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Biomedical subjects

I Wilmanns

Publications and source records attributed to I Wilmanns.

At least 19 recordsLinked to original sources
PubMed1991

[Standardized determination of pressure tolerance of the optic nerve head].

The early diagnosis of glaucoma relies on the detection of manifest damage in present-day clinical practice. The reason for such damage in glaucoma may be seen in the breakdown of the autoregulation of the circulation in the optic nerve head. This autoregulation can be assessed by the pressure tolerance test devised by ourselves which may detect glaucoma before manifest damage can occur. We demonstrate a standardized method in which the test procedure is controlled by a computer. In particular, the time course of the examination which is of crucial importance is exactly defined. The method is no more difficult to apply than automatic perimetry. We describe six examinations in seven subjects each. The results are analyzed by the estimation of variance components. The intraocular pressure shows an intraclass correlation of 0.41 and the critical pressure an intraclass correlation of 0.27. The intraindividual variability of critical pressure is mainly due to the widely known variability of intraocular pressure. The autoregulation behavior shows a very good constancy, which makes the test clinically useful in the differential diagnosis of glaucoma.

Adult↗
PubMed1990

[Total average values of transient visual evoked cortical potentials in tests of the pressure tolerance of the optic nerve].

Transient visually evoked cortical potentials were recorded during an artificial stepwise rise of intraocular pressure. At each pressure step one average was taken. The reversal rate was 1.9 Hz. Two groups of 30 healthy volunteers each were examined: in group one 25 sweeps were averaged and in group two 50 sweeps. Thus the recording time in group two was doubled compared to group one. When all subjects were examined the evoked potentials of the 30 subjects were averaged at each pressure step: the results was a "Grand Average" at the different pressure steps applied. The amplitudes of N2-P2 were plotted versus the intraocular pressure. It is seen that a not monotone or weakly monotone function in the amplitude/pressure curve is more clearly seen in the averages of 25 sweeps. We interpret this result as follows: a not monotone or weakly monotone behaviour is a sign of autoregulation in the optic nerve head. This sign is more clearly shown at a short recording time. The majority of healthy persons show autoregulation, the majority of glaucoma patients do not. According to the results presented here it is advisable to apply short recording times in clinical pressure tolerance testing of the optic nerve head. A short recording time enhances the accuracy of the test.

Adult↗
PubMed1990

[The pressure tolerance test--a new technic in the differential diagnosis of glaucoma].

There can be a damage of optic nerve fibers without a known increase of intraocular pressure. This observation has led to the proposition to measure the pressure tolerance of the optic nerve head. An examination which is performing this task is feasible now with a recently introduced technique. In this paper clinically well defined borderline cases are presented in which the pressure tolerance test yields clinically valuable results. As shown paradigmatically the pressure tolerance test shows to be a valuable tool in the differential diagnosis of glaucoma.

Adult↗
PubMed1989

Automated corneal topography: computerized analysis of photokeratoscope images.

The analysis of corneal topography has recently become popular, mainly as a consequence of the rapid development of refractive surgery techniques. To date, computer-assisted evaluation of photokeratoscope pictures has been the most popular method used to assess corneal topography. The processing system described previously by other authors requires hand-digitizing of the photokeratoscope pictures and therefore the constant presence of an operator for a considerable amount of time. We have introduced the use of a video camera to digitize the photokeratoscope images, making the processing automatic and quicker. Moreover, precision glass spheres have been used to calibrate the system in order to minimize the intrinsic errors even further. The data obtained from the computerized analysis are presented in three different ways. Besides having the numerical values in diopters, corneal maps with various shades of grey are used, together with the quantitative, three-dimensional representation of corneal astigmatism. An automated system for the analysis of corneal topography was tested for both experimental models and clinical conditions. It was easy to use and showed high precision (less than 1% error when processing photographs of precision glass spheres).

Cornea↗
PubMed1989

[Effect of carteolol and timolol eyedrops on the pressure tolerance of the optic nerve head].

In a planned, randomized, double blind study ocular perfusion pressures were measured before and after a 3-day regimen of 2% carteolol hydrochloride or 0.5% timolol maleate. A pressure tolerance test was also carried out. The results of this test revealed the critical pressure: it is the artificially increased intraocular pressure at which the visual function (monitored by visually evoked cortical potentials) is reduced to 20% of its initial value. The ocular perfusion pressures are affected by both drugs. They are more clearly reduced by carteolol than by timolol. The critical pressure is affected by both drugs too. After application of carteolol, the critical pressure is clearly lower than after application of timolol. The difference is statistically significant (p less than 0.05).

Adaptation, Physiological↗
PubMed1988

Nd:YAG laser shock waves in artificial eyes.

Nd:YAG laser surgery is performed by inducing optical breakdown in the interior of the eye. The optical breakdown is accompanied by shock waves which expand throughout the entire eye. In our experiments, we measured the amplitudes of shock waves at the walls of artificial eyes caused by single and multiple pulses of optical energy originating from an Nd:YAG laser at a wavelength of 1.064 micron. We have shown that the effects observed are not caused by mechanical resonance. We believe that similar results can be expected for human eyes. The peak pulse amplitudes in artificial eyes of different length were found to increase linearly as a function of the energy transferred into the eye. The peak amplitudes of pulse sequences were found to be only half of those for single pulses of comparable energy. In laser surgery, such sequences can be preferable if they achieve the same effect.

Energy Transfer↗
PubMed1987

Pressure compliance of the optic nerve head in low tension glaucoma.

Twenty eyes of 10 healthy subjects, 11 eyes of seven patients with low tension glaucoma, and three eyes of three patients with ischaemic optic neuropathy were investigated. Visual evoked responses were recorded under stepwise artificially increased intraocular pressures. The results of the visual evoked response recording (pressure compliance test) allow a clear distinction to be made between healthy subjects, patients with low tension glaucoma, and patients with ischaemic optic neuropathy. In the groups investigated a lack of autoregulation of the optic nerve head circulation was found in patients with low tension glaucoma only. Patients with anterior ischaemic optic neuropathy showed the same pressure compliance behaviour as healthy subjects. The methods used here seem to provide a practicable clinical tool in the differential diagnosis of low tension glaucoma.

Evoked Potentials, Visual↗
PubMed1986

[A test of pressure tolerance of the optic nerve head in ocular hypertension].

VER was recorded in 7 patients with ocular hypertension while intraocular pressure was artificially elevated. Four of the patients manifested signs of vascular autoregulation, while in 3 no such signs were observed. This absence of autoregulation was also observed in primary open-angle glaucoma patients. On the basis of these first results it may be expected that the pressure compliance test will identify patients with ocular hypertension in whom damage to the optic disk is likely to occur at a later date.

Adult↗
PubMed1986

Effect of timolol on optic nerve head autoregulation.

Healthy subjects show, in a special pressure compliance test of the optic nerve head, signs of autoregulation of optic nerve head circulation. In this test visual evoked response (VER) amplitudes were recorded during stepwise increased intraocular pressures. In the resulting VER amplitude/pressure curves glaucoma patients did not show the sign of autoregulation of optic nerve head circulation which is seen in healthy subjects. It is known that topically applied timolol maleate may affect optic nerve head circulation. Therefore the pressure compliance test was performed in 20 healthy eyes before and after 3 days of topically applied timolol maleate 0.5%. The aim of the study was to test the effect of topically applied timolol on optic nerve head autoregulation. In addition we determined the ocular perfusion pressures, heart rate and mean arterial blood pressure. While the ocular perfusion pressures show a slight, but statistically not significant, decrease under timolol, the systemic parameters and the autoregulation behavior did not change.

Adult↗
PubMed1985

Autoregulation of ocular blood flow during changes in intraocular pressure. Preliminary results.

Visual evoked potentials were recorded in six normal subjects and in three patients with primary open-angle glaucoma, while intraocular pressure was artificially elevated in stepwise increases. The resulting perfusion-pressure amplitude curves in our controls showed a kink, which can be interpreted as a sign of vascular autoregulation. No kink was observed in the curves of our glaucoma patients, which we interpret as indicating a lack of vascular autoregulation in primary open-angle glaucoma.

Adult↗
PubMed1982

[Fluorescein angiography of the choroid with elevated intraocular pressure (author's transl)].

Artificially induced increases in intraocular pressure slow the influx of dye during fluorescein angiography sufficiently to permit a sparation in time of the filling of the retina and the choroidea. During the filling of the choroidea segmental filling patterns appear in the form of lobules: the size of these wes determined. Interarterial anastomoses between ciliar arteries were also demonstrated. The clarity of the photographs was enhanced by computer-assisted image evaluation.

Adult↗
PubMed1982

[Fixation in cases of reduced visual acuity (author's transl)].

The authors describe a new device wih a built-in fixation lamp, which enables small children and patients with reduced visual acuity to fix more steadily. The device generates a sequence of flashes for fixation without any risk of triggering photoconvulsive responses.

Adult↗
PubMed1981

[Depiction of chorio-retinal anastomoses with the help of computer-assisted fluorescent angiography (author's transl)].

We recently had the opportunity of evaluating the technique of computer analysis of fundus photography and fluorescein angiograms. Two angiograms were obtained over a period of three months from a patient with senile macular degeneration. At this time we are applying two techniques: black and white photographs with differential contrast enhancement, as well as photographs made with false colours, with and without contrast enhancement. Both of these techniques enables us to confirm the presence of chorio-retinal anastomoses at the site of the macular degeneration. We assume that this was caused by two occlusions of a choroidal venule.

Chorion↗