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Biomedical subjects

F C Riemslag

Publications and source records attributed to F C Riemslag.

16 recordsLinked to original sources
PubMed1994

Autosomal recessive retinitis pigmentosa with preserved para-arteriolar retinal pigment epithelium.

Retinitis pigmentosa with preserved para-arteriolar retinal pigment epithelium is a rare form of retinitis pigmentosa that starts early in life with preservation of retinal pigment epithelium adjacent to and under the retinal arterioles and that has hitherto been described as an isolated form. We examined 22 patients from one large family, together with two isolated patients, and confirmed the presumed autosomal recessive mode of inheritance in this type of retinitis pigmentosa. New findings associated with retinitis pigmentosa with preserved para-arteriolar retinal pigment epithelium were asteroid hyalosis in four (17%) of 24 patients, tortuosity of retinal arterioles in 11 (46%) of 24 patients, peripheral regions of opacified vessels in eight (33%) of 24 patients, and preservation not only of the para-arteriolar pigment epithelium, but also of the peripheral retinal pigment epithelium in 13 (54%) of 24 patients. Previously reported signs present in these patients were nystagmus in six (25%) of 24 patients, hypermetropia in 23 (96%) of 24 patients, optic nerve head drusen in nine (38%) of 24 patients, vascular sheathing in 11 (46%) of 24 patients, maculopathy in all 24 patients (100%), yellow round deposits in the posterior pole in nine (38%) of 24 patients, exudates resembling those in Coats' disease in two (8%) of 24 patients, visual field defects in all 24 patients (100%), and nondeductible electroretinograms in 21 (91%) of 23 patients. Linkage analysis carried out in the large family resulted in the assignment of a gene for retinitis pigmentosa with preserved para-arteriolar retinal pigment epithelium to chromosome 1q31-q32.1.

Adolescent↗
PubMed1994

Thr4Lys rhodopsin mutation is associated with autosomal dominant retinitis pigmentosa of the cone-rod type in a small Dutch family.

A mother and daughter with autosomal dominant retinitis pigmentosa (adRP) were found to carry a cytosine-to-adenine transversion mutation at codon 4 of the rhodopsin gene. This mutation predicts a substitution of lysine for threonine at one of the glycosylation sites in the rhodopsin molecule (Thr4Lys). Both patients presented with a similar phenotype including a tigroid pattern of the posterior pole and a regional predilection for degenerative pigmentary changes in the inferior retina with corresponding visual field defects. The electroretinographic pattern was suggestive of RP of the cone-rod type. This report documents the clinical findings associated with this defined mutation of the rhodopsin gene.

Adult↗
PubMed1994

Morphology and function of the corneal endothelium after long-term contact lens wear.

PURPOSE: To examine whether corneal hydration control is impaired in corneas with endothelial morphologic changes (increased variation in cell size and cell angularity) due to long-term low gas-permeable contact lens wear. METHODS: Twenty-one long-term wearers of low gas-permeable contact lenses (mean age, 41 years +/- 8 SD) and 18 age-matched controls (mean age, 42 years +/- 8 SD) were studied. To assess endothelial morphology, endothelial photographs were taken, enlarged 400X, scanned into a computer, and evaluated. Hydration control was assessed by a corneal stress test. Corneal swelling was induced by applying low gas-permeable soft contact lenses for 2 hours during eye closure. After the lenses were removed, the rate of deswelling was determined using optic pachometry. RESULTS: Morphologic analysis of the endothelial photographs showed a significant increase of polymegethism (P < 0.01) and pleomorphism (P < 0.01) in the group wearing contact lenses compared with the control group. The percentage of recovery of corneal thickness per hour (PRPH) from induced swelling proved to be significantly lower (P = 0.03) and the induced swelling proved to be significantly lower (P < 0.01) in the group wearing contact lenses than in the control group. Multiple regression analysis showed that the PRPH decreased as the morphologic alterations increased. However, this trend appeared not to be significant at the 5% level. A significant relationship was found between morphologic parameters and induced swelling, indicating that induced swelling decreased as the morphologic alterations increased. CONCLUSION: The results of this study indicate that increased endothelial polymegethism and pleomorphism may be accompanied by a decreased corneal hydration control in people who wear contact lenses.

Adult↗
PubMed1992

Analysis of the electroretinogram in toxoplasma retinochorioiditis.

The decision to use therapy in toxoplasma retinochorioiditis depends on the location of the active lesion and the presence of vitreous activity. In eyes with dense vitreous clouding it can be difficult to see whether the macular region is involved or not. In theory the localisation of a lesion can be estimated on the basis of the flash ERG. The standard flash electroretinogram was recorded in 23 patients with inactive toxoplasma retinochorioiditis lesions in the retina. In 17 cases a lesion was present within the central 12 degrees of the visual field, 8 of these had a reduced photopic ERG. In 15 patients lesions were found outside the central 12 degrees, in 8 of whom the scotopic ERG was reduced. We conclude that the ERG can be of use in indicating the scar location in patients with dense vitreous clouding.

Adolescent↗
PubMed1992

Visual evoked potential estimation of visual activity with a Laplacian derivation.

Visual acuity was estimated with visual evoked potentials in 13 healthy subjects. A Laplacian derivation of 5 electrodes was used to improve the signal-to-noise ratio and to enhance striate cortical activity selectively. In 6 subjects, the Laplacian derivation gave a more reliable estimation of visual acuity than did a single midline derivation. In the other 7 subjects, the quality of both estimations was comparable.

Electrodes↗
PubMed1992

The application of Laplacian analysis in the recording of half-field pattern-onset evoked potentials.

The Laplacian operator in electroencephalographic measurements consists of a mathematical combination of the responses from a number of electrodes (e.g., five in a crosswise montage). It enhances activity from sources lying underneath the area covered, relative to activity from outside this area. Thus, by appropriate positioning, the contributions of extrastriate and striate sources can be recorded selectively. To quantify the contribution of each hemisphere to half-field onset evoked potentials, the responses in two Laplacian operators, one over each hemisphere, were analyzed and compared to monopolar derivations and a bipolar derivation between the two hemispheres. Both the Laplacian and bipolar analyses were helpful in interpretation of the responses.

Electrodes↗
PubMed1992

The laplacian analysis of the pattern onset response in man.

The pattern onset VEP described by means of principal component analysis was shown to be composed of at least two overlapping time components, of which one has a striate and the other an extrastriate origin. This analysis was based on a multi (24)-electrode registration. We looked for a technique that can distinguish, with a limited number of electrodes, between the striate and extrastriate components and can be applied in the clinic. The calculation of a 5-point 'Laplacian' operator over the striate area enhances the contribution of the striate source relative to the contribution of the extrastriate source that lies outside the area of the operator, and vice versa. We applied two 5-point operators, one centered on Oz and the other 6 cm left of Oz. This montage allowed for the selective recording of the striate and extrastriate activities separately. This was proved by means of an adaptation paradigm that selectively reduced the striate contribution. Application of the laplacian operator for clinical practice is exemplified by means of the VEPs of a patient suspected of psychogenic hemianopsia.

Brain↗
PubMed1992

Flicker electroretinograms: a systems analytic approach.

We observed multiple maxima and minima in the electroretinogram (ERG) first harmonics which varied as a function of adaptation level, mean illuminance, and modulation depth. Based on differences in response characteristics we identified a minimum of 3 parallel mechanisms operating at 3 frequency regions within the ERG: a low frequency region (less than 10 Hz), a midfrequency region (centered near 20 Hz), and a high frequency region (centered near 40 Hz). The low frequency region was observed both in dark- and light-adapted conditions, was basically linear, and showed nonlinear behavior only at high contrasts in either light or dark adaptation. It may be modeled as a low pass filter. The midfrequency region was clearly observed only above cone threshold, was nonlinear at low contrasts, and may be modeled as a linear filter followed by an essential nonlinearity. The high frequency region was observed under high levels of light adaptation and also was nonlinear at low contrast. It may be modeled also as a linear filter followed by an essential nonlinearity.

Dark Adaptation↗
PubMed1989

The electrooculogram: a refinement of the method.

The measurement of the light rise of the corneoretinal potential in the clinical routine depends critically on the constancy of the eye movements made by the subject. To verify to what extent the variability of the Arden ratio can be explained by the variability of these eye movements, an infrared scleral reflection technique was applied in order to monitor eye position and electrooculogram simultaneously. The data obtained in 10 normal subjects show that not only is the variability reduced substantially by correction for the actual eye movement, but also the routine procedure gives a systematic underestimation of the ratio. Monitoring eye movements makes available the use of eye movements of arbitrary size (e.g., optokinetic nystagmus), allowing for application of the method in uncooperative subjects such as children.

Adult↗
PubMed1988

On the origin of the presaccadic spike potential.

The spike potential (SP) accompanying the onset of saccadic eye movements has been reported to originate near the orbital region. Its dependence on saccade size, however, does not correlate with the behaviour of any of the possible sources of the potential available in the orbital region. The exact size dependence cannot be studied from results obtained with classical ENG methods to detect the saccadic onset and furthermore without removal of the artefact in the signal caused by the corneo-retinal potential. We recorded the SP by monitoring the eye movements with an infrared scleral reflection method (IRIS), and carefully studied the SP amplitude as a function of saccade size, and revealed a more realistic function. Furthermore, removal of the artefact of the corneo-retinal potential revealed a biphasic wave shape of the SP instead of the usually observed monophasic peak. These results support the hypothesis that this electrical activity accompanying the onset of saccadic eye movements originates in the oculomotor neurones innervating the ocular muscle units.

Action Potentials↗
PubMed1987

Are eye movement evoked potentials different from pattern reversal evoked potentials?

The averaged lambda wave elicited by saccadic eye movements across a checkerboard pattern has been reported to differ from checkerboard reversal evoked responses, even when the electroencephalographic responses were corrected for the artefact caused by the movement of the dipole moment of the eye itself. Because of these differences it was suggested that the recording of the lambda wave might provide extra information in pathological circumstances. We performed experiments in which the parameters of the pattern (high contrast checkerboard pattern, 20' checks, large field 72 x 72 degrees) shift across the retina were carefully adjusted. For instance, eye movements were made across an integer and odd number of checks in order to mimic the pattern reversal. Furthermore, the timing of the pattern movement in the pattern reversal condition was adjusted so as to simulate the saccadic eye movement. The results seem to suggest that the reported dissimilarities between pattern reversal and eye movement evoked responses can be accounted for by the small differences of the retinal shift in the two conditions.

Evoked Potentials↗
PubMed1986

Pattern ERG and glaucomatous visual field defects.

In the past five years numerous reports have suggested that ganglion cell function can be tested by means of a specialized form of electroretinography, the so-called pattern electroretinogram (PERG). Because of the important potentials of a ganglion cell test for clinical use this technique has been applied by several investigators to patients with (presumed) ganglion cell dysfunction, especially glaucoma. On grounds of principle we had reason to question whether the reported positive results should be attributed to ganglion cell dysfunction or to other factors such as optical disturbances. We investigated in this study the PERG as a function of visual field loss in glaucoma patients with careful control of optical factors. We did not find changes in PERG as a function of field loss. So either field loss is not related to the mass behaviour of ganglion cells, or ganglion cells are not the prime basis of the PERG. We believe the latter to be true.

Electroretinography↗
PubMed1985

Responses to paired onset stimuli: implications for the delayed evoked potentials in multiple sclerosis.

In multiple sclerosis (MS), demyelination is reported to be patchy and randomly distributed across the optic nerve, and a double peaked or broadened shape of the peaks of the pattern evoked potential would be expected. We tested quantitatively this hypothesis for our routinely recorded responses of MS patients. There was no significant broadening of the peak shape in the 75 prolonged latency responses. In order to simulate the patchy character of the affection of the optic nerve in MS, we tested 2 healthy subjects with a stimulus consisting of 2 presentations of a checkerboard pattern to different parts of the visual field, but with an adjustable onset asynchrony. It was found that, when the asynchrony was small (less than 40 msec) the second of the two stimuli did not contribute to the response. This suppression of the second response could be observed even when the second stimulus, by increasing its contrast, was made to evoke a much larger response than the first stimulus, when presented separately. Inhibition of the second response seems to explain the lack of wave shape alteration in the responses of MS patients, which would be expected on the basis of the patchy character of the demyelination. The responses from the fastest conducting fibres seem to determine the response, and inhibit the responses of the demyelinated fibres. From this, it can be concluded that a delayed response would be expected only in patients in whom a considerable number of the fibres of the optic nerve is affected by the demyelination. This seriously limits the sensitivity of the method for early diagnosis.

Adult↗
PubMed1985

The luminance origin of the pattern electroretinogram in man.

Electroretinograms (e.r.g.s) and visually evoked potentials (v.e.p.s) to pattern stimuli were recorded simultaneously from healthy subjects. The stimuli were produced by a configuration in which the luminance of two sets of spatial elements (checks) could be modulated independently. Experiments were designed to distinguish between contrast responses and non-linear luminance responses. In the first of two basic experiments, the luminance of only one set of checks was modulated, at a constant level in every trial. The other set was not modulated, but its luminance was set at various levels. Under these conditions the local luminance stimulation was kept equal for every trial whereas the contrast stimulation varied. Therefore, local luminance responses in these experiments were expected to be constant and contrast responses were expected to vary. The e.r.g.s were identical for all luminance settings of the unmodulated checks, suggesting that luminance rather than contrast determines the response. The v.e.p.s showed, on the contrary, the behaviour expected for contrast responses. In the second basic experiment the local luminance stimulation was also kept constant, but the phase difference between the modulations of the two sets of checks was varied between 0 deg (pure luminance stimulation) and 180 deg (pattern reversal). In this type of experiment the second harmonic responses to local luminance modulation are expected to decrease to a minimum as phase difference goes from 0 to 90 deg and increase again as phase difference goes to 180 deg. Contrast responses are expected to increase monotonically from zero to maximal at phase difference shifts from 0 deg (no contrast stimulation) to 180 deg (contrast reversal). The e.r.g.s decreased to a minimum at 90 deg phase difference and increase again with phase difference going to 180 deg. At 0 and 180 deg the same value was recorded. Consequently, the e.r.g. behaviour suggests a luminance origin of the responses. The v.e.p.s monotonically increased as phase difference went from 0 to 180 deg, thus suggesting a contrast origin of the responses. Two additional control experiments were performed. The first experiment compared the responses to homogeneous field red/green exchange and pattern red/green exchange, with the luminances of the red and green sources matched by heterochromatic flicker photometry. The exchange of luminance-matched red and green checks (pattern reversal) did not produce different e.r.g. responses from those recorded in response to homogeneous field red/green exchange. The v.e.p. showed a significant increase for the pattern stimulus.(ABSTRACT TRUNCATED AT 400 WORDS)

Color Perception↗
PubMed1982

Pattern evoked potential diagnosis of multiple sclerosis: a comparison of various contrast stimuli.

1. The transient and steady-state reversals seem to give equivalent information. 2. Random presentation of pattern reversals evokes the same response as conventional repetitive stimulation. Since random stimulation abolishes rhythmic activity, it is the most efficient stimulus form to generate a reversal response. 3. The pattern onset-offset stimulus is preferred for clinical application, since this stimulus is more efficient in evoking a contrast-evoked potential. 4. The absence of an evoked potential should never be used as a positive diagnostic criterion in MS.

Diagnosis, Differential↗