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Biomedical subjects

O Geyer

Publications and source records attributed to O Geyer.

At least 19 recordsLinked to original sources
PubMed1999

Pulsatile ocular blood flow in diabetic retinopathy.

PURPOSE: To assess circulatory properties of eyes with progressive stages of diabetic retinopathy. METHODS: The intraocular pressure, pulse amplitude (PA) and pulsatile ocular blood flow (POBF) were measured with a pneumatonometer (OBF Labs UK Ltd). The eyes were grouped: (a) normal control, n = 26, (b) diabetes with no observable diabetic retinopathy (NDR), n = 18, (c) mild to moderate non-proliferative diabetic retinopathy (NPDR), n = 20, and (d) very severe pre-proliferative and proliferative diabetic retinopathy (PPDR/PDR), n = 12. RESULTS: The PA and POBF values were lower than normal values in the earliest stage (NDR). The POBF increased but was still below normal levels at the NPDR stage, and then increased to an above normal level in the PPDR/PDR stage of diabetic retinopathy. The PA was at normal levels in these later two stages. CONCLUSION: An initial decrease in pulsatile ocular blood flow is present with the onset of diabetes where no diabetic retinopathy has yet occurred. Subsequently, the pulsatile ocular blood flow increases with the severity of the retinopathy.

Aged↗
PubMed1998

Beta3-adrenergic relaxation of bovine iris sphincter.

Bovine iris sphincter in vitro responded to beta-adrenergic stimulation with pronounced relaxation (EC50 of isoproterenol = 0.3 nM), which was potentiated by the cAMP phosphodiesterase inhibitor, isobutylmethylxanthine, and mimicked by the adenylyl cyclase activator, forskolin. The beta1/beta2 antagonist, propranolol, exhibited low potency with calculated Ki of 200 nM. The beta3-selective antagonist, bupranolol, exhibited a biphasic inhibition profile, with calculated Kis of approximately 20-50 and 200-300 nM. The beta3-selective agonist, BRL 37344, elicited 70% of maximal relaxation (EC50 = 30 nM). When relaxation was induced by BRL 37344, bupranolol exhibited much higher potency (calculated Ki = 1 nM). Our data suggest that the beta-adrenergic relaxation response in bovine iris sphincter is mediated by a mixed population of beta-adrenergic receptors, with a predominant contribution of atypical, most likely beta3 subtype, receptors.

Adrenergic beta-Agonists↗
PubMed1998

Elevated tear interleukin-6 levels in patients with Sjögren syndrome.

OBJECTIVE: The purpose of the study was to investigate interleukin-6 (IL-6) levels in the tear fluid and sera of patients with Sjögren syndrome (SS). PARTICIPANTS: Twelve patients with primary SS and 12 normal control subjects participated. INTERVENTION: Tear fluid and sera were obtained from the study and the control groups. Evaluation of tear fluid and sera IL-6 levels was done by using a quantitative enzyme-linked immunosorbent assay kit. All assays were carried out blindly with respect to diagnosis. MAIN OUTCOME MEASURES: Tear fluid IL-6 levels were measured. RESULTS: The mean concentration (+/- standard error) of IL-6 in the tears of patients with SS was elevated significantly compared to that of normal control subjects (88.6+/-16.2 vs. 42.1+/-10.6 pg/ml; P < 0.05). No significant differences were noted in the serum IL-6 levels between the two groups. A significant correlation (r = 0.742, P = 0.006) was found between tear fluid IL-6 levels and the focus score of lip biopsy specimens in patients with SS. CONCLUSION: Tear fluid IL-6 levels may serve as an important marker for tear gland involvement in SS.

Biomarkers↗
PubMed1998

Management of large, leaking, and inadvertent filtering blebs with the neodymium:YAG laser.

OBJECTIVE: The purpose of the study was to test the efficacy of the neodymium:YAG (Nd:YAG) laser for repairing filtering blebs. DESIGN: The study design was a prospective study. PARTICIPANTS: Five eyes of five patients with leaking blebs (group 1), five eyes of five patients with large irritating blebs (group 2), and four eyes of four patients with inadvertent filtering blebs in the surgical wound after cataract surgery (group 3) were studied. INTERVENTION: The thermal mode of the Lasag Microrupter II Nd:YAG laser was used to treat the filtering blebs. The area of the bleb targeted for treatment was "painted" with methylene blue and then exposed to Nd:YAG laser treatment with an energy level of 2.5 to 3.75 J in a grid pattern. The aiming beam was focused on the conjunctiva, but the laser beam was offset according to the height of the bleb (offset of 0.9-1.5 mm, 4-5 on the Lasag) to selectively treat the internal surface of the bleb. MAIN OUTCOME MEASURES: Symptomatology, intraocular pressure (IOP), and complications were measured. RESULTS: After the laser treatment, all the leaks in group 1 were healed, all the patients in group 2 reported relief of their symptoms, and all blebs in group 3 shrank considerably. The IOP increased significantly (P < 0.001) after laser treatment in all three groups. This elevation appeared to diminish over time, with the major increase in IOP being recorded within the first month after the laser treatment. However, satisfactory IOP control was maintained in nearly all patients (13 to 14) who received none or one antiglaucoma medication. The visual acuity of one patient decreased significantly because of cataract formation. Complications included transient pressure rise (1 eye), bleb failure (1 eye), pupillary retraction toward the bleb (6 eyes), iatrogenic bleb leak (6 eyes), and cataract (1 eye). CONCLUSION: The continuous wave Nd:YAG laser is an effective tool for repairing bleb-related problems while maintaining successful filtration.

Aged↗
PubMed1998

Capsular bag distension associated with sulcus implantation of intraocular lenses.

Capsular bag distension syndrome after endophacoemulsification and in-the-bag intraocular lens (IOL) implantation has been reported. We describe 2 cases in which sulcus implantation of a posterior chamber IOL caused marked capsular bag distension. Both cases resolved with conservative treatment or a neodymium:YAG posterior capsulotomy.

Aged↗
PubMed1998

Iris retraction syndrome associated with nonrhegmatogenous retinal detachment.

PURPOSE: To present the first documentation of iris retraction syndrome in eyes with nonrhegmatogenous retinal detachment. PATIENTS AND METHODS: One patient with age-related macular degeneration and another with panuveitis developed exudative retinal detachment with iris retraction configuration. Ultrasound biomicroscopy was performed to investigate the anatomic relationship of structures in the anterior segment of the eye. RESULTS: Ultrasound biomicroscopy demonstrated a severe backward bowing of the peripheral iris with irido-ciliary body and irido-zonular contact as well as broad iris lens touch. The iris retraction syndrome resolved after pupil dilation and disruption of the pupillary adhesions in both cases. The retinal detachment resolved several months later, without surgery. CONCLUSION: Iris retraction syndrome appears not to be exclusive to rhegmatogenous retinal detachment but can present in eyes with exudative - nonrhegmatogenous retinal detachment. Thus, when the configuration of the iris shows bowing in patients with retinal detachment, iris retraction syndrome should be considered and prompt pupil dilation should be carried out.

Aged↗
PubMed1998

Reproducibility of topographic measures of the glaucomatous optic nerve head.

AIMS/BACKGROUND: Laser scanning tomography provides an assessment of three dimensional optic disc topography. For the clinical purpose of follow up of glaucoma patients, the repeatability of the various measured variables is essential. In the present study, the reproducibility of morphometric variables calculated by the topographic scanning system, TopSS (Laser Diagnostic Technology, San Diego, CA) was investigated. METHODS: Two independent measurements (30 minutes apart) each consisting of three complete images of the optic disc were performed on 16 eyes of 16 glaucoma patients using a TopSS. The instrument calculates 14 morphometric variables for the characterisation of the optic disc. RESULTS: From the two tailed paired tests, all variables were seen to have good reproducibility. However, correlation and regression analyses showed that only the three variables, volume below, half depth area, and average cup depth, are acceptably reproducible. CONCLUSION: The TopSS provides three variables which describe the physiological shape of the optic disc that have high reproducibility. These three variables might be useful for following the progression of optic disc changes in glaucoma patients.

Aged↗
PubMed1997

Nitric oxide synthase activity in tissues of the bovine eye.

BACKGROUND: Nitric oxide synthase (NOS) is present in many ocular tissues where it may have different physiological functions. This warrants a thorough characterization of NOS activity in the eye. METHODS: NOS distribution and its biochemical properties were determined in the retina, choroid, ciliary processes (CP), and trabecular meshwork (TM). RESULTS: Retinal NOS required NADPH (diphenylene-iodonium, a flavoprotein inhibitor, which inhibited enzyme activity with an IC50 of 0.36 microM, FAD (40 microM), FMN (40 microM), and BH4 (4 microM) as cofactors for optimal activity. Ocular NOS appeared to be regulated by free divalent cations, since its activity was inhibited by EDTA (slopes > 3.0 and IC50 values of 12.8, 19.7, and 53 microM, respectively). Ocular NOS required calmodulin, since NOS activity was inhibited by trifluoperazine (calmodulin inhibitor, IC50 = 41 microM). NOS activity is widely distributed in the eye, (choroid > retina > CP > TM) and is mainly cytosolic (70-95%). L-Arginine analogs inhibited NOS in the retina, choroid, and TM. In all three tissues, NG-methyl-L-arginine displayed the highest affinity for inhibition (IC50 = 0.2-0.7 microM) followed by canavanine (IC50 = 13-33 microM), while aminoguanidine only weakly inhibited NOS (IC50 = 93-179 microM). CONCLUSION: In all tissues, the order of potency of inhibition points to the presence of constitutive rather than inducible NOS. Moreover, it is possible that TM contains more than a single form of NOS.

Animals↗
PubMed1997

[Effect of nifedipine on ocular pulse amplitude in normal pressure glaucoma].

BACKGROUND: Ocular pulse amplitude (OPA) is reduced in normal tension glaucoma (NTG) patients when compared to non-glaucomatous, healthy control subjects. This might be related to a vasospastic reaction. The objective of this study was to determine if low OPA in NTG is associated with a vasospastic reaction and its response to vasodilation. METHODS: Nifedipine, a calcium channel blocker, vasodilator and systemic antihypertensive agent improves visual fields in NTG patients following acute and chronic dosing. The effect of 60 mg of daily orally administered nifedipine on OPA, intraocular pressure (IOP, German abbreviation: IOD), blood pressure (BP, German abbreviation: RR) and pulse rate (PR, German abbreviation: HF) were measured prior to and for 3 months after initiating nifedipine therapy in 32 NTG patients with and without a vasospastic reaction as manifested by a local cold exposure test. Before treatment, all patients had reduced OPA evaluated with the Langham Ocular Blood Flow System. RESULTS: During nifedipine treatment NTG patients with a vasospastic reaction showed a significant (p < 0.001) increase in OPA, whereas NTG patients without a vasospastic reaction showed no sig. (p > 0.05) change in OPA. CONCLUSION: There may be two different subgroups of NTG patients, those who have a vasospastic reaction and react to nifedipine, while others lack the ability to react to nifedipine or might have a different, non-vasospastic pathology. Calcium channel blockers and other vasodilators may be useful in the treatment of vasospastic NTG patients.

Administration, Oral↗
PubMed1997

The mechanism of intraocular pressure rise during cyclocryotherapy.

PURPOSE: Intraocular pressure (IOP) spikes that occur during cyclocryotherapy for advanced glaucoma may further injure the already damaged glaucomatous optic nerve and be responsible for visual impairment that may occur after this treatment. The authors investigated the mechanism of pressure rise to see whether it can be avoided and thus prevent further optic nerve injury. The authors postulated that intraocular ice forms during the cryo procedure and causes the pressure changes. METHODS: Intraocular pressure was monitored using a pneumatonometer during 15 cryocycles of four patients with advanced glaucoma and 21 cryocycles of five normal rabbits. A simple thermal model was developed to analyze the relation between volume expansion and pressure rise in the eye. The physical effect of freezing rabbit eye structures was investigated in vitro. RESULTS: The largest pressure spikes observed during the cryocycles in this work were increases of 32 mm Hg for humans and 25 mm Hg for rabbits. The mean value of the IOP immediately before and after the cryo freezing stage was 53 +/- 1 and 68 +/- 2 mm Hg, respectively, for humans and 22 +/- 1 and 32 +/- 1 mm Hg for rabbits. The parameters of the thermal model were determined from the observed IOP spikes. Calculated thaw times were consistent with measured times for return to precryo IOPs. In vitro cryoapplication (rabbit eye) showed the formation of an ice ball internal to the eye. CONCLUSIONS: Volumetric increase of the intraocular content related to the formation of an ice ball in the eye, is the mechanism of pressure spikes during cyclocryotherapy. Because this complication is unavoidable, other cyclodestuctive methods may be more prudent, particularly in patients with advanced glaucoma.

Animals↗
PubMed1996

Effect of oral nifedipine on ocular blood flow in patients with low tension glaucoma.

AIM: To investigate the effect of oral nifedipine on ocular blood flow in patients with low tension glaucoma (LTG). METHODS: In this prospective study we examined the effects of 3 weeks of treatment with oral nifedipine 30 mg/day in 11 patients with LTG, by using colour Doppler ultrasound imaging to measure haemodynamic variables in the central retinal (CRA), short posterior ciliary (SPCA), and ophthalmic (OA) arteries. Intraocular pressure (IOP) and blood pressures were also evaluated. RESULTS: Nifedipine failed to alter IOP nor did it change peak systolic velocity, end diastolic velocity,or the resistance index in any of the three ocular vessels studied (p > 0.05). However systolic and diastolic systemic arterial blood pressure measurements varied significantly after nifedipine treatment compared with baseline (p < 0.05). CONCLUSION: Our study failed to demonstrate a significant effect of nifedipine on retrobulbar circulation of patients with LTG.

Administration, Oral↗
PubMed1995

Nitric oxide synthase inhibitors protect rat retina against ischemic injury.

Elevation of the ocular pressure in the anterior chamber of the rat eye caused major ischemic damage, manifested as changes in retinal morphology. The two most affected structures were the inner plexiform layer, which decreased in thickness by 90%, and the number of ganglion cells, which decreased by 80%. Pretreatment of the animals with N omega-nitro-L-arginine, a nitric oxide (NOS) inhibitor, almost completely abolished the ischemic damage. Administration of aminoguanidine, a NOS inhibitor selective for the inducible enzyme, partially abolished the ischemic damage. Moreover, administration of the NOS inhibitors 1 h after ischemia, also protected the retina from damage, suggesting that similarly acting drugs could be used clinically to limit ischemic injury in humans. We conclude that NOS, and therefore NO, may be involved in the mechanism of ischemic injury to the retina.

Animals↗