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W Spileers

Publications and source records attributed to W Spileers.

At least 37 records · Page 2Linked to original sources
PubMed1996

Colour contrast thresholds are normal in functional amblyopia.

We evaluated colour contrast thresholds in patients with unilateral functional amblyopia. A computer-controlled colour vision test was used to determine colour contrast thresholds along a blue-yellow tritan axis. Prior to the threshold measurement, a heterochromatic flicker brightness test was performed to ensure isoluminance between the test stimulus and the background for every subject individually. Luminance contrast thresholds were also measured using the same computer-based system. Twenty amblyopic patients were tested. All showed normal tritan colour contrast thresholds both for their amblyopic eye and non-amblyopic fellow eye. Luminance contrast thresholds were elevated in all 6 refractive amblyopic eyes, in 4 of 9 strabismic eyes and in 2 of 5 mixed amblyopic eyes. Colour contrast thresholds are normal in functional amblyopia (with central fixation). Whenever elevated tritan colour contrast thresholds are found in patients with a decreased visual acuity, other causes of visual impairment are to be evaluated.

Adolescent↗
PubMed1996

Leber congenital amaurosis--differential diagnosis, ophthalmological and neuroradiological report of 18 patients.

Between 1985 and 1995 eighteen babies, presenting to our department with absent visual contact and roving eye movements, showed a non-recordable flash electroretinogram (fERG). This was confirmed when repeated after a one-year interval. In four patients with developmental delay an underlying systemic disorder was diagnosed after a thorough pediatric neurological evaluation: Senior Loken syndrome, neuroaxonal dystrophy, ceroid lipofuscinosis and a yet unclear metabolic disorder were the revised diagnoses. The fourteen remaining patients were diagnosed as having primary idiopathic Leber Congenital Amaurosis (LCA). Three of them showed developmental delay. In all three cerebellar abnormalities were visualized on brain computed tomography (CT) and/or magnetic resonance imaging (MRI). Brain CT of the other eleven patients with age appropriate development was normal. We conclude that LCA is a diagnosis of exclusion and a cautious approach with a thorough history and pediatric neurological examination is necessary to exclude a more global pediatric neurological disorder.

Belgium↗
PubMed1996

Evolution of ophthalmic and electrophysiological findings in identical twin sisters with the carbohydrate deficient glycoprotein syndrome type 1 over a period of 14 years.

AIMS: To evaluate the evolution of ocular and electroretinographic findings in identical twin sisters with the carbohydrate deficient glycoprotein (CDG) syndrome over a period of 14 years. METHODS: Both girls underwent a clinical ophthalmic examination with funduscopy and an electrophysiological assessment with recording of flash electroretinogram (FERG) at the age of 4 years and 18 years RESULTS: On ophthalmic examination at the age of 4 years an alternating convergent squint and a saccadic pursuit was diagnosed. In both, vision was 6/9 bilaterally. Fundus examination showed normal optic discs, narrow blood vessels, and a mild irregular pigmentation in the periphery. In one girl the FERG showed a recognisable a, b1, and b2-wave with reduced amplitude to less than 40% of the normal. In the other girl the reduction in amplitude was still more obvious, but for the white flash a small b1-wave was still present. At the age of 18 vision had remained 6/9 in both eyes. Funduscopy showed pink optic discs, moderately narrowed blood vessels, and bony spicule pigmentary deposits in the mid periphery. The adapto ERG, performed in identical conditions at 18 years of age, showed a completely extinguished trace for both eyes. CONCLUSIONS: Despite progressive deterioration of ERG findings good central vision was preserved over 14 years.

Congenital Disorders of Glycosylation↗
PubMed1996

Pelli-Robson contrast sensitivity test in Zaire.

The purpose of this study was to establish in this first report the age standards of the Pelli-Robson contrast sensitivity in Zaïre. Contrast sensitivity using the Pelli-Robson chart was performed in 100 normal Zairian black subjects aged from 10 to 59 years and 36 patients (22 patients with open-angle glaucoma and 14 with optic nerve disease). Scores of normal subjects were age related (p < 0.05). The results of Zairian young subjects were similar to those found previously in young white subjects; scores for older subjects were lower when compared to those of whites. Scores of patients were lower than those of normals (p < 0.001). Contrast sensitivity using the Pelli-Robson chart can be useful in developing countries.

Adolescent↗
PubMed1995

Quadrant analysis of peripheral colour contrast thresholds can be of significant value in the interpretation of minor visual field alterations in glaucoma suspects.

Peripheral colour contrast thresholds were investigated in glaucoma suspects with no or minor visual field alterations, determining the average colour contrast threshold at 12.5 degrees off axis. The technique was introduced as a rapid screening test for pre-glaucomatous visual loss. Using this 'ring' test, all definite glaucoma patients in the initial study had elevated colour contrast thresholds. In our experience, however, a substantial proportion of early glaucoma patients were found to have normal thresholds. The peripheral colour contrast threshold determined by the ring test is an average threshold in the entire annular zone at 12.5 degrees eccentricity. We therefore modified the test procedure without a major increase in test duration. An arcade subtending 45 degrees at 12.5 degrees eccentricity was used to determine colour contrast thresholds in four quadrants of the visual field separately ('quadrant' test). We present here the first results of this novel procedure, investigating peripheral colour contrast thresholds in glaucomatous patients. The quadrant test is shown to be more sensitive than the ring test in the detection of functional loss.

Adult↗
PubMed1994

Contrast modulated steady-state visual evoked potentials (CMSS VEPs): recording evoked potentials and related single cell responses in area 17 of the cat.

(1) The functional characteristics of the neuronal substrate, responding to the CMSS VEP stimulus, were studied by recording CMSS VEPs and related single unit activity in area 17 of the anaesthetised and paralysed cat. CMSS VEPs use an 8 Hz phase reversing (i.e., 16 reversals/sec) grating stimulus with rapid contrast sweeping and allow the contrast thresholds and lag values to be measured as a function of the spatial frequency. (2) The CMSS VEPs of the anaesthetised cat have a wave form similar to those of humans but are shifted to lower spatial frequencies, higher contrast thresholds and longer lag values. (3) The cellular response to a sinusoidal grating, phase reversing at 8 Hz, was studied in order to identify the neuronal substrate generating the CMSS VEPs. Sixty percent of the area 17 cells respond to this stimulus. Cells responding at 8 Hz reversal comprise a distinct subpopulation of visual cortical cells selective for higher velocities and lower spatial frequencies. (4) Although the CMSS VEPs contain almost exclusively energy at 16 Hz, the temporal response pattern of striate cells is quite disparate, including first and second harmonic response patterns as well as an intermediate type. (5) There is a near-perfect correlation between the contrast thresholds of single cells, obtained with the contrast swept stimulus and those obtained with a static contrast test, validating the technique of rapid linear contrast sweeping. (6) The influence of the temporal parameters of the contrast sweeping on the calculated contrast threshold was investigated at the neuronal level. These parameters only marginally influence the responses. (7) CMSS VEP contrast thresholds and neuronal thresholds were compared. The sensitivity of VEPs corresponds to that of the most sensitive neuronal generators. CMSS VEP lag values are longer than the values for individual neurones.

Animals↗
PubMed1994

Optic atrophy as the presenting sign in Hallervorden-Spatz syndrome.

A girl of eight years of age is described with the Hallervorden-Spatz syndrome. Optic atrophy with progressive visual loss was the only presenting symptom for three years. Behavioural and motor disturbances emerged after that time. Optic atrophy can be the first and for some time only symptom of the Hallervorden-Spatz syndrome.

Brain↗
PubMed1994

[The Farnsworth-Munsell 100 Hue test in the Bantu population. Preliminary results].

The purpose of this work was to establish in this first report the age standards of the Farnsworth-Munsell 100 hue in Zaire. The Farnsworth-Munsell 100 Hue test was performed in 132 normal subjects. All subjects were Zairian blacks aged from 20 to 49 years. The test was administered binocularly, once, to each subject. Subjects were divided in three age groups. The first age group had 35 subjects aged between 20 and 29 years, the second age group had 48 subjects aged between 30 and 39 years and the third 49 subjects aged between 40-49 years. The total error scores were 7.06 +/- 2.10 for the first age group, 9.03 +/- 1.80 for the second age group and 9.80 +/- 2 for the third age group. These results were aged related (r = 0.42, p inferior to 0.05). Scores of Zairian subjects in this study were higher when compared to those reported in Europe and U.S.A. Interpretation of results of the Farnsworth-Munsell 100 hue test must take in account this difference in ethnic origin.

Adult↗
PubMed1993

Evidence from human electroretinogram A and off responses that color processing occurs in the cones.

PURPOSE: To investigate two apparent anomalies of the human electroretinogram: the "on" and "off" components of the cone based PIII are unequally sized, and transitions from red to green, which are electroretinographically silent, yield reverse transitions (green to red) in which a-waves develop. METHODS: Ganzfeld electroretinograms were obtained with intense 100 msec flickering flashes from red and green light-emitting diode. Such stimuli light-adapt the retina, and the responses are caused by the excitation of long and medium wavelength cones. RESULTS: In the 10-20 msec after the beginning of a flash (black to green or black to red) the beginning of rapid receptor-generated a-wave is seen. Ten to twenty milliseconds after the end of the flash, the beginning of a rapid positive-going off response, also derived from receptors can be seen. If the retina is stimulated by the abrupt change from one wavelength of light to another (eg, from "green" to "red"), at times > 20 msec after the change there are always slow changes in potential (presumably caused by postsynaptic activity) regardless of the relative intensities of red and green. However, if the two light intensities are adjusted appropriately, 10-20 msec after the transition from green to red no electroretinographic a-wave (or off response) develops--the transition is "silent." When the transition reverses (changes back from red to green), an a-wave occurs. In the same way if a red-to-green transition is made silent by altering the relative light intensities, the green-to-red reversal evokes an a-wave. This occurs for numerous pairs of red and green intensities. Rod intrusion or minor electroretinogram components do not explain this result. The relative red:green intensity in two color-anomalous subjects is different to that in three normal subjects. The rule for a silent transition is that the decrease in excitation in one cone type should be twice the increase in excitation in the second cone type. CONCLUSIONS: The most likely cause is a reduction in the amplitude of cone receptor potentials 20-50 msec after the onset of the stimulus, caused by a sign-reversing feedback mechanism such as that described in amphibians. This implies that the chromatic signals for color vision required by theorists are partly generated in the cones.

Color Perception↗
PubMed1991

Macular colour contrast sensitivity in ocular hypertension and glaucoma: evidence for two types of defect.

Colour contrast sensitivity (CCS) of a large cohort of glaucomatous patients, ocular hypertensive patients (OH), and normal persons was measured at six-month intervals during a two-year period. The OHs were graded into high, medium, and low risk groups. 69% of glaucomatous patients and 32% of all OHs had CCS thresholds greater than the mean plus 2 SDs of the controls. Satisfactory specificity and sensitivity could not be obtained by adjusting the criterion of threshold. In abnormal eyes, progressive small increases of threshold occurred during the study, but glaucomatous eyes with normal thresholds on the first visit retained normal thresholds in the subsequent visits. Although our system is very sensitive and precise, the proportion of abnormalities detected is no greater than with other techniques. In some glaucomatous patients there is a true preservation of colour vision which does not merely reflect the limitations of the test employed.

Color Perception↗
PubMed1991

Peripheral color contrast. A new screening test for preglaucomatous visual loss.

A new test of peripheral color contrast is described. A high-definition color monitor driven by a personal computer with a graphics interface card displays an annulus subtending 25 degrees at the eye. The color contrast between the annulus and the background can be varied. Forty-five degrees of the annulus is randomly removed in one of four quadrants. Patients are asked to identify the position of the gap while fixating a central spot. The minimum color contrast between annulus and background at which the identification is possible is between 13-16% for the protan, deuteran, and tritan axis in normal subjects. This threshold value changes little with age, refractive error, or pupillary aperture, and test-retest variability is low. Testing one eye takes only 1-2 min. The test was applied to ocular-hypertensive and glaucomatous patients. All patients with glaucoma had thresholds greater than two standard deviations (SD) above the normal mean. In addition, 97% of glaucoma patients had thresholds greater than four SDs, and 95% had thresholds more than five SDs above the normal mean. Most patients with ocular hypertension and clinical signs indicating a low or medium risk of conversion to glaucoma had thresholds under the upper limit of normal. High-risk patients with ocular hypertension fell into two groups. One approximated to normal; the other had elevated thresholds, which in many cases were more than four SDs above the normal mean. The epidemiologic consequences of this test are discussed.

Adult↗
PubMed1990

Modulation by a moving texture of cat area 18 neuron responses to moving bars.

1. The influence of a moving texture on neuronal responses to a moving bar was tested in 103 area 18 neurons of anesthetized and paralyzed cats. The texture was a two-dimensional noise pattern, the bar moved at optimal speed, and its contrast was adjusted to yield 50% of the maximum response. 2. The moving texture exerted two different but related effects: it suppressed the response of area 18 neurons to the moving bar, and it modulated the direction selectivity of parastriate neurons. These effects were strongest when the texture moved at the same speed or faster than the bar. 3. Genuine suppressive effects of the moving texture were distinguished from lack of summation between bar and texture responses. Suppressive effects of either type were observed in 75% of the area 18 cells and occurred more frequently among C family cells, velocity tuned cells, and in layer 5 than in other groups of cells. 4. The modulation of direction selectivity was distinguished from pseudomodulation because of lack of summation of bar and texture responses. The direction selectivity of 35% of the area 18 cells was modulated by the moving texture. Six different relative direction selectivity (RDS) types were observed in area 18. 5. The neurons of which direction selectivity was modulated by the moving texture occurred predominantly in layers 2-3 and 6, suggesting that they represent a further stage of processing within area 18. 6. Many (75%) area 18 cells responded to the texture moving on its own. Most of these cells respond to isolated features ("grains") in the patterns rather than to the movement of the whole pattern. Cells responding to the movement of the whole pattern were generally C family cells, and their direction selectivity was not modulated by the moving texture. 7. These results are compared with those obtained under identical experimental conditions in area 17. Although suppressive effects are similar in both areas, RDS types are differently distributed in the two areas. 8. The possible origins of the interactions and their functional significance are discussed.

Animals↗
PubMed1990

Selectivity of cat area 18 neurons for direction and speed in depth.

1. Fifty-eight area 18 cells recorded in anesthetized and paralyzed cats were tested for selectivity for direction in depth after their monocular velocity characteristics and static disparity profile were determined. 2. Direction in depth was produced by changing the speed and direction in the two eyes, but keeping the speed along axes in depth constant. 3. Forty-two cells were completely investigated, which means that direction in depth selectivity was tested at least at two different position disparities and two different bar speeds. Seven out of the 42 cells were accepted as direction in depth selective. 4. The 16 remaining cells were incompletely tested. Only one of them was direction in depth selective at the disparity and speed tested and shared all the properties of the seven completely tested direction in depth selective cells. Therefore we estimated that 8/58, i.e., 14% of the area 18 cells are direction in depth selective. 5. The direction in depth selective cells are a very homogeneous class: they all belong to the S family, are velocity tuned, monocular, prefer orientations close to vertical, and have a broad inhibitory or an unmodulated position disparity profile. 6. Direction in depth selectivity arises both from monocular properties and binocular interactions. These binocular interaction profiles can be symmetric or asymmetric. The change of these interaction profiles with changes in base speed can be summarized as changes in level of inhibition for the axes corresponding to equal speed in the two eyes on one hand and changes in the slope of the inhibition gradient centered on these axes of equal speed on the other hand. 7. Nineteen of the 58 cells were tested for selectivity for speed along trajectories in depth. All five direction in depth selective cells tested were also tuned to speed in depth. This suggests that area 18 contributes to the elaboration of a 3D velocity map. 8. A wiring diagram that accounts for the binocular interactions underlying direction selectivity in depth is presented.

Animals↗
PubMed1989

The response variability of striate cortical neurons in the behaving monkey.

In order to relate single cell performance to behavioral discrimination one needs measurements of the response variance of the units. We recorded from 183 single units of area V1 of monkeys performing an orientation discrimination task. The response variance was found to increase with increasing response strength. This relationship between response variance and response strength was well described by a power function with a power close to one. The response variance was on average 1.9 times the response strength. Despite important differences in preparation, the behaving monkey data are in good agreement with those previously obtained in paralysed and anesthetised animals.

Animals↗