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M Zehetmayer

Publications and source records attributed to M Zehetmayer.

At least 37 records · Page 2Linked to original sources
PubMed1998

Altered organization of collagen in the apex of keratoconus corneas.

PURPOSE: In 15 keratoconus corneas, the three-dimensional arrangement of collagen lamellae was investigated by means of scanning electron microscopy. METHODS: Keratoconus corneas without visible scars were obtained during perforating keratoplasty. The noncollagenous matrix of the stroma was removed with sodium hydroxide. Descemet's membrane was removed mechanically and deeper layers of the stroma were exposed by cutting the tissue tangentially to the corneal surface with an ultramicrotome. The apical and the para-apical regions of keratoconus were compared the central regions of normal corneas. RESULTS: In the apical regions of 11 out of the 15 keratoconus corneas (73%), the arrangement of the collagen lamellae differs from those of the para-apical regions and normal corneas. Their collagen fibrils from uniform layers and no delimited collagen lamellae can be differentiated. Interlacing between adjacent layers in extremely decreased or even absent. In the para-apical region of keratoconus corneas the three-dimensional arrangement of collagen lamellae does not differ from that in normal corneas. CONCLUSION: Stromal thinning and conical ectasia in the apex of keratoconus corneas alters the organization of collagen. This will certainly affect the biomechanical properties of the cornea and further lead to a progression of keratoconus irrespective of its primary pathogenesis.

Adolescent↗
PubMed1998

Radio-opaque markers for stereotactic imaging of uveal melanoma.

In in vitro and in vivo studies, episclerally sutured radio-opaque markers were evaluated as localizers for better determination of the clinical tumour volume prior to stereotactic radio-therapy of uveal melanoma. Four different types of markers were studied in vitro: tantalum marker, 2.5 mm in diameter; ring-shaped markers custom-designed in polymethyl methacrylate (PMMA), 2.6 mm and 3.0 mm in diameter; and barium-impregnated silicone rubber spheres, 2 mm in diameter. In vivo PMMA markers 3.0 mm in diameter and barium-impregnated silicone rubber spheres 2 mm in diameter were used. The best results were obtained with the barium-impregnated silicone rubber spheres both in vitro and in vivo. For the CT-delineation of selected uveal melanomas with either a flat discoid shape or flat tumour extensions or when adjacent serous retinal detachment is present, small episclerally sutured barium-impregnated silicone rubber spheres are useful as localizers for determining the clinical tumour volume.

Humans↗
PubMed1997

Topical anesthesia with pH-adjusted versus standard lidocaine 4% for clear corneal cataract surgery.

PURPOSE: To evaluate and compare the efficacy of a sodium-bicarbonate-adjusted preparation of lidocaine 4% (pH = 7.2) and standard lidocaine (pH = 5.2) for topical anesthesia in clear corneal cataract surgery. SETTING: Department of Ophthalmology, University of Vienna, Austria. METHODS: In a prospective, randomized, double-blind clinical trial, clear corneal cataract surgery was performed under topical anesthesia in 44 eyes of 34 patients. In 22 eyes, pH-adjusted lidocaine 4% was administered; in the other 22, standard lidocaine 4%. Aqueous and serum concentrations of lidocaine were measured by high-performance liquid chromatography and ultraviolet detection. Subjective pain was assessed using a visual analog scale of no pain (0%) to worst imaginable pain (100%). On the first postoperative day, visual acuity, intraocular pressure, and corneal staining with fluorescein were examined. RESULTS: In the pH-adjusted lidocaine group, significantly higher lidocaine concentrations were found in the aqueous humor (15.06 microg/mL +/- 8.2 [SD] versus 4.75 +/- 3.5 microg/mL; P < .0001). In all samples (n = 8), serum lidocaine concentrations were below a minimum detectable level of 0.02 microg/mL. Subjective pain ratings were similar in the pH-adjusted and standard lidocaine groups (mean 9.73 +/- 10.4% and 10.0 +/- 15.4%, respectively). There was no significant between-group difference in intraoperative and postoperative outcomes. CONCLUSIONS: In this study, pH-adjusted lidocaine 4% was a safe, effective topical anesthetic for clear corneal surgery and had minimal local and systemic toxicity. Administration of pH-adjusted lidocaine 4% resulted in significantly higher aqueous humor lidocaine concentrations than administration of standard lidocaine 4%.

Administration, Topical↗
PubMed1997

Dosimetry studies with TLDs for stereotactic radiation techniques for intraocular tumours.

Between March 1993 and January 1997, stereotactic radiation techniques were used to irradiate 66 intraocular tumour patients with the Gamma Knife (Leksell Gamma Knife, model B unit) at the University of Vienna, Austria. This study investigates the dosimetry for stereotactic irradiation of ocular structures. For the dosimetry program KULA 4.4, Gamma Knife stereotactic irradiation of the eye represents an extreme frontal skull position. In addition, irradiation of the eye may be performed in the usual supine position in exceptional cases only. With the patient in the prone position, the dose planning program has to calculate with a significantly large number of single-beam extrapolations. In our first experiment we measured the isocentre dose for eight different gamma-angle positions, both in prone and supine positions, using TLD measurements in an Alderson head phantom. We found a maximum deviation of +/- 1.6% using these individually calibrated TLDs. In the second experiment we examined the dose cross profiles for the two most frequently used treatment positions (supine position, gamma = 65 degrees, and prone position, gamma = 140 degrees). For this purpose we implanted a specially designed TLD array into the orbit of a human cadaver head. We found excellent agreement of the dose values measured for the isocentre as well as the posterior part of the eye with orbit with deviations of less than -2.7%. However, for the anterior part of the eye, deviations between computer-generated calculations and the TLD measurements were found to range up to -30%. These differences were noticed both for supine and prone positions. For the Gamma Knife stereotactic irradiation of ocular tumours or pathologies, precautions should be taken to avoid significant underdosage in the anterior part of the radiation field.

Biophysical Phenomena↗
PubMed1996

Screening by genomic linkage studies and mutation analysis of hereditary adenomatous polyposis coli: usefulness for clinical practice.

A heterogeneous group of patients suffering from adenomatous polyposis coli (APC) were evaluated by clinical and genetic investigations for the first time in Austria. The patients belonged to eight unrelated APC families. In six families several family members were affected with APC, and linkage analysis with highly informative markers was used to estimate the risk of single individuals in these families to develop APC. All index patients were also tested for the most frequent mutation in the APC gene (mutation cluster region, exon 15). Clinical investigations included ophthalmologic tests for congenital hypertrophy of retinal pigment epithelium and colonoscopy. According to DNA analysis, 5 of 19 at-risk individuals had to be considered to be at high risk of having inherited the disease. Four of them underwent proctocolectomy, one patient at risk is under colonoscopic surveillance. The predictive value of indirect genotype analyses reached 83.3%; direct mutation analyses allowed risk estimation in 50% of cases. Ophthalmologic investigation was informative in 75% of the families. Direct and indirect genotyping using a panel of highly polymorphic, closely linked microsatellite markers is a valuable, rapid, reliable method for establishing a presymptomatic diagnosis of APC, especially in families in which more than one affected individual is available for analysis. With regard to the onset of APC and extracolonic manifestations, the variability of APC demands clinical investigations in addition to the molecular tests for all patients and their first-degree relatives.

Adenomatous Polyposis Coli↗
PubMed1996

Topical versus peribulbar anesthesia in clear corneal cataract surgery.

PURPOSE: To evaluate the efficacy of topical anesthesia as an alternative to peribulbar anesthesia in clear corneal cataract surgery. SETTING: Department of Ophthalmology, University of Vienna, Austria. METHODS: In this prospective, double-blind clinical trial, 36 patients had bilateral cataract surgeries performed from 1 to 3 months apart. Half of the patients had topical anesthesia for the first surgery and peribulbar anesthesia for the second surgery. The other half had peribulbar first and then topical. All surgery was done using a temporal clear corneal approach and bimanual phacoemulsification followed by in-the-bag intraocular lens implantation. Subjective pain was assessed using a visual analog scale of no pain (0%) to worst pain imaginable (100%) and intraoperative motility using a rank scale of adverse motility (-5) to ideal patient cooperation (+5). RESULTS: Subjective pain was comparable whether topical or peribulbar anesthesia was used (mean 10.75 versus 10.97%; P > .6). Patient cooperation (motility) was significantly better when topical anesthesia was used (+2.16 versus +1.11; P = .03). There were no significant differences in complications. A peribulbar block was given in addition to the topical anesthesia in two cases. CONCLUSIONS: Topical anesthesia is a safe, effective alternative to peribulbar anesthesia in clear corneal cataract surgery.

Administration, Topical↗
PubMed1996

TLD array for precise dose measurements in stereotactic radiation techniques.

We developed a new TLD array for precise dose measurement and verification of the spatial dose distribution in small radiation targets. It consists of a hemicylindrical, tissue-equivalent rod made of polystyrene with 17 parallel moulds for an exact positioning of each TLD. The spatial resolution of the TLD array was evaluated using the Leskell spherical phantom. Dose planning was performed with KULA 4.4 under stereotactic conditions on axial CT images. In the Leksell gamma unit the TLD array was irradiated with a maximal dose of 10 Gy with an unplugged 14 mm collimator. The doses delivered to the TLDs were rechecked by diode detector and film dosimetry and compared to the computer-generated dose profile. We found excellent agreement of our measured values, even at the critical penumbra decline. For the 14 mm and 18 mm collimator and for the 11 mm collimator combination we compared the measured and calculated data at full width at half maximum. This TLD array may be useful for phantom or tissue model studies on the spatial dose distribution in confined radiation targets as used in stereotactic radiotherapy.

Humans↗
PubMed1995

Suction fixation system for stereotactic radiosurgery of intraocular malignancies.

We designed a suction fixation system for the radiosurgical treatment of intraocular malignancies with the Leksell gamma unit (gamma knife). OUr device consists of a circular suction chamber and an adjustable unit to be fixed to the Leksell stereotactic head frame. All components are made of plastic materials in order to avoid artifacts in CT or MRT imaging. A permanent suction of 600 to 800 millibars is provided by a standard vacuum pump, powered by a portable battery. Suction times up to 40 minutes were well tolerated in all cases. In the gamma knife of the Neurosurgical Department at the University of Vienna, we successfully used this device. Up to January 1994 we have performed 19 radiosurgical treatments in 9 patients with large or extra-large uveal melanomas and in one patient suffering from a choroidal metastasis.

Aged↗
PubMed1995

Experience with a suction fixation system for stereotactic radiosurgery of intraocular malignancies.

We designed a suction fixation system for the radiosurgical treatment of intraocular malignancies with the Leksell Gamma Knife. Our device consists of a circular suction chamber and an adjustable unit which is fixed to the Leksell stereotactic head frame. All components are made of plastic in order to avoid artifacts in CT or MRI. A permanent suction of 600-800 mbar is provided by a standard vacuum pump, powered by a portable battery. In the Gamma Knife Unit of the Neurosurgical Department at the University of Vienna, we successfully used this device. Up to April 1994 we successfully performed 25 radiosurgical treatments in 12 patients with large or extra-large uveal melanomas and in 1 patient suffering from a choroidal metastasis.

Aged↗
PubMed1994

Influence of existing retinal correspondence on the results of squint operations in alternating convergent strabism.

In our study we examined the influence of existing retinal correspondence on the result of squint operations for alternating convergent strabism. 157 patients under 10 years of age at the time of their first or only operation were included. They were divided into groups, depending on their age at the onset of squint and subgroups according to their type of retinal correspondence. The development of distance and near deviation was investigated separately. Covariance analysis demonstrated that the preoperative sensorial state is a predictor for the motor outcome of surgery with regard to postoperative distance deviation. Statistically we found at least noticeable results (p < 0.15) in all groups of patients--for acquired esotropia a significant result (p < 0.01). With regard to the postoperative near deviation we found a significant influence of the preoperative sensorial state only in the group of patients with a late onset of squint (p = 0.05). For patients with an earlier onset (before the 30th month) of strabismus, the preoperative angle of near deviation proved to have a significant impact on the postoperative development of near deviation (p < 0.05). Sensorio-motorial adaptational phenomena in esotropia are presumed to be the major cause for this difference.

Adaptation, Ocular↗
PubMed1994

[Long-term results of implantation of a plate haptic silicone lens in the capsular sac].

BACKGROUND: An important step in developing cataract surgery was the introduction of soft foldable silicone intraocular lenses in the middle 80's. Functional and morphological long-term data are a vital base for definite conclusions on the new material's safety and biocompatibility. PATIENTS AND METHODS: Our study presents the long-term results after the implantation of a silicone posterior chamber lens with solid plate haptic design (STAAR AA-4203). All lenses were folded and implanted through a 4-mm small corneoscleral incision. Our study includes 54 eyes in 52 patients with a mean follow-up period of 56.5 +/- 8.9 months. RESULTS: A visual acuity of 20/40 or better was found in 90.7% of all eyes. All except one of the 33 eyes without any further preexisting ocular pathology at the time of the operation achieved a visual acuity of 20/40 or better. Two thirds of all eyes had a horizontal astigmatism of +1.0 D or less. By slitlamp examination more or less dispersed pigment was seen on the IOL's surface in 46.3%. 83% of the silicone lenses were centrated within 0.5 mm. A YAG-laser capsulotomy was performed in 7 cases (13%). IOL-related intraocular inflammations, cystoid macular edema or an elevated intraocular pressure did not occur in this group. CONCLUSIONS: Our satisfactory long-term results suggest an excellent biocompatibility of the IOL's design and material.

Aged↗
PubMed1994

Prolonged preoperative prismatic treatment in alternating convergent squint.

Our 10-year retrospective study includes 178 children below the age of 10 years, operated for alternating convergent squint. Inclusion criteria were: Absence of amblyopia and an angle of squint less than 45 pdpt so that alignment of the eyes in only one operation could be expected. One hundred children received preoperatively a prismatic correction of the distance deviation for a period of 6-15 months; 78 cases were treated with glasses and occlusion. In the prism-treated group a significantly better alignment (p = 0.0001) with a motorial gain of 7-8 pdpt was observed 6 months after surgery; also better sensorial results with significantly (p = 0.0001) more cases of stable NRC or harmonious ARC and improved binocularity were achieved. Unlike the type of esotropia, the preexisting retinal correspondence significantly influenced the motorial outcome (p < 0.05). Fewer reoperations were necessary in the prism-treated group (p = 0.001). Our results indicate that a prolonged prismatic correction is an effective preoperative treatment in patients with alternating convergent squint.

Child↗
PubMed1994

Suction attachment for stereotactic radiosurgery of intraocular malignancies.

We designed a suction attachment for the radiosurgical treatment of intraocular malignancies with the Leksell gamma unit (Gamma Knife). Our device consists of a circular suction chamber and an adjustable unit to be fixed to the Leksell stereotactic head frame. All components are made of plastic materials in order to avoid artifacts in CT or MRT imaging. A permanent suction of 600-800 mbar is provided by a standard vacuum pump, powered by a portable battery. Suction times up to 40 min were well tolerated in all cases. We successfully used this device, performing 17 radiosurgical treatments in 8 patients with large or extra-large uveal melanomas and one patient suffering from a choroidal metastasis.

Aged↗
PubMed1993

Choroidal melanomas near the optic disk or macula. Long-term results after proton beam irradiation: a report of 3 cases.

Three patients with choroidal melanomas of the posterior pole were treated with proton beam irradiation. One tumor was medium-sized, two were large-sized. Two of the three eyes were functionally single eyes. 60 CGE (cobalt gray equivalents) was delivered in 4 equal treatments during 4 consecutive days. The minimum follow-up period for each patients is 4 years, the average time 4.8 years. Functionally, we lost both eyes with the large-sized tumors owing to severe radiogenic side effects; the eye containing the largest tumor had to be enucleated after 48 months because of phthisis bulbi. No metastases have developed up to now.

Adult↗
PubMed1993

A warm-water perfusion plaque for hyperthermic treatment of intraocular tumors.

This paper describes the design and performance of a plaque aimed at delivering hot-water hyperthermia to intraocular tumors. The plaque transfers heat into the tissues via conduction. Maximum temperature cannot exceed inflow water temperature. The high water flow rate provided by the hyperthermia unit guarantees an excessive power output at a constant temperature level, resulting in a homogeneous temperature distribution in the tissue. Heat distribution over the plaque surface was shown to be uniform. System performance has been studied on enucleated human as well as on living rabbit eyes. Thermal mapping was done in two and one planes, respectively, and the spatial distribution was calculated. Results promise therapeutic temperature levels to a depth exceeding 10 mm.

Animals↗
PubMed1993

Combined local excision and brachytherapy with ruthenium-106 in the treatment of epibulbar malignancies.

Two patients with epibulbar malignancies were treated by local excision and brachytherapy with ruthenium-106. One patient showed a large melanoma on the epibulbar conjunctiva, the other patient suffered from a recurrent squamous cell carcinoma at the limbus. After excision of the tumor including lamellar sclerectomy and keratectomy, a ruthenium-106 plaque was sutured to the sclera, and a total dose of 290 and 320 Gy, respectively, was delivered to the tumor bed. No severe radiogenic complications were observed except for a rarefaction of the sclera in the treatment area and a slow cataract increase. After a follow-up period of 50 and 22 months, respectively, both patients do not show any recurrence or metastatic disease.

Aged↗