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E E Sutter

Publications and source records attributed to E E Sutter.

31 records · Page 2Linked to original sources
PubMed1990

Fundamental differences between the nonlinearities of pattern and focal electroretinograms.

We directly compared nonlinear kernels of normal human pattern electroretinograms (PERGs) and corresponding localized flash ERGs (FERGs). The FERG was triphasic and resembled an adaptive process because it decayed slowly without changing shape over several kernel orders and interpulse intervals. The PERG was biphasic in the slice nearest the diagonal of the second-order kernel, similar to the FERG in slices farther from this diagonal, and without power in higher-order kernels. The unique PERG features were short-term effects that immediately followed a contrast transition. The appearance-disappearance PERG had a triphasic first-order kernel and a biphasic second-order kernel. The latter was similar to, but half the size of, that for the contrast-reversal PERG. When the first off-diagonal slices of the two PERG second-order kernels were analyzed in detail, we found in both that the first positive peak was larger than the FERG at intermediate spatial frequencies. Both PERG peaks in the slice had a low contrast threshold and were linear with contrast. The three FERG peaks of the corresponding FERG slice had a higher threshold and were saturated with increasing contrast. These observations show that the PERG contains substantial pattern specific nonlinear components and cannot be dismissed as merely the nonlinear subcomponents of the corresponding FERG.

Contrast Sensitivity↗
PubMed1990

Lateral interaction component and local luminance nonlinearities in the human pattern reversal ERG.

Two different mechanisms are presumed to contribute to pattern electroretinograms: non linearities of the local luminance response and nonlinear effects of lateral interactions. Previous attempts to discriminate the two components relied on the theoretical MTF of the optics. In this study, techniques of nonlinear systems analysis are used to extract the two components from the response to pattern reversal of different check sizes. The decomposition is based on the structure of the second order pattern reversal kernels alone. Detailed information about the two mechanisms can be gleaned from the kernel structure. The component properties are compared and discussed.

Contrast Sensitivity↗
PubMed1985

Electrophysiological evidence for the existence of coarse and fine disparity mechanisms in human.

Visual sensitivity to stereoscopic disparity changes was measured both psychophysically and by means of evoked potentials. The binocular disparity of a dynamic random-dot stereogram portraying a single flat plane alternated between two values symmetrical about the plane of fixation. The threshold for disparity alternation of the stereoscopic plane was determined at alternation rates between 4 and 12 depth reversals per second (rps). Evoked potential and forced-choice psychophysical estimates of stereoscopic threshold at each reversal frequency agreed, with a mean discrepancy of only +/- 0.1 log units. Evoked potential amplitude was a linear function of log disparity up to about 15 arc min peak to peak disparity. For larger disparities, the evoked potential amplitude versus log disparity function was found to be nonmonotonic with a dip occurring at approximately 26 arc min disparity. Responses to fine disparities of less than 20 arc min lay close to one temporal phase while those evoked by coarse disparities greater than 40 arc min lay near a different phase. The data suggest that disparity processing mechanisms either undergo dynamic changes as disparity increases or that processing shifts between at least two independent mechanisms.

Depth Perception↗
PubMed1983

Trachoma in South Africa.

Trachoma remains the most common cause of preventable blindness in certain areas of the northern Transvaal region of South Africa. Results of epidemiological studies in the area indicate that trachoma is a familial disease with young children acting as the main source of infection within the family. Elderly women who have lived in these areas for long periods of time are at greater risk of blindness and impaired vision from the disease. Genital tract carriage of Chlamydia trachomatis is relatively infrequent in these trachoma-endemic areas and no evidence of eye-to-eye transmission of oculo-genital serotypes of C. trachomatis could be demonstrated.

Adolescent↗
PubMed1983

Community participation in the control of trachoma in Gazankulu.

Groups of villagers, the care groups, are involved in prevention and treatment of trachoma within their own communities. The effect of the scheme on standards of hygiene and prevalence of trachoma has been evaluated by randomised cluster sampling methods. The number of households who were digging refuse pits, acquired individual face cloths and were aware of the role of good hygiene in the prevention of trachoma exceeded significantly those in (control) villages without a care group, in contrast the acquisition of pit latrines showed an insignificant increase. The prevalence and intensity of active trachoma was found to be significantly reduced as a result of the intervention of the care groups. This scheme has been totally integrated into the primary health care system of the area.

Africa, Southern↗
PubMed1981

The epidemiology and geographical distribution of trachoma in Lebowa.

The prevalence of active trachoma and its potentially blinding sequelae have been estimated in ten settlements scattered throughout rural Lebowa. The disease represents a major public health problem only in northern Lebowa where 25% of subjects over 60 years of age were found to be suffering form visual disability as a result of the infection. Although the disease is endemic in most other parts of lebowa it rarely causes blindness and impaired vision. A rational approach to the control of trachoma in the area which takes into account both local considerations and recent advances in the knowledge of the epidemiology of the disease is recommended.

Adolescent↗
PubMed1979

The pathology of trachoma in a black South African population. Light microscopical, histochemical and electron microscopical findings.

Conjunctival biopsy specimens from a Black South African population suffering from trachoma have been studied by light microscopy, histochemistry and electron microscopy. A wide spectrum of histopathological changes was noted at different ages. Large cystically dilated glands containing concretions were seen and histochemical and electron microscopical examination revealed that the concretion material consisted of the inspissated secretion of goblet cells and cell debris. The cell damage seen in trachoma may be caused by the release of lysosomal enzymes from inflammatory cells.

Adolescent↗
PubMed1978

A community approach to trachoma control in the Northern Transvaal.

Trachoma represents the largest single cause of preventable blindness in the Black population of the Northern Transvaal. Epidemiological and cultural considerations indicate the necessity of community involvement in trachoma control at the household level. Involvement of the community by means of groups of voluntary health workers (care groups) has proved to be effective and acceptable to the local inhabitants. These groups, who form part of the comprehensive health system, integrate trachoma control into the primary health care activities of the area.

Community Health Workers↗
PubMed1978

Trachoma in a rural South African community.

The prevalence of trachoma was studied in a representative sample of family units from a rural community. Evidence of current or previous infection was found in 82% of the total population, but there was a relatively low prevalence of intense upper tarsal disease. Most children acquire the disease within the first 3 yr of life, these primary infections having a tendency towards spontaneous cure without complications. The prevalence of active disease and potentially blinding sequelae is higher in elderly females than in males of the same age. Clinical and microbiological evidence suggests that trachoma is transmitted primarily within households in this community, the main source of infection appearing to be children of pre-school age. Chlamydiae were isolated from the eyes of children with intense upper tarsal disease, but not from elderly persons with similar clinical signs.

Adolescent↗
PubMedDate not supplied

Retinotopic and nonretinotopic field potentials in cat visual cortex.

Two types of field potentials were identified in cat visual cortex using contrast reversal of oriented bar gratings: a short-latency fast-local component with a retinotopic organization similar to that seen with single-unit discharges at the same cortical site, and a slow, nonretinotopic component with a longer peak latency. The slow-distributed component had an extensive receptive field mapped by measuring the amplitude of binary kernels and showed strong inhibitory interactions within the receptive field. The peak latency of the slow-local component increased with distance from the retinotopic center, suggesting a possible conduction delay. Both components showed some orientation bias depending on the laminar location, but the bias could be independent of the orientation preferred by single units in the immediate vicinity. The present findings indicate that locally generated field potentials reflect cortical mechanisms for nonlinear integration over wide areas of the visual field.

Animals↗
PubMedDate not supplied

A topographic study of oscillatory potentials in man.

The purpose of this study was to evaluate the use of slow multifocal m-sequence stimulation in analyzing the topographic distribution and underlying mechanisms (including nonlinearities) of the retinal oscillatory potentials (OPs). In giving us access to the response topography and the nonlinear characteristics of the OPs, the m-sequence technique provides us with two important means for the identification and characterization of the signal sources. In this study, we analyzed the OPs into the first- and second-order components and investigated their topographies and luminance dependence. The distribution of both the first- and second-order OP components differed significantly from that of the flicker ERG investigated by Sutter and Tran (1992). At eccentricities and luminance levels favoring activity by both rods and cones, the second-order OPs were particularly prominent, showing the most clear-defined and complex waveform. The topographic distribution of the second-order OPs showed combined features of both rod and cone distributions. On a strong rod-bleaching background, the second-order OPs were eliminated and the first-order OPs showed a reduced amplitude and a shifted latency. These results are consistent with the notion that the second-order component of the OPs is dominated by contributions from rod-cone interactions.

Adolescent↗