Dept. of Bioengineering, Imperial College London, London, SW7 2AZ, UK.
Dept. of Bioengineering, Imperial College London, London, SW7 2AZ, UK.
Exp Eye Res. 2022 Jul;220:109103. doi: 10.1016/j.exer.2022.109103. Epub 2022 May 5.
The key risk factor for glaucoma is elevation of intraocular pressure (IOP) and alleviating it is the only effective therapeutic approach to inhibit further vision loss. IOP is regulated by the flow of aqueous humour across resistive tissues, and a reduction in outflow facility, is responsible for the IOP elevation in glaucoma. Measurement of outflow facility is therefore important when investigating the pathophysiology of glaucoma and testing candidate treatments for lowering IOP. Due to similar anatomy and response to pharmacological treatments, mouse eyes are a common model of human aqueous humour dynamics. The ex vivo preparation, in which an enucleated mouse eye is mounted in a temperature controlled bath and cannulated, has been well characterised and is widely used. The postmortem in situ model, in which the eyes are perfused within the cadaver, has received relatively little attention. In this study, we investigate the postmortem in situ model using the iPerfusion system, with a particular focus on i) the presence or absence of pressure-independent flow, ii) the effect of evaporation on measured flow rates and iii) the magnitude and pressure dependence of outflow facility and how these properties are affected by postmortem changes. Measurements immediately after cannulation and following multi-pressure facility measurement demonstrated negligible pressure-independent flow in postmortem eyes, in contrast to assumptions made in previous studies. Using a humidity chamber, we investigated whether the humidity of the surrounding air would influence measured flow rates. We found that at room levels of humidity, evaporation of saline droplets on the eye resulted in artefactual flow rates with a magnitude comparable to outflow, which were eliminated by a high relative humidity (>85%) environment. Average postmortem outflow facility was ∼4 nl/min/mmHg, similar to values observed ex vivo, irrespective of whether a postmortem delay was introduced prior to cannulation. The intra-animal variability of measured outflow facility values was also reduced relative to previous ex vivo data. The pressure-dependence of outflow facility was reduced in the postmortem relative to ex vivo model, and practically eliminated when eyes were cannulated >40 min after euthanisation. Overall, our results indicate that the moderately increased technical complexity associated with postmortem perfusion provides reduced variability and reduced pressure-dependence in outflow facility, when experimental conditions are properly controlled.
青光眼的主要风险因素是眼内压（IOP）升高，缓解眼压升高是抑制视力进一步下降的唯一有效治疗方法。IOP 由房水通过阻力组织的流动来调节，流出道阻力的降低是青光眼眼压升高的原因。因此，在研究青光眼的病理生理学和测试降低 IOP 的候选治疗方法时，测量流出道阻力是很重要的。由于眼睛解剖结构相似，对药物治疗的反应也相似，因此小鼠眼睛是研究人类房水动力学的常见模型。在体外制备中，将摘除的小鼠眼球安装在温度控制的浴槽中并进行插管，这种方法已经得到了很好的描述，并被广泛应用。而死后原位模型，即眼球在尸体中进行灌流，相对较少受到关注。在这项研究中，我们使用 iPerfusion 系统研究了死后原位模型，特别关注以下几个方面：i）是否存在压力独立的流量，ii）蒸发对测量流量的影响，iii）流出道阻力的幅度和压力依赖性，以及这些特性如何受到死后变化的影响。在插管后立即和多次压力设施测量后，与之前研究中的假设相反，我们发现死后眼球几乎不存在压力独立的流量。通过使用湿度室，我们研究了周围空气的湿度是否会影响测量的流量。我们发现，在室温下，盐水滴在眼球上的蒸发会导致与流出量相当的假象流量，而在高相对湿度（>85%）环境中则会消除这些假象流量。平均死后流出道阻力约为 4 nl/min/mmHg，与体外观察到的值相似，无论在插管前是否引入了死后延迟。与之前的体外数据相比，测量的流出道阻力值的个体间变异性也降低了。与体外模型相比，死后模型的流出道阻力的压力依赖性降低，并且在安乐死后超过 40 分钟进行插管时几乎消除。总的来说，我们的结果表明，与死后灌流相关的适度增加的技术复杂性提供了更低的变异性和更低的流出道阻力压力依赖性，只要实验条件得到适当控制。
