REACTION OF THE RABBIT CORNEAL ENDOTHELIUM TO NYLON SUTURES - A SEM STUDY

Nylon and stainless steel sutures separately placed deeply into rabbit corneas by splitting the stroma for a few millimeters, without closing sutures, remained in the cornea for two, four and six weeks respectively. In contrast to the stainless steel sutures an extensive tissue reaction could be observed clinically around the nylon sutures within a few days and was still present after 4-6 weeks. On the endothelial side, covering of the nylon with fibroblast cells took place very slowly, this in contrast with stainless steel. Irritation of the tissue and an oedematous appearance of the endothelium around the nylon suture was the result. At first a kind of collagen network, often mixed with inflammatory cells, was deposited on the nylon material before fibroblast cells could grow in. Covering of the stainless steel started quite soon after implantation, without preliminary deposition of collagen material. The reason for this phenomenon must be sought in the high free surface energy of the stainless steel, which attracts cells, in contrast to nylon which has a very low free surface energy

A demographic approach to the assessment of Downs syndrome screening performance

The aim of this article is to examine the performance of screening for fetal Down syndrome (DS) in the context of demographic variation in time and place, using population and fertility data for several European countries. Two screening approaches are distinguished: one on the basis of maternal serum screening with human chorionic gonadotropin (hCG) and alpha-fetoprotein (AFP) in combination with maternal age, and one on the basis of maternal age only. Screening performance, as measured by detection and false-positive ratios, is shown to be the result of the screening approach chosen and of the demographic characteristics of the population under consideration. A proper distinction between these two determinants of DS screening performance should be made, in order to distinguish between an improvement in screening performance that is brought about by a new screening approach and an improvement that is brought about by demographic change. We recommend that measures of DS screening performance be standardized for demographic variation. The methodology and demographic data presented in this article can be used for this purpose. (C) 1997 by John Wiley & Sons, Ltd