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Biomedical subjects

E E Sutter

Publications and source records attributed to E E Sutter.

At least 19 recordsLinked to original sources
PubMed1999

[Multifocal electroretinogram (MF-ERG) in diagnosis of macular changes. Example: senile macular degeneration].

PURPOSE: Small areas of retinal pathology may pose diagnostic difficulties. The noninvasive multifocal electroretinogram (MF-ERG) provides a topographical mapping of retinal function. Its role in the diagnosis of macular diseases is examined in age-related macular degeneration (AMD). AMD is a main cause of central visual loss in the elderly population, affecting the second eye in 75%. METHODS: MF-ERG recordings of three patients with AMD were compared to the findings of fundus photography and fluorescein angiography. During the MF-ERG recordings the central 50 degrees of the retina was stimulated. The visual stimulus consisted of 241 hexagons that alternated, independently and pseudorandomly, between black and white according to a special predetermined binary sequence. Local retinal response components were extracted using the Fast m-Transform Algorithm. RESULTS: Three of six eyes had undergone cataract surgery with implantation of a posterior chamber lens (PCL). In accordance with an increase in light transmission through PCLs, these eyes showed an increase in the MF-ERG responses. MF-ERG allowed accurate topographic mapping of focal areas of retinal dysfunction in all patients tested. There was good correspondence to anatomical changes detected by fluorescein angiography. CONCLUSION: The high resolution of the MF-ERG enables detection of small areas of retinal pathology. It thus presents a clinically useful, noninvasive method in the early diagnosis and follow-up of macular disease.

Aged↗
PubMed1998

Assessment of local retinal function in patients with retinitis pigmentosa using the multi-focal ERG technique.

To assess local retinal function in patients with retinitis pigmentosa (RP), multi-focal ERGs and local thresholds (static visual fields) were obtained on eight RP patients with visual acuities of 20/25 or better. All eight patients showed multi-focal responses with normal timing within the central 5 deg. However, there were few responses with normal timing in the areas outside the central 7.5 deg, except in the case of the only patient with a 30 Hz full-field response with normal timing. Since full-field ERGs are dominated by responses from the periphery, this finding supplies a foundation for the commonly observed delays in the full-field cone ERGs of patients with RP. With respect to amplitude, only two patients showed multi-focal responses with near normal amplitudes anywhere in the field. The loss of amplitude at any point was not a good predictor of visual sensitivity in the Humphrey visual field. On the other hand, all areas with normal timing had near normal sensitivity. Timing changes appear to be an early indication of local retinal damage to the cone system. Nearly all areas with sensitivity losses greater than 0.5 log unit, and some areas with near normal sensitivity, showed significantly delayed multi-focal ERGs. Finally areas with extreme sensitivity loss show multi-focal responses with a wide range of amplitudes and implicit times across patients, suggesting different mechanisms of disease action in different patients.

Adult↗
PubMed1998

Lack of lateral inhibitory interactions in visual cortex of monocularly deprived cats.

To gain new insight into the effects of monocular deprivation, we studied the visual cortex of adult cats deprived of vision in one eye. Local field potentials were recorded in response to contrast reversal of square-wave gratings modulated in time either by pseudorandom, m-sequences or periodically. We have found that: (1) stimulation of the retinotopic locus of the recording site elicits responses with abnormal waveforms and long latencies from the deprived eye; (2) stimulation of a remote, non-retinotopic locus elicits responses from the non-deprived eye but not from the deprived eye; (3) the monocularly deprived cortex lacks lateral inhibitory interactions which are characteristic of the normal cortex; and (4) steady-state responses showed little difference in spatial-frequency tuning and contrast sensitivity between the deprived and non-deprived eye, mostly conforming to earlier field-potential data in monocular deprivation. Functional lateral interactions appear to be greatly reduced in monocularly deprived cortex.

Animals↗
PubMed1997

M and P components of the VEP and their visual field distribution.

To study components related to parallel processing of information across the visual field, multi-focal pattern reversal visual evoked potentials (VEPs) were recorded using binary m-sequences. Contrast, chromatic, spatial and temporal characteristics of the stimuli were varied in order to favor contributions from either M or P pathways. Responses were decomposed into two additive components whose behavior was consistent with that of M and P mechanisms. The results suggest that contributions to the VEP from the M pathway precede those from the P pathway, and that the ratio of P/M contributions decreases with eccentricity.

Adult↗
PubMed1997

Mapping of retinal function in diabetic retinopathy using the multifocal electroretinogram.

PURPOSE: To investigate focal abnormalities in the electroretinogram (ERG) signal in diabetic patients, with and without retinopathy, using a multifocal ERG. METHODS: Sixteen patients with diabetes mellitus, 8 of whom had diabetic retinopathy (mean duration of diabetes: 18.5 years) and 19 approximately age-matched healthy volunteers underwent multifocal ERG testing. One hundred three retinal locations within the central 50 degrees were stimulated concurrently, according to a pseudorandom m-sequence. Response components were extracted for each stimulated retinal location. RESULTS: In diabetic patients with retinopathy, the overall amplitudes were reduced (P < 0.01), and peak implicit times were increased (P < 0.01) in the first-order component (mean flash response) and in the first slice of the second-order component (local two flash interaction). In addition, local reductions of amplitude could be seen in the first- and second-order components. In patients without retinopathy, only amplitudes of the second-order component were reduced (P < 0.01). Another salient difference was observed in a special feature of the second-order component that was reduced in diabetic patients, with and without retinopathy (P < 0.05). CONCLUSIONS: Second-order components depend on nonlinear dynamics. Thus our findings indicate changes in the nonlinear dynamics of a fast-gain control in diabetic patients, presumably located in the inner retina. This suggests that early functional changes of the inner retina are evident in diabetic patients before impairment of the outer retina is observed. Multifocal nonlinear analysis permits the detection of subclinical diabetic retinopathy and offers the advantage of topographic mapping of retinal dysfunction.

Adult↗
PubMed1996

Imaging localized retinal dysfunction with the multifocal electroretinogram.

Conventional electroretinographic techniques do not permit efficient mapping of retinal responsiveness for the detection of small dysfunctional areas. This study explores the application of a new technique that makes such mapping possible. It utilizes a multifocal electroretinogram technique based on binary m sequences that simultaneously tests a large number of small retinal areas by multiplexing their responses onto a single signal derived from the human cornea. The focal responses are subsequently extracted for the derivation of high-resolution maps that characterize retinal responsiveness. The required recording times are short enough to make such testing feasible in the clinic. In this study we demonstrate the high sensitivity of the technique by mapping a small area that has been partially bleached by a strobe flash in a normal retina and by mapping dysfunctional areas in three patients with different, well-documented retinal pathologies. The results suggest that the multifocal electroretinogram has the potential to become a valuable clinical tool.

Adult↗
PubMed1995

Spatially distributed responses induced by contrast reversal in cat visual cortex.

Field potentials were recorded from cat striate cortex, either between an epidural screw electrode and a cannula-electrode inserted deep in the gray matter (transcortical recording) or with a pair of metal microelectrodes. Electrodes were placed bilaterally near the cortical projection of the area centralis. The horizontal separation of the recording tips was approximately 2 mm and approximately 300 microns, respectively. The area of the visual field providing input to the recording site (receptive field) was determined by measuring the field potentials generated by contrast reversal of high-contrast, achromatic bar gratings. Five-degree-diameter grating patches were presented individually over a large area of the visual field. The gratings were contrast-reversed at 4, 6 or 10 Hz, while also being swept in spatial frequency between 0.56 and 5.24 c/deg. The receptive fields were approximately 20 deg across or more, substantially larger than expected on the basis of cortical retinotopy. Responses were also elicited by stimulation of the hemi-field contralateral to that contributing to the classical receptive field, implicating the presence of a callosal projection. The large, spatially distributed receptive fields consisted of patches of high and low sensitivity. Continuous cortical infusion of either 100 microM tetrodotoxin or 10 mM muscimol at the recording site totally suppressed the transcortically recorded field potentials, proving that the local field potentials were generated postsynaptically. The present findings suggest that a cluster of cortical cells near the projection site of the area centralis receives input from remote cortical regions to an extent that is comparable with that of anatomically demonstrated long-range lateral connections.

Animals↗
PubMed1994

The topography of visual evoked response properties across the visual field.

Visual evoked potentials (VEPs) to luminance and pattern reversal stimulation were derived for a large number of small areas throughout the central visual field. In one study, the field was tested with a stimulus array consisting of 64 equal-area patches. Local response components were extracted by independent m-sequence modulation of the patches. Field topographies were compared between and within subjects using different electrode placements. The subject-dependent local variability observed in response characteristics is attributed to contributions from two or more cortical representations of the visual field and to inter-subject variations in gross cortical anatomy. The second study used luminance modulation of 56 patches across a 15 degrees field, scaled to activate approximately equal cortical areas in area V1. This produced many robust signals at all eccentricities. Bipolar and double differential ("1-dimensional Laplacian") signals were compared. The double differencing reduced contributions from distant or distributed sources, enhancing nearby current source activity, and greatly improved S/N for many stimulus locations. The high-resolution visual field maps demonstrated that clinical field testing using the VEP is not feasible because of effects of cortical convolutions on responses. However, the vast improvement in data quality and quantity make it a useful tool for VEP source localization and identification.

Brain↗
PubMed1992

The field topography of ERG components in man--I. The photopic luminance response.

A technique of multi-input systems analysis is used to explore the field topography of ERG responses to local luminance modulation. Variations in amplitude and wave form are studied within the central 23 degrees. Outside the fovea, the amplitude appears to follow a simple power law rx as a function of eccentricity r where x is approximately -2/3. The largest inter-subject variability is found in the fovea. Some nasal-temporal asymmetry is observed in all subjects with higher response densities in the temporal field outside the blind spot. The topography of the luminance response shares all these properties with the density of retinal cones.

Electrophysiology↗
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↗