Viscoelastic material properties of the peripapillary sclera in normal and early-glaucoma monkey eyes

PURPOSE. To test the hypothesis that changes in the viscoelastic material properties of peripapillary sclera are present within monkey eyes at the onset of early experimental glaucoma detected by confocal scanning laser tomography (CSLT). METHODS. Short-term (3-9 weeks), moderate (Յ44 mm Hg) intraocular pressure (IOP) elevation was induced in one eye of each of eight male monkeys by lasering the trabecular meshwork. This procedure generated early experimental glaucoma, defined as the onset of CSLT-detected optic nerve head (ONH) surface change, in the treated eye. Scleral tensile specimens from the superior and inferior quadrants of the eight earlyglaucoma eyes were subjected to uniaxial stress relaxation and tensile tests to failure and the results compared with similar data obtained in a previous study of 12 normal (nonglaucomatous) eyes. Linear viscoelastic theory was used to characterize viscoelastic material property parameters for each specimen. Differences in each parameter due to quadrant and treatment were assessed by analysis of variance (ANOVA). RESULTS. Peripapillary sclera from the early-glaucoma eyes exhibited an equilibrium modulus (7.46 Ϯ 1.58 MPa) that was significantly greater than that measured in normal eyes (4.94 Ϯ 1.22 MPa; mean Ϯ 95% confidence interval, P Ͻ 0.01, ANOVA). Quadrant differences were not significant for the viscoelastic parameters within each treatment group. CONCLUSIONS. The long-term viscoelastic material properties of monkey peripapillary sclera are altered by exposure to moderate, short-term, chronic IOP elevations and these alterations are present at the onset of CSLT-detected glaucomatous damage to the ONH. Damage to and/or remodeling of the extracellular matrix of these tissues may underlie these changes in scleral material properties. (Invest Ophthalmol Vis Sci. 2005;46: 540 -546 1 The finite element method is a computer-based engineering technique that estimates the stresses (force/cross-sectional area) and strains (local deformation under those stresses) within a complex load-bearing structure. 2 The important aspects of a finite element model are the three-dimensional geometry and material properties of the load-bearing structure and the appropriate boundary and mechanical loading conditions. 2 Within such models of the monkey ONH, scleral material properties are needed to characterize accurately the important transition between the peripapillary sclera and the peripheral laminar beams. To characterize the material properties of peripapillary sclera, we constructed a controlled-environment testing apparatus capable of performing uniaxial biomechanical testing of soft tissues in tension. The overall response of a tissue to a load is the combination of instantaneous (elastic) and time-dependent (viscous) responses, which are governed by its viscoelastic material properties. All soft tissues are viscoelastic, and the characterization of the instantaneous and time-dependent aspects of these material properties is important in understanding a tissue's behavior as a load-bearing structure and its response to short-and long-term changes in the applied load. Accurate characterization of a tissue's material properties can lead to a broader understanding of the mechanisms that underlie tissue damage, as well as determine the resultant altered load-bearing behavior of a remodeled or healed tissue. In a previous report we performed quadrant-based uniaxial tensile testing of peripapillary sclera from normal rabbit and normal monkey eyes 3 and found no differences in the viscoelastic material properties of the peripapillary sclera by quadrant (superior, inferior, nasal, and temporal to the ONH) in either species. In addition, when normal rabbit and monkey sclera were compared with one another, peripapillary sclera from monkey eyes was stiffer and showed slower stress relaxation than sclera from rabbit eyes. The present study tests the hypothesis that changes in the viscoelastic material properties of monkey peripapillary sclera are present at the earliest detectable stage of glaucomatous damage to the ONH, defined as the onset of confocal scanning laser tomography (CSLT)-detected ONH surface change. MATERIALS AND METHODS Animals, Scleral Specimens, and Study Design All animals were treated in accordance with the ARVO Statement for the Use of Animals in Ophthalmic and Vision Research. In the present study, a single scleral tensile specimen was generated from either the superior or inferior quadrant of eight eyes with experimental early glaucoma, yielding four early-glaucoma specimens for each quadrant. Each specimen underwent a multistage uniaxial tensile test. ViscoelasFrom th

On the origin of the O and B-type stars with high velocities II Runaway stars and pulsars ejected from the nearby young stellar groups

We use milli-arcsecond accuracy astrometry (proper motions and parallaxes) from Hipparcos and from radio observations to retrace the orbits of 56 runaway stars and nine compact objects with distances less than 700 pc, to identify the parent stellar group. It is possible to deduce the specific formation scenario with near certainty for two cases. (i) We find that the runaway star zeta Ophiuchi and the pulsar PSR J1932+1059 originated about 1 Myr ago in a supernova explosion in a binary in the Upper Scorpius subgroup of the Sco OB2 association. The pulsar received a kick velocity of about 350 km/s in this event, which dissociated the binary, and gave zeta Oph its large space velocity. (ii) Blaauw & Morgan and Gies & Bolton already postulated a common origin for the runaway-pair AE Aur and mu Col, possibly involving the massive highly-eccentric binary iota Ori, based on their equal and opposite velocities. We demonstrate that these three objects indeed occupied a very small volume \sim 2.5Myr ago, and show that they were ejected from the nascent Trapezium cluster. We identify the parent group for two more pulsars: both likely originate in the 50 Myr old association Per OB3, which contains the open cluster alpha Persei. At least 21 of the 56 runaway stars in our sample can be linked to the nearby associations and young open clusters. These include the classical runaways 53 Arietis (Ori OB1), xi Persei (Per OB2), and lambda Cephei (Cep OB3), and fifteen new identifications, amongst which a pair of stars running away in opposite directions from the region containing the lambda Ori cluster. Other currently nearby runaways and pulsars originated beyond 700 pc, where our knowledge of the parent groups is very incomplete.Comment: Accepted for publication in the A&A. 29 pages, 19 figure

DPOAEs in Children With Sickle Cell Disease

The purpose of this study was to investigate distortion product otoacoustic emissions (DPOAEs) in young normal-hearing children with sickle cell disease (SCD). It was hypothesized that the prevalence of DPOAEs and response amplitudes would be lower than those in children with normal hemoglobin due to suspected compromised cochlear function as a result of vaso-occlusive events characteristic of SCD. Twenty African-American children with SCD and 15 African-American children with normal hemoglobin participated. Distortion product OAEs were evoked by thirteen primary tone pairs with f2 frequencies ranging from 1000 to 4500 Hz. The primary tones were presented at and L1 and L2 levels of 70 and 60 dB SPL (high) and 50 and 40 dB SPL (low), respectively. The findings of this study were completely unexpected and contrary to our original hypotheses. The likelihood of detecting a DPOAE response was not related to the clinical status of the children. Distortion product OAE amplitudes were significantly larger for children with SCD (p = .01). Educational Objectives: After completing this article the reader will (1) have a basic knowledge of the audiometric complications of sickle cell disease and (2) appreciate the differences in DPOAEs between young normal-hearing children with sickle cell DPOAEs in Children With Sickle Cell Disease 3 disease and young normal-hearing children with normal hemoglobin

Variation of Laminar Depth in Normal Eyes With Age and Race

PURPOSE. To determine if laminar depth (LD) and prelaminar tissue volume (PTV) are associated with age and race in healthy human eyes. METHODS. Optic nerve head images from enhanced depth imaging spectral-domain optical coherence tomography of 166 normal eyes from 84 subjects of African descent (AD) and European descent (ED) were manually delineated to identify the principal surfaces: internal limiting membrane, Bruch's membrane (BM), anterior sclera (AS), and anterior surface of the lamina cribrosa. These four surfaces defined the LD and PTV using Bruch's membrane opening (BMO) and AS for reference structures. Generalized estimating equations were used to evaluate whether the effect of age on each outcome was differential by race. RESULTS. When age was analyzed as a continuous variable, the interaction term between age and race was statistically significant for mean LD BMO (P ¼ 0.015) and mean LD AS (P ¼ 0.0062) after adjusting for axial length and BMO area. For every 1-year increase in age, the LD AS was greater on average by 1.78 lm in AD subjects and less by 1.71 lm in ED subjects. Mean PTV was lower in the older subjects (1248 3 10 6 lm 3 AD, 881 3 10 6 lm 3 ED) compared to the younger subjects (1316 3 10 6 lm 3 AD, 1102 3 10 6 lm 3 ED) in both groups. CONCLUSIONS. With increasing age, the LD changes differently across racial groups in normal subjects. The LD in ED subjects showed a significantly decreasing slope suggesting that the lamina moves anteriorly with age in this group. Keywords: lamina cribrosa, laminar depth, spectral-domain optical coherence tomography I ndividuals of African descent (AD) have a higher prevalence of primary open-angle glaucoma with worse visual outcomes from the disease compared to those of European descent (ED). 1-5 Investigation into the many possible causes of this disparity reveals racial and ethnic differences in the anatomy of the optic nerve head (ONH). 3,6-14 Variation in ONH parameters, such as larger optic discs, deeper cups, and thicker overall retinal nerve fiber layer thicknesses in AD individuals

Hygiene and biosecurity: the language and politics of risk in an era of emerging infectious diseases

Infectious diseases, such as methicillin-resistant Staphylococcus aureus and avian influenza, have recently been high on the agenda of policy makers and the public. Although hygiene and biosecurity are preferred options for disease management, policy makers have become increasingly aware of the critical role that communication assumes in protecting people during outbreaks and epidemics. This article makes the case for a language-based approach to understanding the public perception of disease. Health language research carried out by the authors, based on metaphor analysis and corpus linguistics, has shown that concepts of journeys, pathways, thresholds, boundaries and barriers have emerged as principal framing devices used by stakeholders to advocate a hygiene based risk and disease management. These framings provide a common ground for debate, but lead to quite different perceptions and practices. This in turn might be a barrier to global disease management in a modern world

Longitudinal, epidemiologic studies of female reproductive aging

Human female reproductive aging consists of multiple processes and interacts with other physiological systems in unique ways. Here we discuss eight recent longitudinal, epidemiologic studies of female reproductive aging that include endocrine data to highlight their contributions to our understanding of these various aging processes and their interactions. Specifically, we review data on ovarian and nonovarian reproductive aging processes and reproductive staging. We consider these data in the context of longitudinal research design and research goals, identify limitations of the studies but also ways in which existing longitudinal data can further our understanding of aging processes, and make recommendations for future studies of female reproductive aging.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/79073/1/j.1749-6632.2010.05525.x.pd

Insights Into Elevated Distortion Product Otoacoustic Emissions In Sickle Cell Disease: Comparisons of Hydroxyurea-treated and Non-treated Young Children

Distortion product otoacoustic emissions (DPOAEs) were examined in 15 normal- hearing African-American children between the ages of 6 and 14 years with homozygous sickle cell disease (SCD), who were on a regimen of hydroxyurea (HDU), a drug that reduces inflammatory processes and symptoms of SCD; a matched group of 15 African- American children with homozygous SCD not on HDU; and 15 African-American children with normal hemoglobin. DPOAEs were evoked by 13 primary tone pairs with f2 frequencies ranging from 1000 to 4500 Hz. Increased DPOAE amplitudes, believed to be a precursor of eventual hearing loss, were evident in children with SCD who were not receiving HDU. Those taking HDU had DPOAE amplitudes similar to normal controls. These findings suggest that HDU, in addition to reducing symptoms of SCD, may play a role in inhibiting or preventing cochlear pathology and hearing loss in individuals with SCD. Key Words: distortion product otoacoustic emissions; sickle cell disease; hydroxyurea Abbreviations: ABR = auditory brainstem response; DPOAE = distortion product otoacoustic emission; HDU = hydroxyurea; HbSS = homozygous sickle cell disease; ICAM = intercellular adhesion molecule; M = mean; OAE = otoacoustic emission; p = probability; PECAM = platelet-endothelial cell adhesion molecule SCD = sickle cell disease; SD = standard deviation of the mean; SOAE = spontaneous otoacoustic emission; TEOAE = transient evoked otoacoustic emission; VCAM = vascular cell adhesion molecule