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Biomedical subjects

B Rassow

Publications and source records attributed to B Rassow.

At least 37 records · Page 2Linked to original sources
PubMed1985

A new laser interferometer for the stimulation of pattern-reversal visual evoked potentials.

A laser interferometer for visual-evoked-potential (VEP) stimulation that allows a rapid pattern reversal in less than 0.5 ms and a continuous variation of the spatial frequency of the pattern is described. The interferometer is applied for the assessment of objective visual acuity. The Fourier transform of the VEP response to the rapid pattern reversal shows an extremely small bandwidth.

Evoked Potentials, Visual↗
PubMed1984

Binocular micromovement recording of human eyes:--methods.

An apparatus is described for binocular recording of micromovements of human eyes, with the contact lens mirror technique used frequently. Horizontal and vertical micromovements of both eyes are recorded simultaneously by means of instruments measuring light-spot positions. Spatial resolution of the measuring instrument is 12 s of arc, while the time resolution is 0.5 ms for this apparatus. The fixation mark (Snellen character) is at a distance of 5 m without any restrictions to the view. The micromovement data are registered by a microcomputer. A second computer enables precise calculation of the results which are given as multicoloured graphs (X/Y-, X/t-graph, velocity/t-graph, frequency analysis, phase correlation of both eyes). In this way the requirements are met for the clinical application of this measuring instrument on patients.

Contact Lenses↗
PubMed1981

[The strength of retinal sear tissue after argon-, xenon-, and cryocoagulation (author's transl)].

A method is presented for measuring the adhesive force between retina and pigment epithelium in rabbit eye preparations. This force shows a great interindividual variation and so the absolute value is of little interest. The variation of several readings in one animal is, however, significantly smaller. Therefore the relative change in adhesive force between untreated and treated areas of one animal can be used. The data shows similar increases of +25-30%. For laser-, xenon-, and cryocoagulation, the maximum adhesive strength is reached within 4-8 days after treatment. After a few weeks the additional adhesion in treated areas slowly fell to about +10% as compared to pretreatment levels.

Adhesiveness↗
PubMed1981

Neural contrast sensitivity measurements with a laser interference system for clinical and screening application.

A He-Ne laser interference device for clinical measurements of the neural contrast sensitivity fraction (CSF) is described. The system uses planoparallel glass plates for the generation of sinusoidal gratings on the retina. Incoherent light from two light-emitting diodes is superimposed for reducing the contrast to a range from 2 X 10-3 to 0.5. The device is coupled with a microcomputer that calculates the contrast sensitivity (CS) and permits control of the system by a dialogue program. The mean CSF for normal observers (95 eyes) is presented, and the data are compared with overall CS values from other authors. Pathologic CSFs of three patients are shown as examples for the clinical application. For screening purposes the CS values for five spatial frequencies are compared with the normal CSF. And loss-of-contrast values are calculated.

Equipment Safety↗
PubMed1980

[Importance of orientation on visual and neuronal resolution (author's transl)].

Spatial resolution of gratings of different orientation has been evaluated in 39 patients, by means of projected slides and by laser interference fringes. Both methods reveal a significantly higher resolution (about 12%) for vertical or horizontal bars compared to oblique ones. The similarity of findings for both methods is indicative of the neuronal origin of this orientation-dependent effect and exclude an optical origin.

Adolescent↗
PubMed1979

[Optical properties and clinical performance of the Topcon retinal camera TRC-FET 3 (author's transl)].

A Topcon Retinal Camera TRC-FET 3 was tested for several weeks under laboratory and clinical routine conditions. The optical properties turned out as good and meet the requirements for retinal cameras in all details. Remarkable is the high speed of the imaging system, which allows working with low flash energies and with high flash frequency. The resolving power is high (8 microns at the center) and decreases slowly to the periphery. The illumination of the fundus is fairly homogeneous. Many filters of good performance are provided. There was no problem in handling the camera, and the test photographs as well as the clinical routine photographs were of high quality.

Clinical Trials as Topic↗
PubMed1978

[Laser lesions of the anterior segment of the rabbit eye. Studies of cornea, iris, lens and sclera using an argon, ruby and YAG-laser].

The anterior segment of the eye of 100 rabbits was exposed to radiation from Argon, Ruby and YAG lasers. The healing process of liminal and supraliminal lesions was evaluated histologically. The iris is the most sensitive tissue for all three lasers (threshold radiant exposure, Argon: 0.004 kJ/cm2, Ruby: 0.01 kJ/cm2, YAG: 0.05 kJ/cm2). Higher energies necessary for lesions in the transparent media were available only with the Argon and YAG lasers. The Argon laser failed to produce lesions in the lens, and threshold radiant exposure for the central cornea was 8 kJ/cm2. The thresholds for YAG lasers lesions in the central cornea and lens were of the same magnitude. The marked absorption of energy by the iris may lead to an accumulation of heat, resulting in lesions of adjacent tissues or a reduction of threshold for those lesions: The threshold in the peripheral cornea was ten times lower than in the center with the Argon laser, four times lower for the YAG laser. The thresholds for Argon and YAG laser lesions in the peripheral sclera lay between the thresholds for the iris and for the peripheral cornea. A safety standard for the anterior segment of the eye should be based on the lowest threshold (Argon laser lesion of the iris). The application of a factor 100 results in a maximal permissible exposure of 40 mJ/cm2. The influence of the beam diameter could not be evaluated.

Animals↗
PubMed1978

[Electron microscopic observations on the effect of laser beams on the retina of the rabbit (author's transl)].

After laser irradations, retinas of 13 rabbits were examined by electron microscope. The laser focus was set between 30 min and 140 h or 6 weeks in advance. The anatomical separation between the retina and the connective tissue of the choriocapillary in all the lesions is preserved by an intact Bruch's membrane. Destruction of the pigment epithelium, rod layer, and outer granular layer occurs in the early stages after coagulation. Later the nuclei of the rods show various stages of degeneration with simultaneous increases in the volume of the Müller's cells. The cytoplasma of the Müller's cells penetrates the nuclei of the sensory cells undergoing degeneration. Proliferation of the pigment epithelium begins after about 20 h. The first appearance of macrophages in the retina is visible after 30 h. Between 92 and 140 h in the area of the pigment epithelium, variously differentiated cells, which partly contain pigment granules and lamellary inclusion bodies, form. Some cells or cell groups which are visible might represent histiocytes within the Bruch's membrane 35, 45, 68, and 92 h as well as 6 weeks after coagulation. They partly cross the outer layer of the Bruch's membrane and neighboring connective tissue of the choroid. According to our studies, pigment epithelial cells, choroidal histiocytes, and Müller's cells participate in the phagocytosis.

Animals↗
PubMed1977

[Lesions of the rabbit cornea produced by laser light (author's transl)].

Threshold radiant exposure of the cornea of gray rabbits was evaluated for Argon- and YAG-Laser light. Threshold for the Argonlaser is about 15 kJ/cm2 (exposure time 200 ms to 2 s, spot size 65 micron). For experimental and methodical reasons the value for the YAG-Laser (115 kJ/cm2) is of limited accuracy. The healing process of supraliminal lesions of the cornea is observed clinically and histologycally up to six weeks following exposure to laser radiation.

Animals↗
PubMed1977

[The prognostic value of the laser-interference-fringe-test with cataract patients (author's transl)].

The retinal visual acuity of 198 cataractous eyes was tested with interference-fringes and compared with the post-operative visual acuity. A new method of creating interference-fringes was used. The interference-fringe technique showed its special clinical value with immature cataracts. It is of certain value also with premature cataracts. With mature and hypermature cataracts no results of clinical value could be obtained. The method seems to have its value with congenital and juvenile cataracts.

Cataract↗
PubMed1977

[Testing of the "retinal acuity" with the laser interference apparatus as a routine clinical method].

The retinal function may be tested by laser-interference-fringes formed on the retina independently of the refraction status of the eye. The perception of these fringes is a subjective test for the retinal function even in case of moderate opacities of the optical media. Experiences with a new apparatus described here showed that the determination of this "retinal acuity" is very simple to perform. The comparison of retinal acuity and visula acuity of several hundred cataratous eyes and the measurement before and after cataract extraction in about 100 cases are discussed. The method gives useful prognostic and diagnostic information to the ophthalmologist.

Cataract↗
PubMed1976

[The astigmatism bioblique. II. Mathematical description (author's transl)].

Optical surface showing an astigmatism bioblique could only approximately be described by mathematical formulas. The best approximation is that one which shows a close relation between regular and bioblique astigmatism. It allows the calculation of the best correcting cylinder, which brings the anavoidable residual astigmatism to a minimum.

Astigmatism↗
PubMed1976

[Laser trabeculopuncture. II. Screen electron mascroscopic findings].

Laser trabeculopuncture was performed on preparations of human anterior chamber angle obtained from cadaver eyes. It was possible repeatedly to make about 50 mum large openings leading from anterior chamber to Schlemm canal. It was necessary to use short exposure times of maximum 200 msec and laser efficiency of at least 1,500 mW at the origin. The results were studied with a scanning electron microscope.

Humans↗