ABSTRACT
Measurement bias (MB) has been described in causal structures but is still not entirely clear. In practice, the correctness of substitution estimate (SE) of effect is a prerequisite for causal inference, usually based on a bidirectionally non-differential misclassification between the measured exposure and the measured outcome. Based on a directed acyclic graph (DAG), this paper proposes a structure for the single-variable measure, where its MB is derived from the choice of an imperfect, "input/output device-like" measurement system. The MB of the SE is influenced both by the measurement system itself and by factors outside the measurement system: while the independence or dependence mechanism of the measurement system still ensures that the MB of the SE is bidirectionally non-differential; however, the misclassification can be bidirectionally non-differential, unidirectionally differential, or bidirectionally differential resulted from the factors outside the measurement system. In addition, reverse causality should be defined at the level of measurement, where measured exposures can influence measured outcomes and vice versa. Combined with temporal relationships, DAGs help elucidate MB's structures, mechanisms, and directionality.
Subject(s)
Humans , Confounding Factors, Epidemiologic , Data Interpretation, Statistical , Bias , CausalityABSTRACT
Background Our previous study determined that expressions of matrix metalloproteinases (MMPs) and tissue matrix metalloproteinase inhibitors (TIMPs)change in the conjuntival fibroblasts of conjunctivochalasis in vitro.To seek a suitable drug is very important in the prevention and treatment of conjunctivochalasis.Objective This study was to explore the effect of qijingmingmu soup on the expressions of MMPs and TIMPs in human conjunctival fibroblasts of conjunctivochalasis.Methods Twenty-four SD rats were randomized into two groups.Qijingmingmu soup was administration gastrically for consecutive 3 days,and normal saline solution was given in the same way in the control group.The blood was collected from aortaventralis and drug serum was prepared.Human conjunctival samples were obtained during the surgery of conjunctivochalasis relaxation and cultured in the DMEM containing 10％ fetal bovine serum,20％,15％,10％,5％ of drug serum and 8 ml/L epidermal growth factor(EGF) was added into the medium respectively.Enzyme-linked immunosorbent assay(ELISA)was used to detect the expressions of MMP1,MMP3,TIMP1 and TIMP3in conjunctival fibroblasts.Results Cultured cells grew well with the fusiform shape and showed the positive response for vimentin.The expression value of MMP1 (A value)in the cells was declined after administration of qijingmingmu soup.A significant difference was found in the expression of MMP1 among the control group,20％,15％,10％,5％ drug serum groups and EGF group(F=466.664,P＜0.05),and that in the 10％ ([9.92±0.14] mg/L) and 20％ ([11.87 ±0.11] mg/L) drug serum groups was significantly lowed in comparison with the control group([16.31±0.10] mg/L)(t=99.974,87.394,P＜0.05).The expression value of the MMP3in the cells in the various drug serum groups,EGF group and the control group was significantly different(F=158.168,P＜0.05),with a lower value in the 20％ drug serum group compared with the control group ([3.50±0.03] mg/L vs.[4.44 ± 0.11] mg/L) (t =21.991,P ＜ 0.05).Also,the significantly different expressing value of TIMP1 was seen among all the groups (F=183.508,P＜0.05),and expressing value of TIMP1 in the 15％ drug serum group was(1.88±0.06)mg/L,which was lower than(3.20±0.32) mg/L of the control group(t=10.353,P＜0.05).Furthermore,the expressing value of the TIMP3 in the cells was significantly different among the various groups(F=54.503,P＜0.05),and that of the 20％ drug serum group was (1.743±0.065)mg/L and it was significantly higher than (1.54 ± 0.05) mg/L of the control group (t =5.046,P =0.004).However,the expressing value of TIMP3of the 15％,10％ and 5％ drug serum groups was lower than that of the control group,respectively all at(P＜0.05).Conclusions Qijingmingmu soup drug serum at the concentration of 20％ can down-regulate the expressions of MMP1,MMP3,TIMP1 and up-regulate the expression of TIMP3 in human conjunctivochalasis bulbar conjunctival fibroblastsin vitro,which probably plays preventive and therapeutic effects on conjunctivochalasis.
ABSTRACT
Background Bulbar conjunctiva tissue appears to be thinning,elasticity declined,tension reduced and fascia atrophied in conjunctivochalasis.Histopathological examination of conjunctivochalasis shows decrease of elastic fibers and melt of collagen fibers.But there are fewer studies on the ultrastructure of conjunctiva of conjunctivochalasis up to now.Objective This study was to investigate the ultrastructure change of conjunctiva tissue in conjunctivochalasis.Methods Five loose conjunctiva samples of conjunctivochalasis and 5 normal conjunctival tissue samples were collected and ultra-microstructure changes of these samples were observed under the transmission electron microscope.Results The number of fibroblasts in conjunctivochalasis lamina was progressively decreased.The shape of fibroblasts was long and fusiform.Somatic synapse was slim.Nucleus-cytoplasm ratio was increased.Disorder,scattered and broken of the collagen fibril were seen,and some areas were dissolved or lacunae.Normal conjunctival fibroblasts were oval or polygonal,with wieners and long somatic synapse,and intercellular matrix was full of collagen fibril and dense arranged fibers.Fibroblasts in fascia of eonjunctivochalasis were linear,and collagen fibril was seriously defected.Fascia fibroblasts of normal bulbar conjunctiva were spindleshaped and bigger than conjunctivochalasis fibroblasts.There were full of collagen fibrils in intercellular matrix.Conclusions The collagen fibril is decreased and fibroblast cells are degenerated in lamina and fascia of conjunctivochalasis.