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Biomedical subjects

Thomas Laube

Publications and source records attributed to Thomas Laube.

14 recordsLinked to original sources
PubMed2006

Visualization of the visual cortex in minipigs using fMRI.

Minipigs are widely used to examine physiologic mechanisms under experimental settings. The purpose of our study was to localize the visual cortex of minipigs using visual stimulation in functional magnetic resonance imaging (fMRI). Five male Göttinger minipigs were studied with fMRI during visual stimulation with series of light impulses conducted into the MR cabin via fibre optical wave guides (EPI sequences, block design, 1.5 T clinical routine MR-scanner). Statistics were performed using SPM'99. All minipigs showed activation of the visual cortex due to light stimulation. The activation could be superimposed to T2-weighted structural images with good spatial resolution revealing the exact location of the visual cortex. We were able to localize the visual cortex in minipigs for the first time utilizing fMRI on a routine scanner. However, this may be useful for precise positioning of electrodes or implants or be used as a further uncomplicated non-invasive method in physiologic experiments.

Animals↗
PubMed2005

A method and technical equipment for an acute human trial to evaluate retinal implant technology.

This paper reports on methods and technical equipment to investigate the epiretinal stimulation of the retina in blind human subjects in acute trials. Current is applied to the retina through a thin, flexible microcontact film (microelectrode array) with electrode diameters ranging from 50 to 360 microm. The film is mounted in a custom-designed surgical tool that is hand-held by the surgeon during stimulation. The eventual goal of the work is the development of a chronically implantable retinal prosthesis to restore a useful level of vision to patients who are blind with outer retinal degenerations, specifically retinitis pigmentosa and macular degeneration.

Blindness↗
PubMed2004

X-ray crystal structures of a benzonorbornenyl cation and of a protonated benzonorbornenol.

The crystal structure of the 9-methylbenzonorbornenyl cation Me-1+ shows a relatively strong interaction between the sp(2)-hybridized carbon atom C9 and the aromatic ring (C4a-C9 identical with C8a-C9 = 1.897(10) A). The anion Sb(2)F(11)(-) is refined as rotationally disordered along the Sb...Sb axis. In sharp contrast to the findings about Me-1+, the protonated anti-benzonorbornenol 5+ is essentially an oxonium ion with only weak interaction between the C9 bridge and the aromatic ring despite the fact that it is already a positively charged ion, which upon loss of a water molecule is expected to give the parent cation H-1+. The hydrogen atoms on the oxonium O atom are involved in strong hydrogen bonds to chlorosulfonate anions and probably partially disordered despite the large estimated pK(a) differences between the corresponding acid-base pairs. The experimentally determined cation structures are compared with structures computed by DFT methods. Detailed experimental procedures are given.

Journal Article↗
PubMed2004

Optical energy transfer for intraocular microsystems studied in rabbits.

BACKGROUND: The development of a visual prosthesis aims to restore partial vision in patients with diseases which lead to total photoreceptor loss. The wireless power supply for a retinal implant may be realized with electromagnetic induction or with optical energy transfer. The present study investigates the feasibility of a photovoltaic power generation in the intraocular lens (IOL) part of an epiretinal implant for long-term tests in rabbits. METHODS: IOLs containing an array of photovoltaic cells (PVC) and a light-emitting diode (LED) were implanted into the capsular bag after phacoemulsification in three chinchilla rabbits. Optical energy transfer was established with an infrared laser beam at 850 nm wavelength. Lighting up of the LED proved the functioning of the PVC array. The maximum duration of in vivo functioning of the implant was determined by regular tests involving laser beam application. The explanted microsystems were technically analyzed. Tissues of both eyes underwent routine histological examinations. RESULTS: The lifespan of the microsystems ranged from 14 days to more than 7 months. Final malfunction was caused by PVC defects or by defective contacts between PVC and LED that may originate from the low adhesive strength between the silicone cover and the underlying electronic components. The histological examination showed no alterations of the retinal structure in the treated eyes. CONCLUSIONS: The power supply for intraocular microsystems by an array of photovoltaic cells was proven to be feasible in long-term tests in rabbits. An essential prerequisite for a future device is hermetic coating of the electronics.

Animals↗
PubMed2004

Decreased keratocyte death after laser-assisted subepithelial keratectomy and photorefractive keratectomy in rabbits.

PURPOSE: To compare keratocyte loss in the corneal stroma after laser-assisted subepithelial keratectomy (LASEK) and photorefractive keratectomy (PRK) in rabbits. SETTING: Department of Ophthalmology, University of Essen, Essen, and the Institute of Anatomy, University of Bochum, Bochum, Germany. METHODS: Laser-assisted subepithelial keratectomy and PRK were performed in rabbits and studied 1, 3, 10, and 20 days after surgery. Excimer photoablation was done unilaterally with a 6.0 mm ablation zone and an 80 microm depth, equivalent to -6.0 diopters. Keratocyte death was analyzed using DNA fragmentation-detecting terminal deoxynucleotidyl transferase deoxy-UTR-nick end labeling (TUNEL) assay and transmission electron microscopy. RESULTS: Numerous TUNEL-positive keratocytes occurred 1 day after PRK; the number decreased significantly after 3 days. After LASEK, significantly fewer TUNEL-positive keratocytes were noted at the early time points (P<.001 at 1 day; P< or =.05 at 3 days). At 10 days, the number of TUNEL-positive keratocytes decreased in both groups but remained significantly higher after PRK than after LASEK (P<.001). Twenty days after both procedures, no significant signs of keratocyte death were found in the corneal stroma. Transmission electron microscopy revealed few apoptotic keratocytes after LASEK. After PRK, apoptotic keratocytes, characterized by chromatin condensation, apoptotic bodies, and cell shrinkage, were scattered in the stroma. The ultrastructural findings confirmed the results obtained with the TUNEL assay. CONCLUSIONS: Laser-assisted subepithelial keratectomy induced significantly less apoptotic keratocyte death than PRK and promoted wound healing in the acute phase after photoablation. This procedure may offer the possibility of treating higher myopia with a decreased risk for developing wound healing-related complications known to occur after PRK.

Animals↗
PubMed2004

Ultraviolet radiation absorption of intraocular lenses.

OBJECTIVES: To record and compare the spectral transmittance curves of intraocular lenses (IOLs) made out of polymethyl methacrylate (PMMA), acrylic, hydrogel, and silicone from different manufacturers; to evaluate their ultraviolet radiation absorption capacities; and to contrast the recorded transmittance curves with that of the natural lens. DESIGN: Experimental study. METHODS: We studied 17 different 21-diopter IOLs. A high-performance spectrophotometer with a diffuse transmittance accessory was employed to measure the transmittance of wavelengths from 200 nm to 800 nm through a 1.5-mm aperture. MAIN OUTCOME MEASURES: Transmittance percentage and 10% transmittance cutoff wavelength. RESULTS: All studied IOLs offered good ultraviolet radiation protection in the ultraviolet C (200-280 nm) and ultraviolet B (280-315 nm) ranges. A number of silicone, PMMA, and acrylic lenses showed different and, at times, only low degrees of absorption in the ultraviolet A (315-400 nm) range. CONCLUSIONS: Intraocular lenses of different compositions have ultraviolet radiation absorption characteristics different from that of the crystalline lens.

Absorption↗
PubMed2004

[Endogenous bacterial endophthalmitis: a retrospective study on 22 consecutive cases].

BACKGROUND: Cases of endogenous bacterial endophthalmitis were analysed regarding predisposing factors, timing of diagnosis, sources of infection, causative organisms, and visual outcome. The value of an immediate vitrectomy compared to exclusively injected intravitreal antibiotics was evaluated reviewing the literature. METHODS: Records of 22 consecutive cases of the last 9 years with endogenous bacterial endophthalmitis were reviewed. The identified source of infection was treated with systemic antibiotics. All affected eyes were treated with intraocular injection of antibiotics, whenever possible combined with vitrectomy. RESULTS: 90% of the patients had severe predisposing diseases, primarily diabetes mellitus combined with renal insufficiency and urinary tract infection (70%). Diagnoses were made 3.5 days after beginning of symptoms. An average of 75% of the patients had gram-positive and 25% gram-negative bacteria as causative organisms. Most common gram-positive bacteria were Staphylococcus aureus and S. epidermidis. In 73% of all eyes vitrectomy was used as primary treatment. In 57% of the cases the visual outcome was light perception or better (excluding primary enucleations and deceased patients). 7% of the eyes had no light perception, 36% underwent secondary enucleation. Especially in cases of early diagnoses (less than or equal to 2 days) therapy was successful (60% of the patients); in contrast to delayed diagnoses (33%). The literature review suggests that immediate vitrectomy is superior to exclusive intravitreal injection of antibiotics concerning bulb conservation and remaining function. CONCLUSIONS: Immediate diagnosis and therapy are crucial for a positive outcome in this ophthalmological emergency. Immediate pars plana vitrectomy with intraocular antibiotic instillation seems to improve the prognosis of the affected eyes.

Aged↗
PubMed2003

Chronically implanted epidural electrodes in Göttinger minipigs allow function tests of epiretinal implants.

BACKGROUND: To test the function of implantable devices for electrical stimulation of the retina, long-term registration tests of cortical-evoked potentials are required. Skin electrodes are not appropriate to provide representative recordings, due to the voluminous pneumatic frontal sinus of minipigs. Therefore, epidural electrodes were permanently implanted in minipigs and tested with visual and electrical retinal stimulation. The present study describes long-term recordings of electrically evoked cortical potentials in minipigs. METHODS: Three-channel silver-silver chloride electrodes were fixed on the epidura dorsal to the primary visual cortex of one hemisphere in Göttinger minipigs. Repeated light stimulation was performed and platinum-polyimide film multielectrode arrays were implanted on the retina for electrical stimulation and were later removed. Cortical potentials were recorded after stimulation with short biphasic charge-balanced currents. RESULTS: For up to 18 months, the implanted epidural electrodes allowed recording of visual cortex potentials evoked by visual or electrical retina stimulation. Small changes of response amplitudes in subsequent experiments indicated a stable location and recording properties of the cortex electrodes. Visual stimulation often yielded stronger responses for the contralateral eye. Superthreshold electrical retina stimulation evoked cortical responses with less delay compared to visual stimulation. We found threshold currents of 50 microA for charge-balanced biphasic trains of current impulses. Postoperative examination showed an attached and unchanged retina. CONCLUSIONS: The minipig model is appropriate for the implantation of epiretinal stimulation electrodes and for the long-term tests of retinal implants by recording of cortical responses with chronically implanted epidural electrodes.

Animals↗
PubMed2003

Clorazepate dipotassium versus midazolam for premedication in clear corneal cataract surgery.

PURPOSE: To evaluate and compare the efficacy of oral clorazepate dipotassium (Tranxilium) and intravenous midazolam (Dormicum) as premedication agents in retrobulbar anesthesia and clear corneal phacoemulsification with intraocular lens (IOL) implantation. SETTING: Department of Ophthalmology, University of Essen, Essen, Germany. METHODS: In a prospective clinical trial, 97 consecutive patients (97 eyes) having phacoemulsification with implantation of a foldable IOL were randomized to 2 groups. The first group received 10 mg oral clorazepate dipotassium and the second group, 1 mg intravenous midazolam. The surgeon's subjective experience of patients' cooperation during retrobulbar anesthesia and after surgery was measured on a 5-point Likert scale. The duration of surgery and rate of complications were documented. One day after surgery, the patients' subjective comfort during cataract surgery was evaluated using a 5-point Likert scale and the best corrected visual acuity was determined. RESULTS: The level of anterograde amnesia tended to be higher in the midazolam group than in the clorazepate dipotassium group (4% versus 0% for anesthesia administration; 14% versus 4% for surgery), but the difference between groups was not significant. There were no significant differences in patient cooperation or complications during surgery. Patient satisfaction scores were not significantly different between the groups (P<.14); however, patients in the midazolam group expected to have significantly less pain during surgery (P<.04). The rate of potential visual acuity recovery was similar between groups. CONCLUSIONS: Anterograde amnesia occurred more frequently and patients expected less pain before surgery with midazolam. Both anesthetic agents provided safe and effective premedication for retrobulbar anesthesia in clear corneal cataract surgery.

Administration, Oral↗
PubMed2003

Elliptical ELSA (LASEK) instruments for the treatment of astigmatism.

PURPOSE: To investigate newly designed, elliptical ELSA (excimer laser subepithelial ablation) instruments for the treatment of astigmatism. SETTING: University Eye Clinic Regensburg, Regensburg, Germany, and the Rayne Institute, Department of Ophthalmology, St. Thomas' Hospital, London, United Kingdom. METHODS: The new ELSA instrument set consists of an elliptical microtrephine (11.0 mm x 8.0 mm) with a 70 microm calibrated blade and an elliptical alcohol cone (11.5 mm x 8.5 mm). With this instrument set, ELSA (the laser-assisted subepithelial keratectomy [LASEK] described by Camellin) was performed in 34 astigmatic eyes. The cylindrical correction was between 1.00 diopters (D) and 3.50 D and the spherical correction, between -0.75 D and -8.75 D. In all eyes, the follow-up was 6 months. The postoperative refractive outcome was analyzed using Alpins vector analysis. RESULTS: Excimer laser subepithelial ablation was performed without intraoperative complications in all eyes. At 6 months, the mean spherical correction was -0.04 D +/- 0.27 (SD) (range +0.75 to -0.75 D) and the mean cylindrical correction, 0.27 +/- 0.23 D (range 0 to 0.75 D). The mean index of success was 0.18 +/- 0.15. CONCLUSIONS: With the elliptical instruments, ELSA was an effective and safe surgical procedure for astigmatism.

Astigmatism↗
PubMed2003

[Clinical experiences and results of application of mitomycin C in trabeculectomy].

BACKGROUND: Mitomycin C (MMC) used as an additive agent in glaucoma surgery has been shown to improve the postoperative results of intraocular pressure (IOP), but may also lead to higher incidences of postoperative wound healing disorders and of hypotonia with choroidal detachment. In this retrospective study the levels of IOP, the incidence of complications and changes of the visual acuity (VA) were monitored. METHODS: A trabeculectomy was performed on 70 eyes (57 patients). During surgery MMC was applied in three different concentrations: 0.1 mg/ml MMC (n = 8), 0.2 mg/ml MMC (n = 53) and 0.4 mg/ml MMC (n = 9) for 2.5 minutes, respectively. Patients were reexamined one day, and at 3 and 12 months after surgery. RESULTS: IOP was lowered with high statistical significance at all dates of control examination no matter what concentration of MMC had been used. At the time of discharge from hospital the success rate without additional topical glaucoma medication was 96 %, 78 % after 3 months and 68 % after 12 months. With glaucoma medication the success rate was 92 % after 3 months and 85 % after 12 months. Frequent complications were choroidal detachments in 40 % and hypotonia in 21 % of all cases. The VA did not change significantly during the follow-up period. CONCLUSIONS: This study underlines the efficacy of MMC as an additive agent in glaucoma surgery. However, considerable complications may be expected. Considering the effectiveness and the complication rate a concentration of 0.2 mg/ml MMC should be preferred.

Aged↗
PubMed1999

Empirical Relationship between the Conformation and the Direction of Carbonyl Group Pyramidalization of Cyclohexanones.

A statistical investigation of precise crystal structures from the Cambridge Structural Database shows that cyclohexanones have a predictable pyramidalization of the carbonyl group in the chair conformation that depends on the puckering of the ring. Flattened cyclohexanones are usually "axially pyramidalized" (see Figure 1), whereas more strongly puckered cyclohexanones are usually "equatorially pyramidalized". It is conceivable that a cooperation between electronic effects (hyperconjugation) and steric effects (relief from torsional strain) leads to this unique correlation. No such conformation/pyramidalization correlations are observed for other ketones.

Journal Article↗
PubMedDate not supplied

Long-term effect of acetazolamide treatment of patients with uveitic chronic cystoid macular edema is limited by persisting inflammation.

PURPOSE: To assess the long-term effect of acetazolamide treatment on patients with cystoid macular edema (CME) in the course of intermediate or posterior chronic uveitis and to define those patients who may particularly benefit from the drug. METHODS: Fifty-two eyes (45 patients) with chronic uveitic CME were treated with acetazolamide at an initial dosage of 500 mg/d. The effect of treatment was assessed by fluorescein angiography, ophthalmoscopy, visual acuity, and Amsler testing. Therapy was withdrawn when CME did not improve at 3 weeks. In cases with CME improvement, the dosage was gradually tapered. RESULTS: The mean follow-up was 3.1 years (minimum, 1.5 years). Two subgroups were identified: group 1, quiescence of uveitis with acetazolamide as the single therapeutic agent (33 eyes); and group 2, chronically active uveitis requiring additional systemic antiinflammatory drugs (19 eyes). In both groups, visual acuity improvement was statistically significant (group 1, P = 0.012; group 2, P = 0.025). In 12 patients with a stable visual acuity gain, the medication dose could be tapered off completely without any recurrent edema shown by fluorescein angiography after a minimum follow-up of 1 year. Sixteen patients required a maintenance dosage, ranging from 125 to 500 mg daily. No major adverse effects of the medication were observed. CONCLUSIONS: During long-term follow-up, low-dose acetazolamide can be a useful therapeutic option for chronic CME in uveitis. The effect was better in patients with quiescence of uveitis than in those with chronically active uveitis. Permanent therapy is not imperative in every case.

Acetazolamide↗