Biomedical subjects

G Rainer

Publications and source records attributed to G Rainer.

At least 37 records · Page 2Linked to original sources

PubMed2000

Hypercapnia-induced cerebral and ocular vasodilation is not altered by glibenclamide in humans.

Carbon dioxide is an important regulator of vascular tone. Glibenclamide, an inhibitor of ATP-sensitive potassium channel (K(ATP)) activation, significantly blunts vasodilation in response to hypercapnic acidosis in animals. We investigated whether glibenclamide also alters the cerebral and ocular vasodilator response to hypercapnia in humans. Ten healthy male subjects were studied in a controlled, randomized, double-blind two-way crossover study under normoxic and hypercapnic conditions. Glibenclamide (5 mg po) or insulin (0.3 mU. kg(-1). min(-1) iv) were administered with glucose to achieve comparable plasma insulin levels. In control experiments, five healthy volunteers received glibenclamide (5 mg) or nicorandil (40 mg) or glibenclamide and nicorandil in a randomized, three-way crossover study. Mean blood flow velocity and resistive index in the middle cerebral artery (MCA) and in the ophthalmic artery (OA) were measured with Doppler sonography. Pulsatile choroidal blood flow was assessed with laser interferometric measurement of fundus pulsation. Forearm blood flow was measured with venous occlusion plethysmography. Hypercapnia increased ocular fundus pulsation amplitude by +18.2-22.3% (P < 0. 001) and mean flow velocity in the MCA by +27.4-33.3% (P < 0.001), but not in the OA (2.1-6.5%, P = 0.2). Forearm blood flow increased by 78.2% vs. baseline (P = 0.041) after nicorandil administration. Glibenclamide did not alter hypercapnia-induced changes in cerebral or ocular hemodynamics and did not affect systemic hemodynamics or forearm blood flow but significantly increased glucose utilization and blunted the nicorandil-induced vasodilation in the forearm. This suggests that hypercapnia-induced changes in the vascular beds under study are not mediated by activation of K(ATP) channels in humans.

Adenosine Triphosphate↗

PubMed2000

Task-specific neural activity in the primate prefrontal cortex.

Real-world behavior is typically more complicated than a one-to-one mapping between a stimulus and response; the same stimulus can lead to different behaviors depending on the situation, or the same behavior may be cued by different stimuli. In such cases, knowledge of the formal demands of the task at hand is required. We found that in monkeys trained to alternate between three tasks, the activity of many neurons in the prefrontal cortex was task dependent. This included changes in overall firing rate, in firing-rate profiles (shape of responses over time), and in stimulus and response selectivity. These findings support the hypothesis that a major prefrontal function is the acquisition and implementation of task context and the "rules" used to guide behavior.

Animals↗

PubMed1999

Prospective coding for objects in primate prefrontal cortex.

We examined neural activity in prefrontal (PF) cortex of monkeys performing a delayed paired associate task. Monkeys were cued with a sample object. Then, after a delay, a test object was presented. If the test object was the object associated with the sample during training (i.e., its target), they had to release a lever. Monkeys could bridge the delay by remembering the sample (a sensory-related code) and/or thinking ahead to the expected target (a prospective code). Examination of the monkeys' behavior suggested that they were relying on a prospective code. During and shortly after sample presentation, neural activity in the lateral PF cortex primarily reflected the sample. Toward the end of the delay, however, PF activity began to reflect the anticipated target, which indicated a prospective code. These results provide further confirmation that PF cortex does not simply buffer incoming visual inputs, but instead selectively processes information relevant to current behavioral demands, even when this information must be recalled from long-term memory.

Action Potentials↗

PubMed1999

Effects of peribulbar anesthesia on ocular blood flow in patients undergoing cataract surgery.

PURPOSE: The effects of extraconal, peribulbar anesthesia on ocular blood flow may be caused by concomitant elevations in intraocular pressure or direct pharmacologic alteration of vascular tone. We quantified the effect on ocular circulation with a new technique for assessment of ocular hemodynamics. METHODS: In a prospective study, ocular hemodynamics were measured before and 1 and 5 minutes after peribulbar anesthesia in 22 eyes with age-related cataract. Measurements included fundus pulsation amplitude with a laser interferometric method assessing the pulsatile choroidal blood flow and mean blood flow velocity as well as resistive index in the ophthalmic and central retinal artery with Doppler sonography. Systemic blood pressure and pulse were monitored throughout the period of ocular hemodynamic measurements. RESULTS: Fundus pulsation amplitude decreased significantly after peribulbar anesthesia (after 1 minute and 5 minutes: -13% and -8%; P < .001). In the central retinal artery, mean blood flow velocity dropped (-15%; P < .001) and resistive index increased (+3%; P = .02) 1 minute after peribulbar anesthesia compared with baseline. There were no changes in ophthalmic artery hemodynamics. Intraocular pressure was elevated 1 minute after peribulbar anesthesia (+29%; P = .003) but reached baseline values after 5 minutes. CONCLUSION: Pulsatile choroidal blood flow and retinal blood flow velocities were reduced after peribulbar anesthesia. These reductions were still present 5 minutes after peribulbar anesthesia, when intraocular pressure had returned to baseline values. This supports the theory of drug-induced vasoconstriction after peribulbar anesthesia. A loss of vision may be a risk of peribulbar anesthesia in patients who have compromised ocular blood flow before surgery.

Adult↗

PubMed1999

Changes in intraocular lens position after neodymium: YAG capsulotomy.

PURPOSE: To quantify changes in intraocular lens (IOL) position caused by neodymium: YAG (Nd:YAG) capsulotomy with 3 IOL styles. SETTING: Department of Ophthalmology, University of Vienna, Austria. METHODS: In a prospective study, anterior chamber depth (ACD) was measured by dualbeam partial coherence interferometry (PCI) in 32 pseudophakic eyes of 32 patients with posterior capsule opacification before and immediately after planned capsulotomy under mydriasis. Patients were divided into 3 groups with the following IOL styles: 1-piece poly(methyl methacrylate) (PMMA), 3-piece foldable, and plate haptic. RESULTS: The capsulotomy induced a backward IOL movement in all 32 eyes (mean 25 microns; range 9 to 55 microns). It was more pronounced in eyes with plate-haptic IOLs than in those with the other styles. Precision of ACD measurement by PCI was 4 microns. Changes in ACD correlated significantly with capsulotomy size but not with preoperative lens-capsule distance. CONCLUSION: Capsulotomy caused a backward movement of the IOL, which was more pronounced with plate-haptic IOLs than with 1-piece PMMA and 3-piece foldable IOLs. Since the magnitude of IOL movement in this study population was small, a hyperopic shift in refraction after capsulotomy will usually be small and not clinically relevant.

Adult↗

PubMed1999

Contact zone of piggyback acrylic intraocular lenses.

In a hyperopic cataract patient, surgery was performed with implantation of 2 foldable, acrylic, posterior chamber intraocular lenses (IOLs) in the bag. The IOLs showed a central contact zone during surgery. This contact zone remained after surgery and was documented 2 months postoperatively. The contact zone may induce multifocality similar to that seen with multifocal IOLs.

Acrylic Resins↗

PubMed1999

Effect of small incision cataract surgery on ocular blood flow in cataract patients.

PURPOSE: To evaluate the effect of small incision cataract surgery using peribulbar anesthesia on ocular blood flow in patients with senile cataract. SETTING: Department of Ophthalmology, University of Vienna, Vienna, Austria. METHODS: In 33 eyes of 33 consecutive patients scheduled for cataract surgery, ocular hemodynamics were measured preoperatively and 1 day, 1 week, and 1 month postoperatively. Measurements included fundus pulsation amplitude (FPA) with a laser interferometric method that assessed the pulsatile choroidal blood flow, mean blood flow velocity (MFV), and resistive index (RI) in the ophthalmic artery (OA) and the central retinal artery (CRA) with Doppler sonography. Systemic hemodynamics and intraocular pressure (IOP) also were measured. RESULTS: The FPA, MFV, and RI in the OA and the CRA did not change postoperatively from baseline values. Systemic hemodynamics, IOP, and as a consequence ocular perfusion pressure, also remained unchanged. CONCLUSION: Uneventful small incision cataract surgery using peribulbar anesthesia did not affect ocular blood flow in patients with senile cataract between 1 day and 1 month postoperatively.

Adult↗

PubMed1999

Corneal shape changes after temporal and superolateral 3.0 mm clear corneal incisions.

PURPOSE: To compare the corneal topographic changes after temporal and superolateral 3.0 mm clear corneal incisions (CCIs) and implantation of foldable silicone intraocular lenses (IOLs). SETTING: Department of Ophthalmology, University of Vienna, Austria, and a private clinic, Winterthur, Switzerland. METHODS: This prospective study comprised 54 eyes of 54 patients scheduled for cataract surgery. After a 0.3 mm deep precut, a temporal 3.0 mm CCI was made in 26 eyes and a superolateral (at 10:30) 3.0 mm CCI in 28 eyes. Corneal topography was recorded preoperatively and 1 week and 1 and 3 months postoperatively using the TMS-1 computer-assisted videokeratoscope (Computed Anatomy, Inc.). Surgically induced corneal shape changes were evaluated by batch-by-batch analyses of the paired differences between the records. The significance of topographic changes was calculated by the paired Wilcoxon test; group comparisons were made using the Wilcoxon group comparison test. RESULTS: Both groups had incision-related corneal flattening at 1 week and 1 and 3 months postoperatively. The extent of this flattening at 1 week and 1 and 3 months postoperatively was up to 1.0, 0.9, and 0.7 diopter (D), respectively, in the temporal group and up to 1.2 D at each observation time in the superolateral group. There was statistically significantly more incision-related corneal flattening in the superolateral incision group than in the temporal incision group; the difference was up to 0.3 D after 1 month and 0.5 D after 3 months. CONCLUSION: The superolateral incision induced statistically significantly more incision-related corneal flattening than the temporal incision.

Astigmatism↗

PubMed1999

Prediction of pseudophakic capsular bag diameter based on biometric variables.

PURPOSE: To measure the capsular bag diameter (CBDm) in vivo and calculate a regression formula for future preoperative prediction of capsular bag diameter (CBDp). SETTING: Department of Ophthalmology, University of Vienna, Austria. METHODS: This prospective study comprised 70 eyes having cataract surgery with implantation of an open capsular tension ring (CTR) (Morcher Type 14). Within the first postoperative days, the distance between the ends of the CTR were measured through a gonioscopy lens by adjusting the slit height. This distance was added to the known length of the CTR to calculate the capsular bag circumference and from this, the CBDm. The CBDm was correlated with axial eye length (AL), corneal power (P), preoperative anterior chamber depth and lens thickness, corneal diameter, and age. A stepwise multiple regression analysis was computed with CBDm as the dependent variable. RESULTS: The mean CBDm was 10.37 mm +/- 0.25 (SD). A statistically significant negative correlation was found between CBDm and P (P < .0004; r2 = 0.16) and a positive correlation between CBDm and AL (P < .0226, r2 = 0.07). Stepwise multiple regression resulted in the following regression formula: CBDp = 3.44 to 0.056 x P + 0.713 x AL - 0.0135 x AL2 (P < .0001; r2 = 0.3145). Using this formula with the individual Ps and ALs, all 6 eyes with a large capsular bag diameter (CBDm > 10.7 mm) and 10 of 13 eyes with a small one (CBDm < 10.1 mm) were correctly classified. CONCLUSION: The capsular bag diameter in vivo correlated negatively with corneal power (P) and positively with AL. The regression formula used may serve as a tool for preoperative identification of eyes with a very large or very small CBDm.

Aged↗

PubMed1999

Effect of dorzolamide and latanoprost on intraocular pressure after small incision cataract surgery.

PURPOSE: To evaluate the effect of dorzolamide 2% and latanoprost 0.005% on intraocular pressure (IOP) after small incision cataract surgery. SETTING: Department of Ophthalmology, University of Vienna, Vienna, Austria. METHODS: This prospective study comprised 102 eyes of 102 consecutive patients scheduled for small incision cataract surgery. The patients were assigned preoperatively to 1 of 3 groups of 34 each: dorzolamide, latanoprost, and control (no treatment). One drop of the assigned medication was instilled immediately after surgery. Intraocular pressure was measured preoperatively and 6 and 20 to 24 hours postoperatively. RESULTS: Six hours after surgery, the mean increase in IOP was 1.9 mm Hg +/- 3.9 (SD) in the dorzolamide group (P = .004 versus control), 2.2 +/- 3.0 mm Hg in the latanoprost group (P = .005 versus control), and 4.8 +/- 5.2 mm Hg in the control group. Twenty to 24 hours postoperatively, IOP decreased a mean of -0.9 +/- 3.5 mm Hg in the dorzolamide group (P = .012 versus control) and increased a mean of 0.3 +/- 3.6 mm Hg in the latanoprost group (P = 0.24 versus control) and 1.3 +/- 4.2 mm Hg in the control group. One eye in the dorzolamide group, 1 eye in the latanoprost group, and 4 eyes in the control group had an IOP of 30 mm Hg or higher 6 hours postoperatively. CONCLUSION: Six hours postoperatively, dorzolamide and latanoprost were effective in reducing the IOP increase after small incision cataract surgery; however, at 20 to 24 hours, only dorzolamide was effective. Neither drug prevented IOP spikes of 30 mm Hg or higher.

Aged↗

PubMed1999

[Etiology of non-penetrating corneal injuries].

BACKGROUND: Non-penetrating injuries of the cornea are frequent. Complications like corneal infiltrations, or corneal ulcera, may follow. MATERIAL AND METHODS: This prospective study included 144 patients with non-penetrating corneal injuries. Records contained epidemiological data, field of activity, profession, cause of the injury, and stress during the trauma. RESULTS: 97% of the patients were men, 78% of the injuries occurred during working hours, 41% of the patients were from metal working professions, 73% of the accidents happened with grinding machines and drilling machines. Only 6.9% of patients weared adequate glasses. The cause of trauma was deflection and working without glasses. In 32% of patients stress played a role in the cause of injuries. CONCLUSIONS: Most of the corneal, non penetrating injuries happened during the working hours by deflection, and by neglecting safety glasses. With the use of safety glasses the number of corneal non-penetrating injuries could definitely be reduced.

Accidents, Occupational↗

PubMed1999

Acetazolamide-induced cerebral and ocular vasodilation in humans is independent of nitric oxide.

Acetazolamide, a carbonic anhydrase inhibitor, is used orally in the treatment of primary and secondary open-angle glaucoma and induces ocular and cerebral vasodilation. Several in vitro studies have shown that carbonic anhydrase pharmacology and the L-arginine-nitric oxide (NO) pathway are closely related. We investigated the role of NO in acetazolamide-induced vasodilation on cerebral and ocular vessels in 12 healthy subjects in the presence or absence of NG-monomethyl-L-arginine (L-NMMA), a NO synthase inhibitor, and in the presence or absence of L-arginine, the precursor of NO. Acetazolamide was administered after pretreatment with either L-NMMA or placebo and either L-arginine or placebo. Pulsatile choroidal blood flow was assessed with laser interferometric measurement of fundus pulsation. In addition, mean blood flow velocity (MFV) in the middle cerebral artery (MCA) and ophthalmic artery (OA) was measured with Doppler sonography. Acetazolamide increased ocular fundus pulsation amplitude (FPA; +27%, P < 0.001) and MFV in the MCA (+38%, P < 0.001) and in the OA (+19%, P = 0.003). Administration of L-NMMA alone reduced FPA (-21%, P < 0.001) and MFV in the MCA (-11%, P = 0. 030) but did not change MFV in the OA. All hemodynamic effects of L-NMMA were reversed by L-arginine. However, neither L-NMMA nor L-arginine altered acetazolamide-induced changes in cerebral or ocular hemodynamic parameters. The present data indicate that acetazolamide-induced hemodynamic changes are not mediated by NO. Which mediators other than NO are involved in the hemodynamic effects as induced by carbonic anhydrase inhibitors remains to be elucidated.

Acetazolamide↗

PubMed1998

Memory fields of neurons in the primate prefrontal cortex.

Many prefrontal (PF) neurons convey information about both an object's identity (what) and its location (where). To explore how they represent conjunctions of what and where, we explored the receptive fields of their mnemonic activity (i.e., their "memory fields") by requiring monkeys to remember both an object and its location at many positions throughout a wide portion of central vision. Many PF neurons conveyed object information and had highly localized memory fields that emphasized the contralateral, but not necessarily foveal, visual field. These results indicate that PF neurons can simultaneously convey precise location and object information and thus may play a role in constructing a unified representation of a visual scene.

Animals↗

PubMed1998

Selective representation of relevant information by neurons in the primate prefrontal cortex.

The severe limitation of the capacity of working memory, the ability to store temporarily and manipulate information, necessitates mechanisms that restrict access to it. Here we report tests to discover whether the activity of neurons in the prefrontal (PF) cortex, the putative neural correlate of working memory, might reflect these mechanisms and preferentially represent behaviourally relevant information. Monkeys performed a 'delayed-matching-to-sample' task with an array of three objects. Only one of the objects in the array was relevant for task performance and the monkeys needed to find that object (the target) and remember its location. For many PF neurons, activity to physically identical arrays varied with the target location; the location of the non-target objects had little or no influence on activity. Information about the target location was present in activity as early as 140ms after array onset. Also, information about which object was the target was reflected in the sustained activity of many PF neurons. These results suggest that the prefrontal cortex is involved in selecting and maintaining behaviourally relevant information.

Animals↗

PubMed1998

Partial coherence interferometry: a novel approach to biometry in cataract surgery.

PURPOSE: To compare biometry performed by an enhanced version of dual beam partial coherence interferometry and applanation ultrasound in a prospective study of 85 cataract eyes to improve refractive outcome of cataract surgery due to a more accurate calculation of intraocular lens power. METHODS: The SRK II formula using ultrasound biometry data was employed. Three months after surgery, partial coherence interferometry biometry was repeated and refractive outcome was determined. Preoperative partial coherence interferometry biometry data were used to determine the refractive power of the intraocular lenses retrospectively and to calculate the possible refractive outcome. RESULTS: Precision of partial coherence interferometry biometry was more than 10 times better than that of ultrasound. Therefore, the possible mean absolute error for postoperative refraction achieved with partial coherence interferometry biometry was 0.49 diopters (compared with 0.67 diopters with ultrasound biometry), resulting in an improvement of 27%. Axial eye length measured with the two techniques differed by a mean of 460 microm. The difference in lens thickness measured with partial coherence interferometry and ultrasound significantly correlated with cataract grade. A mean shortening of 120 microm of axial eye length following cataract surgery was also detected by partial coherence interferometry. CONCLUSIONS: The enhanced version of partial coherence interferometry offers biometry with unprecedented precision (<10 microm) and resolution (approximately 12 microm), therefore improving the refractive outcome in cataract surgery. This noninvasive technique provides a high degree of comfort for the patient, with no need for local anesthesia or pupil dilation and minimized risk of corneal infection.

Adult↗

PubMed1998

Reversal of endothelin-1-induced ocular hemodynamic effects by low-dose nifedipine in humans.

BACKGROUND AND PURPOSE: There is evidence that calcium channel blockers may be useful in patients with normal tension glaucoma and vasospastic reactions. We therefore hypothesized that calcium channel blockers may increase ocular blood flow and that there may be a functional antagonism between endothelin-1 (ET-1) and calcium channel blockers in the ocular vasculature. METHODS: This was a randomized, double-blind, three-way crossover study with respect to ET-1 infusions (placebo, 2 ng/kg/min ET-1, and 4 ng/kg/min ET-1) and a randomized double-blind study in two parallel groups with respect to nifedipine (placebo or 5 mg nifedipine). Ocular hemodynamics in the 12 healthy subjects participating in the study was assessed by laser interferometric measurement of fundus pulsation amplitude (FPA) in the optic disc and two-dimensional scanning laser Doppler flowmetry in the optic disc. RESULTS: ET-1 caused a dose-dependent decrease in FPA and flow. With a dose of 4 ng/kg/min a decrease of -18% +/- 5% (p < 0.001) and -17% +/- 5% (p = 0.023) on FPA and flow, respectively, were observed. This effect was completely reversed by nifedipine compared with placebo (FPA, p < 0.001; flow, p = 0.011). However, nifedipine did not affect ocular hemodynamics after placebo infusion. CONCLUSIONS: These results show that nifedipine does not increase optic nerve head blood flow during baseline conditions but reverses ET-1-induced constriction in ocular vasculature at doses that do not affect systemic hemodynamics. This supports the close relation of the therapeutic effect of calcium channel blockers in patients with normal tension glaucoma to the endothelin system. Moreover, the present study provides a strong rationale for a study of low dose nifedipine as a supplementary medication in glaucoma patients.

Adult↗

PubMed1998

Accurate determination of effective lens position and lens-capsule distance with 4 intraocular lenses.

PURPOSE: To measure effective lens position (ELP) of 4 intraocular lenses (IOLs) using high precision and high resolution dual-beam partial coherence interferometry (PCI) and to assess the tendency of these IOLs to produce a lens-capsule distance (LCD), a possible risk factor for posterior capsule opacification. SETTING: Department of Ophthalmology, Vienna General Hospital; Institute of Medical Physics, University of Vienna, Austria. METHODS: In a retrospective study, PCI was used to measure ELP and LCD in 139 pseudophakic eyes of 110 patients with 4 IOLs: acrylic 3-piece IOL (AcrySof MA60BM); silicone 3-piece IOL without a capsular tension ring (PhacoFlex SI30) and with a capsular tension ring (PhacoFlex SI30 and Morcher Type 14); silicone plate-haptic IOL (Staar AA4203VF); and a hydrogel plate-haptic IOL (logel 1103). RESULTS: The ELP and LCD were determined with a precision of approximately 3 to 4 microns. An LCD was detected in 21% eyes with the AcrySof, 20% of eyes with the SI30 without a capsular tension ring, 10% of eyes with a capsular tension ring, 21% of eyes with the Staar, and 17% of eyes with the logel. The LCDs detected by PCI, but not by slitlamp examination, were significantly smaller than those detected by both. CONCLUSION: The amount of LCD detected by PCI was approximately the same with all IOL types (approximately 20%) except the PhacoFlex SI30 with a capsular tension ring (10%).

Acrylates↗

PubMed1998

Comparative study of corneal topographic changes after 3.0 mm beveled and hinged clear corneal incisions.

PURPOSE: To compare the corneal topographic changes after cataract surgery using 2 types of clear corneal incisions (CCIs). SETTING: Department of Ophthalmology, University of Vienna, Austria. METHODS: This prospective, unmasked, nonrandomized study comprised 64 eyes scheduled for cataract surgery; 29 eyes received a temporal sutureless 3.0 mm corneal beveled CCI and 35 eyes, a temporal sutureless 3.0 mm hinged CCI. Preoperatively and 1 week, 1 and 3 months, and 1 year postoperatively, corneal topography was recorded by computer-assisted videokeratoscopy (TMS-1, Computed Anatomy, Inc.). Data were evaluated by batch-by-batch analyses of the paired differences between these records. The significance of topographic changes was calculated by paired Wilcoxon tests, and group comparisons were made using Wilcoxon tests. RESULTS: In both groups, there was statistically significant horizontal flattening and lower corneal steepening (P < .01). The horizontal flattening decreased between 1 week and 1 year, from -0.6 to -0.3 diopter (D) in the beveled-incision group and -0.7 to -0.4 D in the hinged-incision group. Vertical steepening was significant in the lower corneal region and decreased between 1 week and 1 year, from 0.3 to 0.2 D. Group comparisons revealed significant differences in an oblique lower temporal semimeridian, with 0.1 to 0.3 D more steepening after the hinged incision than after the beveled incision (P < .05). CONCLUSION: There were only minimal differences between beveled and hinged CCIs in surgically induced corneal shape changes.

Cornea↗