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Biomedical subjects

R Guthoff

Publications and source records attributed to R Guthoff.

At least 109 records · Page 6Linked to original sources
PubMed1990

Measurement of elastic resisting forces of intraocular haptic loops of varying geometrical designs and material composition.

The relationship between experimentally induced intraocular lens (IOL) haptic deformation and resulting elastic haptic counter-resisting forces measured by electronic dynamometry was examined for 34 different IOL haptics of varying material composition and geometrical designs. Poly(methyl methacrylate) (PMMA) and polypropylene loops of similar geometry did not fundamentally differ from one another, although lenses of differing geometry behaved differently. Unlike PMMA and polypropylene loops, soft haptics of poly-HEMA and silicone rubber demonstrated a larger elastic resistance force to the same degree of deformation. This was based upon design characteristics of the lenses and not upon intrinsic properties of the materials, which would have produced the opposite result. By comparative analysis of these dynamometer measurements and considerations of the lens design and elastic properties (including memory) of the component materials, we can calculate the stresses upon the zonular and capsular bag structures during and after IOL implantation.

Biocompatible Materials↗
PubMed1990

[Magnetic resonance tomographic diagnosis of retrobulbar neuritis using inversion recovery sequences].

Inversion recovery sequences with short inversion periods (STIR sequences) are particularly suitable for the examination of the intra-orbital and intracanalicular portion of the optic nerve, since they selectively suppress interference from neighbouring fat. This technique makes possible direct demonstration of retrobulbar neuritis that had to be diagnosed exclusively by clinical criteria up to now. As evidence of inflammatory changes in 15 out of 18 patients with acute retrobulbar neuritis, there were areas of increased signal intensity in the affected nerve; in six cases the nerve was also swollen. In eight normals and five patients with healed retrobulbar neuritis, the signal and calibre of the optic nerves were normal.

Adult↗
PubMed1990

[The regression behavior of choroid melanoma following radiotherapy--a new prognostic parameter?].

The present paper reports on follow-up examinations of 246 patients after Ruthenium106 treatment of choroidal melanomas (follow-up time 1.8 to 13 years). In January 1988, 212 patients were alive and free of metastases; 15 had died, 12 of them of melanoma metastases, and 17 could not be followed up. In a retrospective analysis of factors influencing tumor-related mortality, the rate of regression of irradiated tumors was found to be particularly significant. The mean time taken to reduce tumor volume by half was 4.4 months in patients who died of metastases, as against 6.6 months in a matched group of survivors. Using discriminance analysis, the difference was found to be highly significant (P = 0.0058). In the total patient population, a significant correlation was found between pretreatment tumor volume and the probability of metastases (P = 0.058). It may be concluded, though with the qualification that the number of tumor-related deaths was small, that the tumor regression rate is an important factor in the prognosis for patients with Ruthenium-treated malignant choroidal melanomas.

Choroid↗
PubMed1990

[Flexibility of intraocular lens haptics of various geometry and materials].

The relations between the deformation and resulting resilience of lens haptics with various geometries and made of different materials were studied. While there are no fundamental differences between PMMA and PP haptics with identical geometries, the resilience of soft lenses made of poly-HEMA and silicone rubber subjected to the same deformation is significantly higher. On the basis of such measurements it is possible to estimate stress on the capsular bag during and after implantation. In light of recent publications concerning the prevention of secondary cataract, permanent circular tensioning of the lens capsule appears a desirable goal. This requirement is best satisfied with a material with permanently high elasticity, which tensions the equator of the capsular bag over 360 degrees.

Acrylates↗
PubMed1989

[Doppler sonographic findings in intraocular tumors].

B-scan-ultrasonography combined with Doppler measuring facilities (DUPLEX technology) was applied in 31 patients with intraocular tumors (27 choroidal melanomas, 4 cavernous hemangiomas of the chorioid). In all but 2 patients, Doppler frequency shift was observed inside the tumor, which was interpreted as being caused by high-velocity blood flow (maximum 10 cm/s). After conservative treatment (beta irradiation with ruthenium 106) the Doppler signals decreased in height in some patients. After 6-8 months, no frequency shift could be determined. Choroidal hemangiomas showed similar signal behavior, so that differential diagnosis by means of Doppler analyses does not seem to be possible.

Aged↗
PubMed1989

[Doppler sonographic findings in the central retinal artery and vein].

In a group of healthy subjects of varying ages, the flow velocities in the central retinal artery and vein were measured with a B-mode-guided pulsed duplex scanner. The first measurements were taken in the unaffected eye. The maximal systolic flow velocities ranged from 2.9 to 10 cm/s (mean 5.7 cm/s) in the central vein and from 4 to 20 cm/s (mean 9.5 cm/s) in the central artery. The correct assignment of the measuring points in the papillary region was verified by the close correlation between the flow velocity and artificially elevated intraocular pressure. After evaluating 158 clinical examinations, we try to outline the diagnostic possibilities of the method with respect to single observations in patients with ocular circulatory disturbances.

Blood Flow Velocity↗
PubMed1989

[Magnetic resonance tomography in ophthalmologic diagnosis].

First introduced into clinical use in 1981 as an investigative modality, this technique offers a wealth of information about the topography and physicochemical composition of the soft tissues in the orbit and central nervous system. However, to date, some of this information is still not incompletely understood. This method can be used to augment the usual diagnosis methods in selected cases of intraocular tumor. It is possible to differente between Coats disease and non-calcified retinoblastoma, and the paramagnetic properties of melanin allow the melanin content of choroidal tumors to be estimated. However, so far magnetic resonance tomography (MRT) still cannot, be recommended as a routine diagnostic procedure. MRT is of significant help in localizing pathological processes involving the orbital apex. The optic nerve and its surrounding dural sheath can be imaged with consistent reliability as distinctly separate structures. In cases of retrobulbar optic neuritis, the increase in signals by the pathologically involved segments of the optic nerve permits these segments to be differentiated from the adjacent optic nervous tissue that is unaffected. After administration of paramagnetic contrast material, the sinus cavernosus region can be visualized particularly well. Inflammatory and thrombotic processes can be diagnosed better than with the methods previously available. Surgery can be planned more easily in cases of intracranial space-occupying lesions, especially in the region of the chiasmic portion of the optic nerve; thus at present MRT can be viewed as the method of choice in planning the operative treatment of such lesions.

Diagnosis, Differential↗
PubMed1989

[New diagnostic approaches in the assessment of the enlarged optic nerve--comparison of ultrasound echography and magnetic resonance tomography].

Enlargement of the orbital optic nerve was examined in patients by means of A- and B-scan ultrasonography and NMR imaging techniques; the results were then compared. We found that separation of the optical nerve sheets and the nerve structures themselves can be demonstrated with both methods, and increased width of the subarachnoidal space can be differentiated from the axonal cylinder. Our findings in meningeomas and gliomas are analyzed, as are the various reasons for edema of the disc. The pathogenesis of fluid collection in the subarachnoidal space in tumors of the optic nerve is discussed.

Diagnosis, Differential↗
PubMed1988

Ophthalmoscopic findings in spontaneous carotid cavernous fistula: an analysis of 20 patients.

The pathophysiological influence of spontaneous carotid cavernous fistula (CCF) on retinal/orbital circulation is discussed. Of 20 patients, 1 case of papilloedema, 4 of choroidal detachment (CD), 2 of exudative retinal detachment (ERD) and 3 cases of central venous thrombosis (CVT) were seen, associations that on rarely reported in the literature. An elevation in the episcleral venous pressure was measured that was more than twice the normal, which explains the ophthalmoscopic findings.

Aged↗
PubMed1988

[Dacryocystography--conventional technic or digital subtraction technic?].

The lacrimal drainage systems of 92 patients were examined by a digital subtraction technique; 30 patients were examined additionally by a conventional technique, using films obtained during screening for the contrast injection. The digital subtraction dacryocystogram provided excellent demonstration of the lacrymal sac and of the tear ducts, but there is little diagnostic gain when compared with the conventional technique. Both methods are highly reliable. In view of its low radiation dose and rapid and simple course, conventional dacryocystography is regarded as the method of choice for routine examinations. The digital subtraction technique should be reserved for special problems.

Adolescent↗
PubMed1988

[Role of nuclear magnetic resonance imaging in the diagnosis of monosymptomatic optic neuritis].

34 patients with monosymptomatic optic neuritis were examined ophthalmologically and by magnetic resonance imaging (MRI). In 18 patients subclinical lesions with a high MRI signal intensity were found. The distribution of these lesions was similar to that seen in multiple sclerosis. Neither the severity of the visual impairment nor the course of remission correlated to the MRI findings. Pathologic MRI findings were more common in patients aged over 27 than in younger patients (57% vs. 42%).

Adolescent↗
PubMed1988

[Aeromonas hydrophila dacryocystitis. Case report].

The present paper reports on a case of severe dacryocystitis with a dacryolith, caused by Aeromonas hydrophila. On the basis of this case the authors show that a therapy effective in vitro does not lead to elimination of bacteria in all cases, so that further therapeutic considerations are necessary.

Abscess↗
PubMed1988

[Ocular myositis--morphology and function--long-term studies of 15 patients].

Findings in 15 patients were analyzed with regard to history, accompanying motility disorders, and clinical course. In two cases histologic findings were also available. A comparison of echographic and CT examinations of the muscles affected and the resulting motility disorders showed that in eight of the 15 patients reduced elasticity of the muscle was practically the only pathologic finding. A significant loss of contractility was found in only four patients. These findings are discussed with reference to the electromyographic findings reported in the literature and the results of the authors' own histologic studies.

Adult↗
PubMed1988

[The role of episcleral venous pressure in the development of secondary glaucomas].

Between 1983 and 1987 the authors studied 64 patients with dilated episcleral vessels and open-angle glaucoma. Elevated episcleral venous pressure was found to be the cause of the increased intraocular pressure. Clinically, the cause of elevation of venous pressure included spontaneous carotid cavernous fistulas, Sturge-Weber syndrome, orbital tumors, endocrine exophthalmos, anterior scleritis and idiopathic cases. A variety of pathophysiological mechanisms causing elevated episcleral venous pressure were found. The clinical course and complications associated with elevated episcleral venous pressure are discussed.

Arteriovenous Fistula↗
PubMed1987

Ultrasonographic measurement of the posterior coats of the eye and their relation to axial length.

In 159 eyes with a spherical correction varying from +14.0 to -27.0 diopters, the axial length and thickness of posterior ocular coats were measured ultrasonographically. As proven in experimental studies, retina, choroid, and sclera were resolved in a considerable percentage of cases by combining A- and B-mode techniques of modern ultrasonographic equipment. The presumed close inverse correlation between the axial length of the eye and ocular coat dimensions was confirmed by statistical analysis. These values were used to calculate the approximative volume of the posterior half of the ocular coats. There was evidence for a constant tissue volume regardless of the difference in surface and axial length parameters between hyperopic and myopic eyes. Results are discussed and compared with theories of axial growth under physiological and pathological conditions.

Animals↗