Analysis of best corrected visual acuity following corneal refractive surgery comparing low and standard predicted postoperative keratometry

BACKGROUND: It is a commonly held view in the ophthalmologic community that eyes with sufficiently low calculated postoperative corneal keratometry, less than 35 diopters, should not undergo corrective refractive laser surgery (CRLS) due to the increased risk of best corrected visual acuity (BCVA) loss. Typical CRLS include Laser In-Situ Keratomileusis (LASIK), Photorefractive Keratectomy (PRK), and Laser-Assisted Sub-Epithelial Keratectomy (LASEK). Evidence for this claim in currently available literature is sparse and inconsistent. PURPOSE: To further elucidate the relationship between calculated “flat” postoperative corneal keratometry and loss of BCVA. Additionally, to investigate the role of procedure type (LASIK, ASA, or LASEK) and degree of calculated postoperative corneal flatness on visual outcomes following CRLS. METHODS: 222 eyes (111 candidates and 111 controls) were retrospectively analyzed and matched based on calculated postoperative keratometry compared to control subgroups with calculated postoperative keratometries ≥38 D and further stratified into subgroups 1b (K=38-38.99 D), 2b (K=39-39.99 D), 3b (K=40-40.9 9D), and 4b (K≥41 D). All of the eyes had undergone LASIK, PRK, or LASEK between December 2008 and November 2016 at Boston Eye Group/Boston Laser in Brookline, MA. RESULTS: Statistical analyses showed no significant differences between candidates and controls in preoperative BCVA (p=0.650) and postoperative BCVA (p=0.081). Subgroup matching showed no significant differences in the amount of tissue ablated in 1a & 1b (p=0.946), 2a & 2b (p=0.694), 3a & 3b (p=0.989), and 4a & 4b (p=0.986). There was also no significant change between preoperative and postoperative BCVA in subgroups 1a (p=0.367), 2a (p=0.297), 3a (p=0.576), 4a (p=0.669), 1b (p=0.458), 2b (p=0.227), 3b (p=0.071), or 4b (p=0.703). 3 of 111 (2.70%) candidate eyes and 1 (0.90%) control eye lost 1+ lines of BCVA following surgery. There was no statistical difference in 1+ lines of BCVA lost between these groups (p=0.313). Similarly, the type of CRLS undergone did not affect the rate of BCVA line loss (p=0.793). CONCLUSION: Our evidence suggests that in a matched comparison of flat and normal mathematically predicted postoperative keratometries, there was no increase in BCVA lost due to flat keratometry

Development of design data for graphite reinforced epoxy and polyimide composites

Processing techniques and design data were characterized for a graphite/epoxy composite system that is useful from 75 K to 450 K, and a graphite/polyimide composite system that is useful from 75 K to 589 K. The Monsanto 710 polyimide resin was selected as the resin to be characterized and used with the graphite fiber reinforcement. Material was purchased using the prepreg specification for the design data generation for both the HT-S/710 and HM-S/710 graphite/polyimide composite system. Lamina and laminate properties were determined at 75 K, 297 K, and 589 K. The test results obtained on the skin-stringer components proved that graphite/polyimide composites can be reliably designed and analyzed much like graphite/epoxy composites. The design data generated in the program includes the standard static mechanical properties, biaxial strain data, creep, fatigue, aging, and thick laminate data

Painting Supports: Significance, Historical Review, Types and Appropriate Preparations for Effective Painting

Paintings tend to appeal to many art lovers due to their colourful schemes, emotional expressiveness, and aesthetic attractions, among others. Additionally, they are comparatively less cumbersome to produce with easy-to-obtain tools and materials; and also, have expansive possibilities for diverse styles and techniques pliable on almost any available surface. However, one important factor that gives them solid foundations for durability and longer lifespan, and to which many painters fail to attach much attention, is the surfaces on which paintings are executed. Through observation, it is established that most painting supports in Ghana are restricted to canvas making them monotonous, less exploratory and markedly limited in pursuit of individual artistic talents. Interviews conducted with some selected painters in Ghana suggest insufficient knowledge about diversified painting surfaces and their appropriate paint systems. This paper explores into the importance of painting supports, their historical antecedents, types, surface treatments, and relative paint mediums. It explains the advantages of various painting supports and their techniques to facilitate the acquisition of knowledge and skills needed to diversify their usage in Ghana. Keywords: Painting Support, Paint system, Grounding, Paint Medium, Ke

Smallholder Participation in Agricultural Value Chains: Comparative Evidence from Three Continents

Supermarkets, specialized wholesalers, and processors and agro-exporters’ agricultural value chains have begun to transform the marketing channels into which smallholder farmers sell produce in low-income economies. We develop a conceptual framework through which to study contracting between smallholders and a commodity-processing firm. We then conduct an empirical meta-analysis of agricultural value chains in five countries across three continents (Ghana, India, Madagascar, Mozambique, and Nicaragua). We document patterns of participation, the welfare gains associated with participation, reasons for non-participation, the significant extent of contract non-compliance, and the considerable dynamism of these value chains, as farmers and firms enter and exit frequently.

Human prenatal progenitors for pediatric cardiovascular tissue engineering

Pediatric cardiovascular tissue engineering is a promising strategy to overcome the lack of autologous, growing replacements for the early repair of congenital malformations in order to prevent secondary damage to the immature heart. Therefore, cells should be harvested during pregnancy as soon as the cardiovascular defect is detected enabling the generation of living autologous implants with the potential of growth, remodeling and regeneration ready to use at or shortly after birth. Furthermore, the ideal cell source should be easily accessible and allow cell harvest without substantial risks for both the mother and the child and without sacrifice of intact infantile donor tissue. In this work, human prenatal progenitor cells obtained from different extra-embryonically situated fetal tissues were investigated with regard to the pediatric cardiovascular tissue engineering concept. In individual studies prenatal progenitor cells were isolated from different fetal tissues including umbilical cord blood and cord tissue, chorionic villi and amniotic fluid. Cells were expanded and differentiated into cell types that are required for cardiovascular replacements in order to match the characteristics of their native counterparts: a myofibroblast-fibroblast-like cell type producing extracellular matrix and an endothelial cell type forming an antithromobogenic and blood-compatible surface. Thereby, cell phenotypes were analyzed by flowcytometry and immunohistochemistry and genotypes were determined. For the fabrication of cardiovascular tissues, biodegradable cardiovascular scaffolds (PGA/P4HB) were seeded with fibroblast-myofibroblast-like cells derived from either umbilical cord tissue, chorionic villi or amniotic fluid. Constructs were implanted in an in vitro pulse duplicator and exposed to biochemical and/or mechanical stimulation. After, in vitro maturation time, the surfaces of cardiovascular constructs were endothelialized with differentiated umbilical cord blood-derived endothelial progenitor cells or amniotic fluid-derived endothelial progenitor cells and conditioned for an additional 7d. Analysis of the neo-tissues comprised histology, immunohistochemistry (vimentin, a- SMA, desmin, Ki-67), biochemistry (extracellular matrix (ECM) - analysis, DNA), mechanical testing and scanning electron microscopy (SEM). Neo-endothelia were analysed by immunohistochemistry (CD31, vWF, thrombomodulin, tissue factor, eNOS). After differentiation, cells demonstrated characteristics of fibroblast-myofibroblast-like cells expressing vimentin, desmin and partly a-SMA independent of the cell source. Furthermore, umbilical cord blood-derived endothelial progenitor cells and amniotic fluid-derived cells expressed typical endothelial cell markers such as CD31, vWF, thrombomodulin, tissue factor, and eNOS, respectively. Genotyping confirmed the fetal origin of the cells without contamination with maternal cells. All cardiovascular constructs showed cellular tissue formation with functional endothelia as indicated by the expression of eNOS. Expression of Ki-67 confirmed proliferation of cells in all parts of the neo-tissues. Matrix analysis (collagen and proteoglycans) and DNA content demonstrated constituents typical of native cardiovascular tissues. Mechanical properties revealed native analogous profiles but did not reach native values. SEM showed cell-ingrowth into the polymer and smooth surfaces covered densely with endothelial cells. Prenatal progenitors from different sources were successfully used for the in vitro fabrication and maturation of living autologous cardiovascular constructs. With regard to clinical application the use of amniotic fluid-derived prenatal progenitor cells represents the most attractive approach as it enables the prenatal fabrication of cardiovascular replacements based on a single cell source ready to use at birth

Smallholder Participation in Agricultural Value Chains: Comparative Evidence from Three Continents

Supermarkets, specialized wholesalers, and processors and agro-exporters’ agricultural value chains have begun to transform the marketing channels into which smallholder farmers sell produce in low-income economies. We develop a conceptual framework through which to study contracting between smallholders and a commodity-processing firm. We then conduct an empirical meta-analysis of agricultural value chains in five countries across three continents (Ghana, India, Madagascar, Mozambique, and Nicaragua). We document patterns of participation, the welfare gains associated with participation, reasons for non-participation, the significant extent of contract non-compliance, and the considerable dynamism of these value chains, as farmers and firms enter and exit frequently.Agricultural Value Chains, Contract Farming, Africa, Asia, Latin America

Investigation of waste management practices and cleaner production application in a tannery : case study

This research study investigated ways of rationalizing chemical water and energy consumption usage and reducing waste discharge in a tannery. The work was motivated by the need to achieve sustainable development through the use of best practices to achieve compliance with environmental regulations through the application of Cleaner Production initiatives. The processes involved stripping of over 70% of animal skin wet mass, to retain a refined product. It is this non-useable material which is contaminated with process chemicals that is a cause for environmental concern. Effort was made to explore areas that consumed the most resources, and had the most emissions, with a view to recover, reuse and recycle or substitute waste material generated in the tannery