Analysis of Variance↗
PubMed2003

Target similarity affects saccade curvature away from irrelevant onsets.

Saccade curvature away from visual distractors is a measure of the salience of these distractors for the oculomotor system. Three experiments are reported in which the integration of luminance onset signals and target similarity signals is examined, using a saccade curvature paradigm. Observers made saccades to a no-onset colour target in one of two positions on the vertical meridian. On most trials, an abrupt onset distractor that was either similar or dissimilar to the target appeared left or right on the horizontal midline. Saccades curved away from the irrelevant onsets; however, the amount of curvature was modulated by target similarity only when the onset appeared before the target (experiment 2) or when saccade initiation was delayed (experiment 3). These results suggest that the initial response to the onset is stimulus-driven and mediated by its transient component. Over time, the response is integrated with and augmented by top-down inputs. Visual and non-visual signals converge onto a common motor map to determine an item's salience.

Adolescent↗
PubMed2004

Underestimation of contralateral space in neglect: a deficit in the "where" task.

Space perception was investigated in right brain damaged patients with ( N=13) and without neglect ( N=5; control group). Patients were requested to localise a target tachistoscopically flashed at various eccentricities along the horizontal meridian. All patients had an intact visual field and spared ability to manually point to a target. To segregate magno- and parvo-pathway activity, stimuli modulated in either luminance or chromatic contrast were used. Patients were required to verbally report the stimulus position (verbal task) or to manually point to the stimulus (pointing task). Neglect patients reported the stimuli in the left visual field closer to the centre than they actually were. In the verbal test, underestimation was about 7 deg at the most eccentric position tested (20 deg), and decreased linearly for smaller eccentricities. The effect was similar but less marked in the pointing task. No difference was found for stimuli with luminance or chromatic contrast. Space underestimation was confined to the contralesional space; no evidence of misperception was detected in the ipsilesional hemifield. The present findings are consistent with the view that contralesional space representation is compressed in neglect patients.

Adult↗
PubMed2005

Loss of visual information in neglect: the effect of chromatic- versus luminance-contrast stimuli in a "what" task.

One to four vertical bars were tachistoscopically presented at various eccentricities along the horizontal meridian to patients with right brain damage and neglect (n=7) and to a control group of right brain damaged patients without neglect (n=4). Luminance contrast stimuli and isoluminant chromatic contrast stimuli were used. The patients' task was to report the number of bars. With luminance stimuli the neglect patients' discrimination in the left visual field was reduced, particularly at the most leftward position tested (ca 20 degrees ) where about 20% of the bars were omitted. The loss of information was limited to luminance contrast stimuli. When chromatic contrast stimuli were used, accuracy was comparable in the two hemifields and between groups of patients. The differential pattern of results for chromatic and luminance contrast stimuli is consistent with the hypothesis of a selective deficit of the magno-cellular pathway in neglect.

Aged↗
PubMed2005

Head-eye interactions during vertical gaze shifts made by rhesus monkeys.

Changing the direction of the line of sight (gaze) can involve coordinated movements of the eyes and head. During gaze shifts directed along the horizontal meridian, the contribution of the eyes and head depends upon the position of the eyes in the orbits; the contribution of the head to accomplishing the overall shift in gaze declines as the eyes increasingly are deviated away from the direction of the ensuing gaze shift. Also during horizontal gaze shifts, changes in the metrics and kinematics of the saccadic (eye movement) portion of coordinated movements, are correlated with the amplitude and velocity of the concurrent head movement. With increasing head contributions, saccade peak velocities decline, durations increase and velocity profiles develop two peaks. It remains unknown whether the interaction between head and eyes observed during horizontal gaze shifts also occurs during vertical gaze shifts. Yet, a full understanding of the neural control of eye-head coordination will depend upon the correlation of neural activity and features of vertical as well as horizontal movements. This report describes the metrics and kinematics of vertical gaze shifts made by head-unrestrained rhesus monkeys. Key observations include: (1) during vertical gaze shifts of a particular amplitude, relative eye and head contributions depend upon the initial vertical positions of the eyes in the orbits; (2) as head contribution increases, peak eye velocities decline, durations increase and vertical velocity profiles develop two peaks; (3) head movement metrics and kinematics are accurately predictable given knowledge only of head movement amplitude. In these ways, vertical gaze shifts were found to be qualitatively similar to horizontal gaze shifts. It seems probable that similar mechanisms mediate head-eye interactions during both horizontal and vertical movements. These observations are consistent with the hypothesis that a signal proportional to vertical head velocity reduces the gain of the vertical saccade burst generator.

Algorithms↗
PubMed2000

Direction-dependent distortions of retinocentric space in the visuomotor transformation for pointing.

The aim of this study was to: (1) quantify errors in open-loop pointing toward a spatially central (but retinally peripheral) visual target with gaze maintained in various eccentric horizontal, vertical, and oblique directions; and (2) determine the computational source of these errors. Eye and arm orientations were measured with the use of search coils while six head-fixed subjects looked and pointed toward remembered targets in complete darkness. On average, subjects made small exaggerations in both the vertical and horizontal components of retinal displacement (tending to overshoot the target relative to current gaze), but individual subjects showed considerable variations in this pattern. Moreover, pointing errors for oblique retinal targets were only partially predictable from errors for the cardinal directions, suggesting that most of these errors did not arise within independent vertical and horizontal coordinate channels. The remaining variance was related to nonhomogeneous, direction-dependent distortions in reading out the magnitudes and directions of retinal displacement. The largest and most consistent nonhomogeneities occurred as discontinuities between adjacent points across the vertical meridian of retinotopic space, perhaps related to the break between the representations of space in the left and right cortices. These findings are consistent with the hypothesis that at least some of these visuomotor distortions are due to miscalibrations in quasi-independent visuomotor readout mechanisms for "patches" of retinotopic space, with major discontinuities existing between patches at certain anatomic and/or physiological borders.

Adult↗
PubMed2000

Transneuronal retrograde degeneration of retinal ganglion cells following restricted lesions of striate cortex in the monkey.

Transneuronal retrograde degeneration of retinal ganglion cells follows extensive striate cortical removal in macaque monkeys. Its extent depends on the age of the monkey at operation, post-operative survival, species and retinal eccentricity. Some studies of human patients with occipital lobe injury have found no evidence for transneuronal retrograde degeneration, suggesting that either degeneration may not occur or, if present, it is caused directly by secondary damage impinging upon the underlying white matter or the blood supply to the dorsal lateral geniculate nucleus and optic tract. We therefore studied retinal ganglion cell degeneration in three macaques in which only the striate cortex corresponding to the macular retina had been removed, thereby sparing extrastriate cortex and precluding interruption of the vascular supply to the thalamus and optic tract. There was extensive loss of ganglion cells in the central retina, corresponding to the central 10 degrees of vision. As the cortical lesion was too small to affect the thalamus or optic tract directly, the retinal degeneration must be transneuronal. Quantitative analysis showed a 65-80% loss of ganglion cells in the corresponding perifoveal retinae along the horizontal meridian. The results confirm that the loss of retinal ganglion cells following striate cortical lesions is predominantly transneuronal.

Animals↗
PubMed2001

Neurons with large bilateral receptive fields in monkey prelunate gyrus.

In single-cell recordings from the dorsocaudal part of the prelunate gyrus of an alert monkey (Macaca fascicularis) we found neurons with unexpectedly large receptive fields (RFs) that spread bilaterally into the contra- and ipsilateral visual fields. These neurons (n=82) appeared to be clustered in the periphery of V4. They were surrounded by neurons with relatively small (3-10 degrees) and unilateral RFs in the contralateral field with properties similar to those previously described for neurons in area V4. Bilateral RFs extended over large parts of the lower visual field but always spared the fovea. Receptive fields typically revealed two foci of maximal responsiveness that were arranged symmetrically in the ipsi- and contralateral fields. Twenty-six cells did not respond to stimuli along the vertical meridian; these neurons had two distinct RFs. The preference for stimulus orientation, color, or motion was similar in all parts of these large RFs.

Animals↗
PubMed1998

Transient visual field defects induced by transcranial magnetic stimulation over human occipital pole.

Transient visual field defects (VFDs) and phosphenes were induced in normal volunteers by means of transcranial magnetic stimulation (TMS) using a circular magnetic coil of 12.5 cm diameter placed with its lower rim 2-4 cm above the inion in the midline. Subjects had to detect small, bright dots presented randomly for 14 ms in one of 60 locations on a computer screen resulting in a plot of the central 9 degrees of the visual field. In 8 of 17 subjects, transient VFDs were inducible at peak magnetic field strenghts of 1.1-1.4 T. In the central 1-3 degrees, detection of targets was impaired in both the upper and lower visual field, whereas at 4-9 degrees large parts of only the lower visual field were affected with a sharp cut-off along the horizontal meridian. Targets at 1 degree in the lower field were affected with lower TMS intensities than corresponding locations in the upper or peripheral locations in the lower field. Detection of central targets was affected at more caudal stimulation sites than detection of peripheral targets. Phosphenes were elicitable in 14 of 17 subjects at clearly lower field strengths of 0.6-1.0 T. Many subjects perceived chromatophosphenes. From a discussion of the literature on patients with VFDs and the known topography of the human visual system, it is concluded that the transient VFDs at 1-3 degrees are probably due to stimulation of both striate cortex (V1) and extrastriate areas (V2/V3), while VFDs in the lower visual field at eccentricities 4-9 degrees are due to stimulation of V2/V3 but not V1.

Adult↗
PubMed1999

Eye-position dependence of three-dimensional ocular rotation-axis orientation during head impulses in humans.

If horizontal saccades or smooth-pursuit eye movements are made with the line-of-sight at different elevations, the three-dimensional (3D) angular rotation axis of the globe tilts by half the vertical eye eccentricity. This phenomenon is named "half-angle rule" and is a consequence of Listing's law. It was recently found that the ocular rotation axis during the horizontal vestibulo-ocular reflex (VOR) on a turntable also tilts in the direction of the line-of-sight by about a quarter of the eye's vertical eccentricity. This is surprising, since, in a "perfect" VOR, the angular rotation axis of the eye should be independent from the position of the eye to fully compensate for the 3D angular head rotation. We asked whether this quarter-angle strategy is a general property of the VOR or whether the 3D kinematics of ocular movements evoked by vestibular stimulation would be less eye-position dependent at higher stimulus frequencies. Nine healthy subjects were exposed to horizontal head impulses (peak velocity approximately 250 degrees /s). The line-of-sight was systematically changed along the vertical meridian of a tangent screen. Three-dimensional eye and head movements were monitored with dual search coils. The 3D orientation of the angular eye-in-head rotation axis was determined by calculating the average angular velocity vectors of the initial 10 degrees displacements. Then, the difference between the tilt angles of the ocular rotation axis during upward and downward viewing was determined and divided by the difference of vertical eccentricity ("tilt angle coefficient"). Control experiments included horizontal saccades, smooth-pursuit eye movements, and eye movements evoked by slow, passive head rotations at the same vertical eye eccentricities. On average, the ocular rotation axis during horizontal head-impulse testing at different elevations of the line-of-sight was closely aligned with the rotation axis of the head (tilt angle coefficient of pooled abducting and adducting eye movements: 0.11+/-0.17 SD). Values for slow head impulses, however, exceeded somewhat the quarter angle (0.33+/-0.12), while smooth-pursuit movements (0. 50+/-0.09) and saccades (0.44+/-0.11) were closest to the half angle. These results demonstrate that the 3D orientation of the ocular rotation axis during rapid head thrusts is relatively independent of the direction of the line-of-sight and that ocular rotations elicited by head impulses are kinematically different from saccades, despite similar movement dynamics.

Adult↗
PubMedDate not supplied

Periareolar reduction mammaplasty utilizing the inferior dermal pedicle.

The critical points which should not be overlooked when performing reduction mammaplasty are to minimize scar on the breast and to ensure a sufficient blood supply for the viability of the nipple-areolar complex. Periareolar reduction mammaplasty has been widely used because it left only one scar around the areola. However, with the typical periareolar reduction mammaplasty technique, it is difficult to remove a large amount of breast tissue and mobilize the remaining breast tissue. It may result in necrosis of the nipple-areolar complex in some cases. To overcome these limitations we combined the periareolar incision with the inferior dermal pedicle, which has a relatively good blood supply. This new technique was employed in 22 consecutive women (44 breasts) with hypertrophy and a varying degree of ptosis. Infiltration of a tumescent solution and liposuction were performed in all cases. After periareolar incision, dissection of the skin was performed, and the breast was elevated from the fascia of the pectoralis major muscle, leaving the inferior dermal pyramidal pedicle. An adequate amount of tissue was resected in the superior, medial, and lateral areas. After mastopexy, closure was done with a purse-string suture. The amount of tissue resected ranged from 180 to 1510 g per breast, and the mean was 466.1 g. The mean length of elevation of the nipple was 10.6 cm along the meridian of the breast. There were a few complications which needed revision operation: hematoma collection in one breast (2.3%), wound dehiscence in one breast (2.3%), and fat necrosis in one breast (2.3%). There was no necrosis of the nipple-areolar complex. With this new technique of periareolar reduction mammaplasty utilizing the inferior dermal pedicle, we were able to minimize the scar, preserve the nipple-areolar complex, and improve the motility of the breast tissue. But we also observed a flat or square appearance in the case of a large amount of resection in the patients with poor skin elasticity. This technique is safe and versatile and produces aesthetically acceptable results in selected patients.

Adult↗
PubMed2002

[Sensory problems after macular translocation].

Following macular translocation, spontaneous compensation of subjectively felt tilt can occur by central adaptation to the rotation of the retinal meridians. However, in cases of large angle rotations or under binocular conditions, efforts to counter-rotate the globe have to be made in order to achieve comfortable vision. For restoring binocular vision postoperatively, the fusionable residual angle of 7-8 degrees should not be exceeded.

Adaptation, Ocular↗
PubMed1997

[Does the fundus perimetry determined edge of the blind spot depend on the superficial form of the papilla?].

BACKGROUND: We wanted to find out whether the borders of the blind spot depend on the surface topography of the optic disc and its surrounding area. PATIENTS AND METHODS: We therefore examined ten eyes with parapapillary atrophy adjacent to the temporal side of the disc. Fundus perimetry was performed under direct fundus control using a Rodenstock scanning laser ophthalmoscope. We examined the horizontal meridian of the optic discs in 0.5 degree steps using Goldmann IV-stimuli with 10 different degrees of brightness and the Goldmann stimulus 1, 0 dB (greatest luminance). Six eyes with symmetric, "normal" excavation served as controls. Optic disc topography was measured with the Heidelberg Retina Tomograph (HRT). RESULTS: Stimuli with a large luminance power (Goldmann IV, 4 dB) were seen up to 0.8 degree centrally (i.e., towards the optic disc center) from the temporal edge of the parapapillary atrophy, but up to 1.9 degrees centrally from the nasal optic disc border (P < 0.01). Horizontal HRT section profiles of the optic disc consistently showed prominent nasal disc borders contrasting with a shallow excavation within the temporal parapapillary atrophy. In all six subjects with a normally shaped disc there was no such "nasotemporal asymmetry." CONCLUSIONS: The size of scotomas depends on the surface topography of the tested area. The prominent nasal part of the optic disc appears less "blind" than the shallow temporal part, probably due to more intensive light scattering by the prominent nasal part of the disc.

Adult↗