|Contact lenses are the thin lenses that are placed directly on the surface of the eye. They are medical devices used for the correction of eyesight. Contact lenses correct vision better as compared to conventional spectacles so they are preferred over spectacles. Contact lenses are made up of plastic polymer. Depending upon the type of lens the raw material differs. Like hard contact lenses are made of some variant of polymethyl methacrylate (PMMA) and soft contact lenses are made of a polymer such as poly hydroxyethyl methacrylate (pHEMA) which has hydrophilic qualities, means it can soak up water but still retain its shape and other optic functions.
The impact factor of journal provides quantitative assessment tool for grading, evaluating, sorting and comparing journals of similar kind. It reflects the average number of citations to recent articles published in science and social science journals in a particular year or period, and is frequently used as a proxy for the relative importance of a journal within its field. It is first devised by Eugene Garfield, the founder of the Institute for Scientific Information. The impact factor of a journal is evaluated by dividing the number of current year citations to the source items published in that journal during the previous two years.