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

Does the mind map learning strategy facilitate information retrieval and critical thinking in medical students?

<p>Abstract</p> <p>Background</p> <p>A learning strategy underutilized in medical education is mind mapping. Mind maps are multi-sensory tools that may help medical students organize, integrate, and retain information. Recent work suggests that using mind mapping as a note-taking strategy facilitates critical thinking. The purpose of this study was to investigate whether a relationship existed between mind mapping and critical thinking, as measured by the Health Sciences Reasoning Test (HSRT), and whether a relationship existed between mind mapping and recall of domain-based information.</p> <p>Methods</p> <p>In this quasi-experimental study, 131 first-year medical students were randomly assigned to a standard note-taking (SNT) group or mind map (MM) group during orientation. Subjects were given a demographic survey and pre-HSRT. They were then given an unfamiliar text passage, a pre-quiz based upon the passage, and a 30-minute break, during which time subjects in the MM group were given a presentation on mind mapping. After the break, subjects were given the same passage and wrote notes based on their group (SNT or MM) assignment. A post-quiz based upon the passage was administered, followed by a post-HSRT. Differences in mean pre- and post-quiz scores between groups were analyzed using independent samples <it>t</it>-tests, whereas differences in mean pre- and post-HSRT total scores and subscores between groups were analyzed using ANOVA. Mind map depth was assessed using the Mind Map Assessment Rubric (MMAR).</p> <p>Results</p> <p>There were no significant differences in mean scores on both the pre- and post-quizzes between note-taking groups. And, no significant differences were found between pre- and post-HSRT mean total scores and subscores.</p> <p>Conclusions</p> <p>Although mind mapping was not found to increase short-term recall of domain-based information or critical thinking compared to SNT, a brief introduction to mind mapping allowed novice MM subjects to perform similarly to SNT subjects. This demonstrates that medical students using mind maps can successfully retrieve information in the short term, and does not put them at a disadvantage compared to SNT students. Future studies should explore longitudinal effects of mind-map proficiency training on both short- and long-term information retrieval and critical thinking.</p

Correlation between Local Stress and Strain and Lamina Cribrosa Connective Tissue Volume Fraction in Normal Monkey Eyes

Biomechanical finite element models of the connective tissues of the ONH that incorporate detailed descriptions of individual variation lamina cribrosa microarchitecture were generated for four pairs of bilaterally normal monkey eyes. The bilateral similarity in mechanical response and its dependence on the intrinsic material properties of the lamina cribrosa were explored by analyzing laminar displacement, strain, and stress and their relationship to the underlying microarchitecture