van Setten G-B
St Eriks Eye Hospital, Karolinska Institutet, Polhemsgatan 50, 11282 Stockholm, Sweden.
J Fr Ophtalmol. 2019 Mar;42(3):221-225. doi: 10.1016/j.jfo.2018.11.001. Epub 2019 Mar 7.
Tear fluid osmolarity has been increasingly accepted as an accessible parameter in the diagnosis of ocular surface and dry eye disease. After having been proposed as the gold standard, recent results have put this into question. However, the most recent guidelines for dry eye disease identify specific values of osmolarity as thresholds to help to differentiate between various stages of severity of ocular surface disease. The limits of this approach were investigated to propose a new concept, that of osmokinetics.
Available data on tear fluid osmolarity in normal and diseased eyes were compared. The possibility of normo-osmolar dry eye was investigated and repeated measurements of osmolarity performed.
The currently applied static model of a threshold value of osmolarity for diagnosing dry eye disease is apparently insufficient. Not only does it not take into account normo-osmolar dry eye, but it also applies too much significance to a single parameter. Instead, it was found that there is a daily variation in osmolarity (DVO), which appears to be higher in eyes with tear film deficiencies than in healthy eyes.
Tear film osmolarity does vary considerably throughout the day. Its value should be considered in a kinetic model taking into account the dynamics of osmolarity changes moreso than the current static model. The terms of osmotic stress and diurnal variation of osmolarity were found to offer a more physiological understanding of osmolarity.
A more dynamic model for osmolarity is presented in which not the value itself but the daily variation of osmolarity is identified. It is suggested that the amplitude of change in osmolarity over the course of a day or even shorter time periods could play a decisive role as a stress factor for the surface cells. The varying osmolar stress could be one of the key mechanisms leading to the cell death, inflammation, apoptosis, and goblet cell disappearance as observed in dry eye disease. Perhaps it is the mean osmolarity level at which these changes occur together with the magnitude of DVO which could identify the level of severity of dry eye disease.
泪液渗透压已越来越被视为眼表疾病和干眼病诊断中一个易于获取的参数。在被提议作为金标准之后，最近的结果对此提出了质疑。然而，最新的干眼病指南将特定的渗透压值确定为阈值，以帮助区分眼表疾病不同严重程度的阶段。对这种方法的局限性进行了研究，以提出一个新的概念，即渗透动力学。
比较了正常眼和患病眼中泪液渗透压的现有数据。研究了等渗性干眼病的可能性，并进行了渗透压的重复测量。
目前应用的用于诊断干眼病的渗透压阈值静态模型显然是不够的。它不仅没有考虑到等渗性干眼病，而且对单个参数赋予了过高的重要性。相反，发现渗透压存在每日变化（DVO），在泪膜缺陷的眼中，这种变化似乎比健康眼中更高。
泪膜渗透压在一天中确实有很大变化。在考虑渗透压变化动态的动力学模型中，应更多地考虑其值，而不是当前的静态模型。发现渗透压应激和渗透压的昼夜变化等术语能提供对渗透压更符合生理的理解。
提出了一个更具动态性的渗透压模型，其中确定的不是渗透压值本身，而是其每日变化。建议一天或更短时间段内渗透压变化的幅度可能作为表面细胞的应激因素发挥决定性作用。变化的渗透压应激可能是导致干眼病中观察到的细胞死亡、炎症、凋亡和杯状细胞消失的关键机制之一。也许是这些变化发生时的平均渗透压水平以及DVO的幅度可以确定干眼病的严重程度。
