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Biomedical subjects

A Karma

Publications and source records attributed to A Karma.

At least 37 records · Page 2Linked to original sources
PubMed2000

HLA-B27 typing in the categorisation of uveitis in a HLA-B27 rich population.

AIMS: To determine whether HLA-B27 typing helps the clinician in the diagnostic examination of uveitis in a HLA-B27 rich population and also whether the clinical picture of HLA-B27 positive unilateral acute or recurrent anterior uveitis (AAU) is distinguishable from the idiopathic negative form. METHODS: During a 3 year period 220 consecutive patients with undetermined uveitis at onset were examined in the Helsinki University Eye Clinic. HLA-B27 antigen was tested for 85% of the patients. Other laboratory or x ray examinations were performed on the basis of the anatomical classification of uveitis and the biomicroscopic features characteristic of uveitis associated systemic diseases. RESULTS: HLA-B27 antigen was found significantly more often in patients with anterior (71%) and acute/recurrent unilateral (79%) uveitis than in patients with intermediate, posterior panuveitis (7%), and chronic (7%) or bilateral (12%) forms. Of the 16 cases of HLA-B27 negative unilateral AAU, five showed biomicroscopic features representing uveitis entities. The remaining 11 cases did not differ in any respect from the cases of HLA-B27 positive unilateral AAU. CONCLUSION: HLA-B27 antigen helps the clinician in the diagnostic examination of unilateral AAU. Positive test results serve as a clue to search for spondyloarthropathies, and negative results indicate the need to look for specific uveitis entities and other systemic diseases. The occurrence of HLA-B27 positivity in conjunction with uveitis entities other than unilateral AAU is of the same level or less than in the population of Finland in general.

Acute Disease↗
PubMed1999

The laboratory diagnosis of ocular Lyme borreliosis.

BACKGROUND: A study was carried out to evaluate indirect enzyme-linked immunosorbent assay (ELISA), immunoblot analysis, and polymerase chain reaction (PCR) in the diagnostic work-up of ocular Lyme borreliosis. METHODS: Twenty patients with ocular Lyme borreliosis were examined. IgG and IgM antibodies to Borrelia burgdorferi were measured by ELISA in serum, and in cerebrospinal fluid (CSF) when indicated, and immunoblot analysis of B. burgdorferi IgG antibodies in serum was performed. A nested PCR was used to detect a segment of a gene coding for B. burgdorferi endoflagellin. The samples used in PCR testing were serum and CSF and in isolated cases conjunctiva and vitreous. RESULTS: Seventeen patients had elevated Borrelia antibodies in serum or CSF by ELISA. Seven patients, including two with negative ELISA, had a positive immunoblot. Seven of the 13 patients in whom PCR was examined during clinically active disease had a positive PCR result. Immunoblot analysis gave a negative result from the sera of five PCR-positive patients. CONCLUSIONS: For efficient diagnosis of ocular Lyme borreliosis, immunoblot analysis and PCR should be used in addition to ELISA. A positive PCR seems to be associated with a negative immunoblot.

Adolescent↗
PubMed1999

Phase-field model of dendritic sidebranching with thermal noise.

We investigate dendritic sidebranching during crystal growth in an undercooled melt by simulation of a phase-field model which incorporates thermal noise of microscopic origin. As a nontrivial quantitative test of this model, we first show that the simulated fluctuation spectrum of a one-dimensional interface in thermal equilibrium agrees with the exact sharp-interface spectrum up to an irrelevant short-wavelength cutoff comparable to the interface thickness. Simulations of dendritic growth are then carried out in two dimensions to compute sidebranching characteristics (root-mean-square amplitude and sidebranch spacing) as a function of distance behind the tip. These quantities are compared quantitatively to the predictions of the existing linear WKB theory of noise amplification. The extension of this study to three dimensions remains needed to determine the origin of noise in experiments.

Journal Article↗
PubMed1999

Theory of spiral wave dynamics in weakly excitable media: asymptotic reduction to a kinematic model and applications.

In a weakly excitable medium, characterized by a large threshold stimulus, the free end of an isolated broken plane wave (wave tip) can either rotate (steadily or unsteadily) around a large excitable core, thereby producing a spiral pattern, or retract, causing the wave to vanish at boundaries. An asymptotic analysis of spiral motion and retraction is carried out in this weakly excitable large core regime starting from the free-boundary limit of the reaction-diffusion models, valid when the excited region is delimited by a thin interface. The wave description is shown to naturally split between the tip region and a far region that are smoothly matched on an intermediate scale. This separation allows us to rigorously derive an equation of motion for the wave tip, with the large scale motion of the spiral wave front slaved to the tip. This kinematic description provides both a physical picture and exact predictions for a wide range of wave behavior, including (i) steady rotation (frequency and core radius), (ii) exact treatment of the meandering instability in the free-boundary limit with the prediction that the frequency of unstable motion is half the primary steady frequency, (iii) drift under external actions (external field with application to axisymmetric scroll ring motion in three dimensions, and spatial- or/and time-dependent variation of excitability), and (iv) the dynamics of multiarmed spiral waves with the prediction that steadily rotating waves with two or more arms are linearly unstable. Numerical simulations of FitzHugh-Nagumo kinetics are used to test several aspects of our results. In addition, we discuss the semiquantitative extension of this theory to finite cores and pinpoint mathematical subtleties related to the thin interface limit of singly diffusive reaction-diffusion models.

Journal Article↗
PubMed1999

Eutectic colony formation: a stability analysis.

Experiments have widely shown that a steady-state lamellar eutectic solidification front is destabilized on a scale much larger than the lamellar spacing by the rejection of a dilute ternary impurity and forms two-phase cells commonly referred to as "eutectic colonies." We extend the stability analysis of Datye and Langer [V. Datye and J. S. Langer, Phys. Rev. B 24, 4155 (1981)] for a binary eutectic to include the effect of a ternary impurity. We find that the expressions for the critical onset velocity and morphological instability wavelength are analogous to those for the classic Mullins-Sekerka instability of a monophase planar interface, albeit with an effective surface tension that depends on the geometry of the lamellar interface and, nontrivially, on interlamellar diffusion. A qualitatively new aspect of this instability is the occurrence of oscillatory modes due to the interplay between the destabilizing effect of the ternary impurity and the dynamical feedback of the local change in lamellar spacing on the front motion. In a transient regime, these modes lead to the formation of large scale oscillatory microstructures for which there is recent experimental evidence in a transparent organic system. Moreover, it is shown that the eutectic front dynamics on a scale larger than the lamellar spacing can be formulated as an effective monophase interface free boundary problem with a modified Gibbs-Thomson condition that is coupled to a slow evolution equation for the lamellar spacing. This formulation provides additional physical insights into the nature of the instability and a simple means to calculate an approximate stability spectrum. Finally, we investigate the influence of the ternary impurity on a short wavelength oscillatory instability that is already present at off-eutectic compositions in binary eutectics.

Journal Article↗
PubMed1997

The etiology of uveitis: the role of infections with special reference to Lyme borreliosis.

PURPOSE: To assess the distribution of different uveitis entities and to evaluate their associations with infections, especially Lyme borreliosis. METHODS: During a one-year period 160 consecutive uveitis patients were evaluated in a university clinic. Selected tests were performed depending on the medical history of the patient and the clinical picture of the ocular inflammation. RESULTS: Uveitis was classified into selected entities for 74.4% of the patients. A direct infection was suggested to be linked with uveitis in 23 patients (14.4%). Lyme borreliosis, toxoplasmosis, and herpetic infections were the most frequently seen, in seven patients (4.3%) each. All patients with Lyme uveitis had manifestations of the posterior segment of the eye, such as vitritis, retinal vasculitis, neuroretinitis, chorioretinitis, or optic neuropathy. CONCLUSION: Infections are an important cause of uveitis in a university clinic. Lyme borreliosis is a newly recognised uveitis entity which should be kept in mind in the differential diagnosis of intermediate or posterior uveitis in areas endemic for Lyme borreliosis.

Adolescent↗
PubMed1996

Long-term follow-up of chronic Lyme neuroretinitis.

PURPOSE: The authors report sequential fluorescein angiographic and color photographic findings of the fundi and response to treatment in a patient with chronic Lyme neuroretinitis. METHODS: A Lyme enzyme-linked immunosorbent assay with purified 41-kd flagellin as antigen was used to detect immunoglobulin G and immunoglobulin M antibodies to Borrelia burgdorferi in serum, cerebrospinal fluid, and vitreous. The changes were documented by fluorescein angiography and color photography tests performed during a 5 1/2 year follow-up. RESULTS: The diagnosis of Lyme neuroretinitis was based on the history of erythema migrans and positive Lyme enzyme-linked immunosorbent assay tests from cerebrospinal fluid and vitreous and by the exclusion of other infectious and systemic diseases and uveitis entities. Fluorescein angiography results disclosed bilateral chronic neuroretinal edema with areas of cystoid, patchy, and diffuse hyperfluorescence peripapillary and in the macular areas. The hyperfluorescent lesions enlarged despite a 9-month period of antibiotic therapy. CONCLUSION: Lyme borreliosis may cause neuroretinitis with unusual angiographic findings. Chronic Lyme neuroretinitis may be unresponsive to antibiotic therapy.

Adult↗
PubMed1996

Ocular manifestations and treatment of Lyme disease.

Ocular manifestations in Lyme disease have been considered rare. In surveys and epidemiologic studies the possibility of ocular Lyme disease has usually not been taken into account. Patients with late ocular. Lyme disease may be seronegative by routine enzyme-linked immunosorbent assays, but immunoblot or detection of Borrelia DNA by polymerase chain reaction may help in diagnosing those cases. An ophthalmologist may suspect the diagnosis of Lyme disease in inflammatory ocular syndromes with unusual biomicroscopic or angiographic findings. Intraocular Lyme disease is usually treated with intravenous ceftriaxone or cefotaxime. Jarisch-Herxheimer reaction may occasionally complicate the antibiotic treatment of ocular manifestations. Overtreatment with ceftriaxone should be avoided because of a possibility of biliary complications.

Eye Diseases↗
PubMed1996

Screening of amblyopic children and long-term follow-up.

A prospective study of amblyopic children was carried out in 1982-1992 in the ophthalmology unit of a community health center, a referral center for 14,000 preschool children. Five hundred and twenty-six children in 1982-1983 were referred to an ophthalmologist because of a suspicion of amblyopia, strabismus or other visual disorders. Amblyopia was diagnosed in 109 children. In 18 children amblyopia was on an organic basis and among them 4 children had X-chromosomal retinoschisis. Risk factors for functional amblyopia were convergent strabismus, spherical equivalent of the refractive error of 3.5 dioptres or more or anisometropia of 1.0 dioptres or more. The children with established functional amblyopia (91 children) were treated with a full-time occlusion, or, at the age of younger than 18 months, with 0.5% atropin, and, at the minimum of 6 years, with pleoptics when indicated. One hundred amblyopic children were followed for a minimum of 4 years, reinstituting the occlusion therapy if visual acuity deteriorated. Seventy-two children with functional amblyopia (79%) were available for a detailed ophthalmological examination 9.7 years, on the average, after the initial examination. Only three of these children (4%) had visual acuity of less than 0.4 at that time. Well-functioning child health centers and school health care, as well as the availability of ophthalmological services, are important for a good final visual result of amblyopic children.

Amblyopia↗
PubMed1995

Diagnosis and clinical characteristics of ocular Lyme borreliosis.

PURPOSE: To establish a diagnosis, in a group of patients we studied the characteristics of ocular Lyme borreliosis. METHODS: During a two-year period, 236 patients with prolonged external ocular inflammation, uveitis, retinitis, optic neuritis, or unexplained neuro-ophthalmic symptoms were examined for Lyme borreliosis. Antibodies to Borrelia burgdorferi were measured by indirect ELISA and western blot. Cerebrospinal fluid was also analyzed by polymerase chain reaction. RESULTS: Ocular Lyme borreliosis was diagnosed in ten patients on the basis of medical history, clinical findings, and serologic test results. Results of ELISA disclosed that five patients were seropositive, two patients showed borderline reactivity, and three patients were seronegative. Four of the five patients with borderline or negative results by ELISA had a positive result by western blot analysis. In one seropositive patient, polymerase chain reaction verified a gene of B. burgdorferi endoflagellin from the vitreous and cerebrospinal fluid specimen. In five of the six patients with known onset of the Borrelia infection, the ocular disorder appeared as a late manifestation. Abnormalities of the posterior segment of the eye, such as vitreitis, retinal vasculitis, neuroretinitis, choroiditis, and optic neuropathy were seen in six patients. Bilateral paralytic mydriasis, interstitial keratitis, episcleritis, and anterior uveitis were seen in one patient each. CONCLUSIONS: Late-phase ocular Lyme borreliosis is probably underdiagnosed because of weak seropositivity or seronegativity in ELISA assays. Ocular borrelial manifestations show characteristics resembling those seen in syphilis.

Adolescent↗