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M Zehetmayer

Publications and source records attributed to M Zehetmayer.

At least 19 recordsLinked to original sources
PubMed2003

Current percolation and anisotropy in polycrystalline MgB(2).

The influence of anisotropy on the transport current in MgB(2) polycrystalline bulk samples and wires is discussed. A model for the critical current density is proposed, which is based on anisotropic London theory, grain boundary pinning, and percolation theory. The calculated currents agree convincingly with experimental data, and the fit parameters, especially the anisotropy, obtained from percolation theory agree with experiment or theoretical predictions.

Journal Article↗
PubMed2001

A linac-based stereotactic irradiation technique of uveal melanoma.

PURPOSE: To describe a stereotactic irradiation technique for uveal melanomas performed at a linac, based on a non-invasive eye fixation and eye monitoring system. METHODS: For eye immobilization a light source system is integrated in a standard stereotactic mask system in front of the healthy eye: During treatment preparation (computed tomography/magnetic resonance imaging) as well as for treatment delivery, patients are instructed to gaze at the fixation light source. A mini-video camera monitors the pupil center position of the diseased eye. For treatment planning and beam delivery standard stereotactic radiotherapy equipment is used. If the pupil center deviation from a predefined 'zero-position' exceeds 1 mm (for more than 2 s), treatment delivery is interrupted. Between 1996 and 1999 60 patients with uveal melanomas, where (i) tumor height exceeded 7 mm, or (ii) tumor height was more than 3 mm, and the central tumor distance to the optic disc and/or the macula was less than 3 mm, have been treated. A total dose of 60 or 70 Gy has been given in 5 fractions within 10 days. RESULTS: The repositioning accuracy in the mask system is 0.47+/-0.36 mm in rostral-occipital direction, 0.75+/-0.52 mm laterally, and 1.12+/-0.96 mm in vertical direction. An eye movement analysis performed for 23 patients shows a pupil center deviation from the 'zero' position<1 mm in 91% of all cases investigated. In a theoretical analysis, pupil center deviations are correlated with GTV 'movements'. For a pupil center deviation of 1 mm (rotation of the globe of 5 degrees ) the GTV is still encompassed by the 80% isodose in 94%. CONCLUSION: For treatments of uveal melanomas, linac-based stereotactic radiotherapy combined with a non-invasive eye immobilization and monitoring system represents a feasible, accurate and reproducible method. Besides considerable technical requirements, the complexity of the treatment technique demands an interdisciplinary team continuously dedicated to this task.

Eye Movements↗
PubMed2001

Influence of sex, visual acuity, and systemic disease on delayed presentation for cataract surgery in Austria.

PURPOSE: To determine the influence of sex, age, preoperative visual acuity, and systemic disease on the delay in presentation for first-eye cataract surgery. SETTING: University Eye Clinic, Vienna, Austria. METHODS: This retrospective study comprised 200 consecutive patients with age-related cataract who were referred to the Ophthalmology Department of the University of Vienna and who had cataract surgery in the first eye. Patients with additional intraocular procedures or with other ocular comorbidity were excluded. Age, sex, preoperative best corrected Snellen visual acuity in both eyes, ocular and systemic comorbidity, and the duration of preoperative visual deterioration were recorded. The patients were divided into groups depending on systemic comorbidity. The severity of disease was categorized as no therapy necessary or nonexistent, nonsevere, or severe. RESULTS: The mean age of women and men was 74.9 years and 70.7 years, respectively, and the mean preoperative visual acuity, 0.31 and 0.24. The duration of preoperative visual deterioration was 8.6 months and 12.2 months, respectively. All differences were statistically significant (P <.05). The visual acuity in the better eye was not significantly different between men and women. Neither the presence nor the type of systemic disease influenced preoperative visual acuity or the duration of preoperative visual deterioration. CONCLUSIONS: Although the visual acuity in the better eye was not different between men and women, men had cataract surgery after a longer duration of visual deterioration and with a worse visual acuity. More public information about cataract surgery is required to keep visual deterioration secondary to cataract to a minimum.

Adult↗
PubMed2000

Local tumor control and morbidity after one to three fractions of stereotactic external beam irradiation for uveal melanoma.

BACKGROUND AND PURPOSE: To evaluate prospectively local tumor control and morbidity after 1-3 fractions of stereotactic external beam irradiation (SEBI) in patients with uveal melanoma, unsuitable for ruthenium-106 brachytherapy or local resection. MATERIAL AND METHODS: This phase I/II study includes 62 selected patients with uveal melanoma. The mean initial tumor height was 7.8+/-2.8 mm. With the Leskell gamma knife SEBI, 41 patients (66%) were irradiated with two equal fractions of 35, 30 or 25 Gy/fraction, 14 patients (22%) were treated with three fractions of 15 Gy each, and seven patients (11%) with small tumor volumes below 400 mm(3) were treated with one fraction of 45 Gy. The mean total dose was 54+/-8 Gy. The minimal follow-up period was 12 months, and the median follow-up was 28.3 months. Data on radiation-induced side-effects were analyzed with the Cox proportional hazards model for possible risk factors. RESULTS: Local tumor control was achieved in 98% and tumor height reduction in 97%. The mean relative tumor volume reductions were 44, 60 and 72% after 12, 24 and 36 months, respectively. Seven patients developed metastases (11%). Secondary enucleation was performed in eight eyes (13%). Morbidity was significant in tumors exceeding 8 mm in initial height; it was comparable and acceptable in those smaller. In the stepwise multiple Cox model, tumor localization, height and volume, planning target volume (PTV), total dose and patient age were identified as the strongest risk factors for radiation-induced lens opacities, secondary glaucoma, uveitis, eyelash loss and exudative retinal detachment. In this model, the high-dose volume irradiated with more than 10 Gy/fraction was the strongest risk factor for radiation-induced uveitis. CONCLUSIONS: Stereotactic external photon beam irradiation and a total dose of 45-70 Gy delivered in one to three fractions are highly effective at achieving local tumor control in uveal melanoma. Further clinical studies using smaller fraction doses, and consequent smaller high-dose volumes, are justified to optimize dose and fractionation. Fractionated stereotactic irradiation has a challenging potential as an eye-preserving treatment in uveal melanoma.

Adult↗
PubMed2000

High-resolution dose profile studies based on MR imaging with polymer BANG(TM) gels in stereotactic radiation techniques.

High-resolution dose profiles produced by the Leksell Gamma Knife were obtained in BANG(TM) polymer gel, using a 3 T whole-body scanner upgraded by a magnetic resonance microscopy unit. The gel was contained in 22.3 mm diameter flasks that were inserted into a solid, tissue-equivalent head phantom irradiated by fields of by 8 and 14 mm collimators. Dose profiles were obtained from a linear dose-response curve (R(2) vs. Dose). Excellent agreement was obtained when the gel data were compared to film dosimetry and calculated data.

Calibration↗
PubMed2000

Astigmatism correction with a foldable toric intraocular lens in cataract patients.

PURPOSE: To determine the efficacy and rotational stability of a toric posterior chamber silicone intraocular lens (IOL) to correct preoperative astigmatism in cataract patients. SETTING: Department of Ophthalmology, University Hospital of Vienna, Vienna Austria. METHODS: Between 1993 and 1998, foldable toric single-piece plate-haptic silicone IOLs were implanted in 37 eyes (30 patients). The cylindrical IOL power was 2.00 diopters (D) (n = 29), 3.50 D (n = 7), or 4.00 D (n = 1). Phacoemulsification was performed through a scleral or a corneal sutureless self-sealing incision. Outcomes of Snellen visual acuity (without, with spherical, and with best correction), refractive and keratometric astigmatism, and IOL rotation after early postoperative (mean 15.9 days +/- 10.1 [SD]) and long-term (mean 20.3 +/- 16.6 months) follow-ups were evaluated. RESULTS: At last follow-up, 31 eyes (83.8%) had a spherically corrected and 34 (91.9%) a best corrected visual acuity of 0.5 (20/40) or better. Mean preoperative refractive and keratometric astigmatism was 2.68 and 2.70 D, respectively. At the last postoperative follow-up, mean refractive astigmatism was reduced to 0.84 D; keratometric astigmatism was 2.30 D. In 7 eyes (18.9%), the IOL axis was rotated a maximum of 25 degrees. In all 37 eyes, the axis of the toric IOL remained within 30 degrees of rotation. CONCLUSIONS: Early postoperative and long-term follow-ups showed effective and stable correction of astigmatism after implantation of a foldable toric posterior chamber silicone IOL.

Aged↗
PubMed1999

Fractionated stereotactic radiotherapy with linear accelerator for uveal melanoma--preliminary Vienna results.

PURPOSE: To study local tumor control and radiogenic side-effects after fractionated stereotactic radiotherapy for uveal melanoma. PATIENTS AND METHODS: Between June 1997 and February 1998, 21 patients suffering from uveal melanomas have been treated with stereotactic 6 MeV LINAC (Saturne 43, General Electric, France) in conjunction with a stereotactic frame system (BrainLAB, Germany). Immobilization of the eye was ensured with an optical fixation system which was proven reliable. During radiotherapy, movements of the irradiated eye were controlled on a monitor and documented by video recording. All patients co-operated very well with the optical fixation system. In 1164 measurements, the median value of horizontal deviation of the diseased eye during treatment was 0.3 mm (range: 0 to 1.3 mm). Median vertical deviation was 0.2 mm (range: 0 to 1.2 mm). For all patients, mean tumor prominence before treatment was 6.0 +/- 2.2 mm. In 20 patients, the total dose of 70 Gy (at 80%) was delivered in 5 fractions within 10 days. In one patient with a ciliary body tumor, the total dose of 70 Gy was divided into 7 fractions for better sparing of the anterior eye segment. RESULTS: After a follow-up of at least 6 months, local tumor control was seen in all eyes. Mean tumor thickness reduction after 3, 6 and 9 months was 7%, 13% and 31%, respectively. Up to now, only mild subacute side-effects located in the anterior eye segment have been noticed. CONCLUSION: Optical fixation of the eye allows high precision stereotactic radiotherapy with small safety margins. Fractionated stereotactic radiotherapy and 70 Gy total dose delivered in 5 fractions seems to be appropriate for local tumor control in uveal melanoma. Further long-term studies with extended number of patients will be necessary to conclude on the use of linac-based fractionated stereotactic radiotherapy for uveal melanoma.

Austria↗
PubMed1999

Three-year clinical outcome after penetrating keratoplasty for keratoconus with the guided trephine system.

PURPOSE: To determine the long-term clinical outcome after keratoplasty with the guided trephine system in keratoconus eyes. METHODS: In a prospective study, all consecutive cases of penetrating keratoplasty had trephination performed with the guided trephine system, with which both donor and recipient cornea are trephined from the epithelial side with a same-sized blade. For wound closure, a double running antitorque suture technique with 10-0 nylon was used. Uncorrected and best-corrected Snellen visual acuity, subjective refraction, and astigmatism by keratometry were evaluated after final suture removal, 2 and 3 years postoperatively. RESULTS: In the 31 patients (31 eyes) enrolled, mean best-corrected visual acuity improved from 0.72 +/- 0.16 (20/30) after final suture removal to 0.88 +/- 0.15 (20/25) 3 years postoperatively (P < .001). The mean spherical equivalent increased from -0.86 +/- 2.10 diopters after final suture removal to -2.35 +/- 2.65 diopters 3 years postoperatively (P < .001). Mean keratometric astigmatism decreased from 4.68 +/- 1.76 diopters after final suture removal to 3.57 +/- 1.37 diopters 3 years postoperatively (P = .001). Furthermore, an increase in mean keratometric levels with time (P = .01) was observed and associated with myopic shift (r(s) = -.46, P = .008). CONCLUSION: With the guided trephine system, we attained favorable visual results, with prolonged improvement of visual acuity during the entire follow-up period. Our data show low and decreasing degrees of corneal astigmatism over time. During the follow-up period, a myopic shift was found after final suture removal. Nevertheless, this technique of performing same-sized grafts reduces postoperative residual myopia.

Adult↗
PubMed1999

A novel 675.2 nm diode laser densitometer for use with GafChromic films.

In this article we compare the accuracy of a diode laser densitometer emitting 675.2 nm to that of a commercial He-Ne laser densitometer emitting 632.8 nm for GafChromic MD-55 film readout. A Leksell gamma unit (AB Elekta Stockholm, Sweden) Model B with a 14 and 8 mm collimator at the same isocenter (combined 11 mm collimator) was used to irradiate GafChromic MD-55 films. Dose response curves, dose cross profile and FWHM were measured with a custom-designed diode laser scanning device, emitting light at 675.2 nm. The same data were recorded with a commercial He-Ne laser densitometer (PTW FIPS Plus, Freiburg, Germany), emitting light at 632.8 nm. Both measurements were compared to dose cross profiles of a radiosurgery dose planning program (GammaPlan 5.12, Elekta, Sweden). Compared to the commercial He-Ne laser densitometer, the custom-designed diode laser scanning device showed better agreement with the calculated dose cross profile. For two axes, the full width half maxima (FWHM) of the diode laser scanning device was within 0.1 mm deviation compared to the data calculated by the dose planning program. The FWHM of the commercial He-Ne laser densitometer was less accurate (1.6 and 2.1 mm deviation). Our data show that a diode laser scanning device using a light source emitting 675.2 nm increases the accuracy of a GafChromic MD-55 film readout. This greater accuracy may be related to the diode laser measuring the optical density close to maximum absorption of the GafChromic film MD-55 (671-675 nm).

Densitometry↗
PubMed1999

Ocular arterial blood flow of choroidal melanoma eyes before and after stereotactic radiotherapy using Leksell gamma knife: 2 year follow up.

AIMS: To evaluate the effect of high dose stereotactic radiotherapy on the ocular blood flow of patients with uveal melanoma. METHODS: Colour Doppler imaging (CDI) was used to measure blood flow velocity and vascular resistance in the ophthalmic, short posterior, and central retinal arteries of nine patients suffering from uveal melanoma. The measurements were taken before, 6 months, 1 year, and 2 years after stereotactic radiotherapy. Irradiation was performed with the Leksell gamma knife with the 59 (41-66.5) Gy total marginal dose divided in two equal fractions. CDI results were compared with age and sex matched healthy control eyes. RESULTS: At each time of measurement, blood flow velocity in the central retinal artery of the affected eyes was significantly reduced whereas vascular resistance was only increased at the 2 year follow up. Blood flow velocity and vascular resistance in the short posterior arteries of melanoma eyes were also only significantly altered at the 2 year follow up. Blood flow velocity and vascular resistance in the ophthalmic artery of melanoma eyes were not changed at all follow ups. CONCLUSIONS: In the melanoma eyes, blood flow velocity in the central retinal artery is reduced. High dose stereotactic radiotherapy with the Leksell gamma knife and a 59 (41-66.5) Gy total marginal dose in two fractions leads to a significant reduction of blood flow and a significant increase in resistance variables in the small ocular arteries within 2 years.

Adult↗
PubMed1999

[Idiopathic sclero-choroid calcification].

BACKGROUND: Idiopathic sclerochoroidal calcification (ISC) is an unusual, benign disorder occurring at the level of the posterior choroidea and sclera. Clinical differential diagnosis includes choroidal osteoma, choroidal metastasis, choroidal melanoma, choroidal amelanotic naevus and choroiditis. PATIENT: A 61-year old man was referred with the diagnosis of multifocal choroidal tumor in both eyes. Fundoscopy showed bilateral yellow lesions located near the superotemporal arcade. RESULTS: Fluorescein angiography shows the late staining of the choroidal lesions. Ultrasonographically highly reflective lesions (sclerochoroidal placoid lesions at the sclero-choroidal interface in the CT) confirms the clinical diagnosis. The serum calcium and phosphate metabolism is normal. CONCLUSION: The Idiopathic Sclerochoroidal Calcification (ISC) is a rare echographical differential diagnosis to the choroidal osteoma. ISC is a heterotopic calcification of the posterior pole in both eyes, usually located near the superotemporal arcade.

Calcinosis↗
PubMed1998

Ophthalmic and genetic screening in pedigrees with familial adenomatous polyposis.

PURPOSE: To study the possible association between ophthalmic findings, genetic status, and clinical course of the disease in Austrian pedigrees with familial adenomatous polyposis (FAP). METHODS: Thirty-nine members of 16 consecutive FAP families with 20 affected patients and 19 relatives with a 50% a priori risk to develop the disease were examined ophthalmologically. The intestinal status of all persons was established by colonoscopy. Direct or indirect molecular genetic analysis, or both, was possible in eight of the 16 FAP families. RESULTS: Congenital hypertrophy of the retinal pigment epithelium (CHRPE) was discovered in 15 (75%) of the 20 persons affected by familial adenomatous polyposis. Five (25%) of the patients with an established FAP were CHRPE-negative. Four of the 19 at-risk individuals were CHRPE-positive. According to DNA analysis, five of the 19 at-risk relatives had a high risk to develop a manifest disease. The ophthalmoscopic tests were in complete agreement with the molecular risk estimation. Furthermore, the combined results of endoscopy and ophthalmoscopy suggested a relationship between a positive CHRPE status and the severity of FAP. CONCLUSIONS: Ophthalmic examinations facilitate predictive diagnosis in FAP patients and first-degree relatives, permitting a noninvasive, highly reliable risk assessment. When present, CHRPE lesions are a reliable clinical marker for FAP in CHRPE-positive families. In CHRPE negative families, negative ophthalmic examinations are of no predictive value. The CHRPE status can add information about the location of the genetic mutation. The combination of an ophthalmic examination with DNA analysis and endoscopy improves the risk assessment of FAP carriers.

Adenomatous Polyposis Coli↗
PubMed1998

Corneal flap incision technique for sutureless cataract surgery.

A self-sealing incision technique for cataract surgery has been developed. It is appropriate for implantation of rigid-optic intraocular lenses (IOLs) up to 7.0 mm. The incision is designed to meet the principle criteria of sutureless cataract surgery, such as optimal instrument handling, easy IOL implantation, and minimal postoperative patient care.

Cataract Extraction↗
PubMed1998

Ultrastructure of clear corneal incisions. Part I: Effect of keratomes and incision width on corneal trauma after lens implantation.

PURPOSE: To examine the ultrastructure of clear corneal incisions (CCIs) performed with diamond keratomes and steel blades as well as the corneal trauma after implantation of a foldable intraocular lens (IOL) through two incision widths. SETTING: University Eye Clinic and Institute of Histology and Embryology II, University of Vienna, Austria. METHODS: Twenty-four human cadaver eyes without prior ocular surgery were obtained from the University Eye Bank, Vienna. Single-plane CCIs were performed with 3.0 and 3.2 mm Alcon steel blades and with a 3.0 mm Huco diamond keratome. The AMO PhacoFlex II lens was implanted with a Fine II folder. During the entire procedure, the eye pressure was kept between 26 and 30 mm Hg by infusing balanced salt solution into the anterior chamber. Specimens were prepared for light microscopy, transmission electron microscopy, and scanning electron microscopy according to standard procedures. RESULTS: The diamond keratome produced cleaner cuts than the steel blade. After IOL implantation, 3.0 mm steel blade incisions exhibited extensions at their lateral ends. Within these extensions, the collagen lamellae were displaced and torn. This was not true with 3.2 mm tunnels. Because of the thickness of a 3.0 mm diamond keratome, the extent of corneal trauma was between that found with 3.0 and 3.2 mm steel keratome tunnels. CONCLUSIONS: Implantation of the SI-30 through 3.0 mm CCIs produced by the steel blade led to more severe corneal trauma than implantation through 3.2 mm steel blade incisions or 3.0 mm diamond keratome incisions. Thus, IOL implantation through incisions that are too small intensifies corneal trauma.

Aged↗
PubMed1998

Ultrastructure of clear corneal incisions. Part II: Corneal trauma after lens implantation with the Microstaar injector system.

PURPOSE: To examine the ultrastructure of clear corneal incisions (CCIs) after implantation of a plate-hepatic intraocular lens (IOL) with the Microstaar injector system through two incision widths. SETTING: University Eye Clinic and Institute of Histology and Embryology II, University of Vienna, Austria. METHODS: Fourteen human cadaver eyes without prior ocular surgery were obtained from the University Eye Bank, Vienna. Single-plane CCIs were performed with 3.0 and 3.2 mm steel keratomes. Using the Microstaar injector system, a foldable silicone plate-haptic IOL (23 diopters) was implanted in the anterior chamber. During the entire procedure, the eye pressure was kept between 26 and 30 mm Hg by infusing balanced salt solution into the anterior chamber. Specimens for light microscopy and scanning electron microscopy were prepared according to standard procedures. RESULTS: After IOL implantation, the 3.0 mm steel blade incisions exhibited distinct distensions at their lateral ends. Adjacent to these distensions, the collagen lamellae were pressed apart, displaced, and torn. In 3.2 mm tunnels, the corneal trauma at both lateral ends was considerably less severe. These incisions also showed a better primary adaptation of the wound lips after implantations. CONCLUSIONS: Implantation performed with the Microstaar injector system through 3.0 mm steel blade CCIs led to considerably more severe corneal trauma than implantation through 3.2 mm incisions.

Aged↗
PubMed1998

Shuttle dose at the Vienna Leksell Gamma Knife.

The aim of this study was to determine the shuttle dose for all collimator helmets (4, 8, 14 and 18 mm) of the Gamma Knife, model B, in Vienna, Austria. The additional dose accumulated during the transport of the patient in and out of the treatment position should be considered in the dose planning procedure of multicentre treatment regimens and in fractionated stereotactic Gamma Knife radiotherapy. The GafChromic film study was basically used to determine the shuttle dose of all four collimator helmets. In addition, measurements with an ionization chamber (18 and 14 mm collimator--and, for the 18 mm collimator helmet, TLD dosimetry--were performed in order to confirm the GafChromic film data. The shuttle dose ranged between 99.6 and 183.5 mGy, depending mainly on the size of the collimator and the irradiated isocentres at the half-life activity of Co-60 in a brand new Gamma unit. Our film-generated data were in good correlation with the dose levels obtained with the ionization chamber and the TLD dosimetry, showing a dose difference of less than 0.8%. Since it was possible to verify the shuttle dose even for the 4 and 8 mm collimator helmets, we consider it a non-negligible factor and would advocate the inclusion of the shuttle dose in radiosurgical dose planning.

Biophysical Phenomena↗
PubMed1998

Interlacing and cross-angle distribution of collagen lamellae in the human cornea.

PURPOSE: The interlacing and cross angles between the collagen lamellae within the human corneal stroma were studied by means of scanning electron microscopy (SEM). METHODS: For SEM, cells and noncollagenous extracellular matrix were removed with 10% sodium hydroxide. Transmission electron microscopy (TEM) preparations were performed according to standard procedures. The interlacing of lamellae was studied within the limbal, paracentral, and central regions of five different layers. The cross angles between the longitudinal axes of adjacent lamellae were measured. The distribution of these angles within defined layers and regions was compared. Special attention was paid to the interlacing of the lamellae. RESULTS: Lamellae split in an anteroposterior direction as well as horizontally into branches and are interlaced by crossing the fissures between the branches. Smaller lamellae cross through clefts of neighboring lamellae. The cross angles show a high variability of 1 degree - 90 degrees. With the exception of the limbal region of the layer adjacent to Descemet's membrane, the distribution of cross angles is similar. A frequent occurrence of cross angles <30 degrees (68%) in this limbal layer can be explained by a pseudocircular orientation (ligamentum circulare corneae) of the lamellae. CONCLUSION: The present study shows that the three-dimensional organization of the collagen lamellae is characterized by a greater extent of lamellar interlacing than has been assumed until now.

Adult↗